Geology of the Grand Canyon: Chapter V. The Toroweap And Uinkaret.

Updated February 28, 2017 | Infoplease Staff


The present chapter will contain an account of a journey from the village Kanab to the Toroweap Valley, and a description of the middle portion of the Grand Caon; also of the Uinkaret Plateau. Kanab is the usual rallying place and base of operations of the survey in these parts, being located on the only living stream between the Virgen and the Paria.

The first stage of the journey from Kanab to Pipe Spring is an easy one. It leads southwestward to a gap cut through the low Permian terrace, and out into the open beyond. The road, well traveled and casy, then turns westward and at length reaches the springs twenty miles from Kanab. Pipe Spring is situated at the foot of the southernmost promontory of the Vermilion Cliffs, and is famous throughout Southern Utah as a watering place. Its flow is copious and its water is the purest and best throughout that desolate region. Ten years ago the desert spaces outspreading to the southward were covered with abundant grasses, affording rich pasturage to horses and cattle. Today hardly a blade of grass is to be found within ten miles of the spring, unless upon the crags and mesas of the Vermilion Cliffs behind it. The horses and cattle have disappeared, and the bones of many of the latter are bleached upon the plains in front of it. The cause of the failure of pasturage is two fold. There is little doubt that during the last ten or twelve years the climate of the surrounding country has grown more arid. The occasional summer showers which kept the grasses alive seldom come now, and through the long summer and autumn droughts the grasses perished even to their roots before they had time to seed. All of them belong to varieties which reproduce from seed, and whose roots live but three or four years. Even if there had been no drought the feeding of cattle would have impoverished and perhaps wholly destroyed the grass by cropping it clean before the seeds were mature, as has been the case very generally throughout Utah and Nevada.

Northeastward the Vermilion Cliffs extend in endless perspective towards Kanab, and beyond to the Paria. Northwestward, with growing magnitude, they extend towards the Virgen, ever forming a mighty background to the picture. To the southward stretches the desert, blank, lifeless, and as expressionless as the sea. For five or six miles south of the Pipe Spring promontory there is a gentle descending slope, and thence onward the surface feebly ascends through a distance of thirty miles to the brink of the Grand Caon. Thus the range of vision is wide, for we overlook a gentle depression of great extent. Though the general impression conveyed is that of a smooth or slightly modulated country, yet we command a far greater expanse than would be possible among the prairies. To the southeastward the Kaibab looms up, seemingly at no great distance, and to the southwestward the flat roof of Mount Trumbull is more a blue cloud in the horizon. Towards this latter mountain we take a straight course. The first few miles lie across drifting sands bare of all vegetation. The air is like a furnace, but so long as the water holds out the heat is not enervating and brings no lassitude. Everything is calm and still, except here and there a hot whirling blast which sends up a tall, slender column of dust diffusing itself in the air. At a slow pace the sand-hills at length are passed and we enter upon a hard, firm soil, over which we move more rapidly. Just here, and for three or four miles in either direction, the Permian terrace has ben obliterated. It has ben beveled off by erosion and buried beneath the wash brought down from the foot of the Vermillion Cliffs to the northward. But seven miles from Pipe Spring, the Permian terrace springs up out of the earth, scarped by its characteristic cliff. Stretching northwestward it increases in altitude, becoming at last 800 to 1,000 feet high. At its summit is seen the Shinarump conglomerate, of a pale brown color, and beneath are the gorgeous hues of the shales. Nothing can surpass the dense, rich, and almost cloying splendor of the red-brown seen in these shales. They suggest the color of old mahogany, but are much more luminous and quite uniform. Under them are belts of chocolate, slate, lavender, pale Indian red, and white. Very wonderful, too, is the evenness of the bedding, which is brought out in great clearness and sharpness by the etching of minute layers of clays holding selenite. Between the shales and overlying conglomerate careful scrutiny enables us to detect an unconformity by erosion without any unconformity of dip. As stated in a preceding chapter, Mr. Wolcott fixed provisionally the separating horizon between the Permian and Trias at this unconformable contact.

Along the route the vegetation is scanty indeed. Several forms of cactus are seen looking very diseased and mangy, and remnants of low desert shrubs browsed to death by cattle. Yet strangely enough there is one plant and one alone that seems to flourish. It is the common sunflower (Helianthus lenticularis) , found anywhere from Maine to Arizona, and seeming indifferent to the vicissitudes of climate.

About 18 miles from Pipe Spring the trail leads gently down into a broad shallow valley known as the Wild Band Pockets. The drainage from the fronts of the Permian cliffs now far to the northward here collects into a gulch, which gradually deepens and becomes a tributary of Kanab Caon. In every stream-bed may be found many depressions which would hold water even though the sources of supply were cut off. This is as true of wet-weather channels as of perennial streams. After the infrequent showers, and after the surface waters have ceased to run, the bed of the stream will still retain pools of water, provided the bottom of it is of a consistency which will prevent it from filtering away. To these pools the people of the west have given the name of ?water-pockets.? They are very common in the stream-beds which bear away the wash from the Permian and lower Triassic shales. These shales yield a very fine impervious clay, which forms an excellent ?puddling? for water holes and basins. The Wild Band Pockets have received their name from the fact that they are the resort of bands of wild horses that roam over these deserts, far from human haunts, ranging from spring to spring, which they visit by stealth only at night, and never so long as they can find chance water in these and other pockets. Beyond the Wild Band Valley there is a slight ascent to a rocky platform, consisting of the summit beds of the Carboniferous. In the course of 20 miles we have crossed the entire Permian series, which now lies to the north of us. A few stunted cedars, most of which are dead or dying of drought, are scattered over this platform and give us until nightfall some slight shelter from the sun. It is as good a camping place as we are likely to find, and if we are fortunate enough to reach it after a copious shower, the hollows and basins in the flat rocks may contain a scanty supply of clear rain-water. It is a good locality, also, from which we may overlook the outspreading desert, which is not without charms, however repulsive in most respects.

To the northward rises the low escarpment of the Permian, forming a color picture which is somewhat indistinct through distance, but weird because of its strange colors and still stranger forms. Beyond and in the far distance rise the towering fronts of the Vermilion Cliffs, ablaze with red light from the sinking sun. To the eastward they stretch into illimitable distance, growing paler but more refined in color until the last visible promontory seems to merge its purple into the azure of the evening sky. Across the whole eastern quarter of the horizon stretches the long level summit of the Kaibab as straight and unbroken as the rim of the ocean. To the southwestward rises the basaltic plateau of Mount Trumbull, now presenting itself with somewhat imposing proportions. Around it a great multitude of basaltic cinder cones toss up their ominous black waves almost as high as Trumbull itself. Their tumultuous profiles and gloomy shades form a strong contrast with the rectilinear cutlines and vivid colors of the region roundabout.

At dawn we move onward, reaching soon the summit of a hill which descends two or three hundred feet to a broad flat depression called the Wonsits Plain. It is a smooth and very barren expanse, dotted with a few moldering buttes of Upper Carboniferous rocks, now wasted to their foundations. The plain is about seven miles in width, and on the further side rises a low mesa of great extent capped with basalt. It is the Uinkaret. Beyond the nearer throng of basaltic cones Mount Trumbull rises with a striking aspect dominating strongly the entire western landscape. The smaller cones are now seen to be very numerous, and all of them are apparently perfect in form, as if time had wrought no great ravage among them. The lapilli and peperino with which they are covered, has become dull red by the oxidation of the iron, and this peculiar color is easily recognized though the cones are still far away. Just before reaching the basaltic mesa we must make our choice between two routes to the Toroweap, one direct, the other very circuitous. No spring is to be found until we reach the further side of Mount Trumbull, but we know of a large water-pocket on this side, which has never been known to dry up. The spring water is sure to be good, but the water in the pocket will depend for its quality upon the length of time which has passed since the last heavy rain. Let us here choose the shorter one, and go to the water-pocket.

Ascending the mesa which rises abruptly about 200 feet above the Wonsits Plain, we find ourselves at once upon the basalt. The ground is paved with cinders and fragments half buried in soil, the dbris of decaying lava sheets. These sheets are rarely of any great thickness, seldom exceeding 30 or 40 feet, and often much less, and none of the individual eruptions of lava seem to have covered any very great expanse. Probably the area covered by the largest would be less than a square mile. They show no perceptible differences in composition or texture, and all are basalts of the most typical variety-very black and ferruginous in the unweathered specimens and speckled with abundant olivine. At the time of eruption they appear to have been in a state of perfect liquidity, spreading out very thin and flowing rapidly and with ease. In none of them has erosion wrought much havoc, though here and there some local destruction has been affected, most conspicuously upon the edges of the principal mesa where the sheets have been undermined and their fragments scattered upon the plain below. The cones, which stand thick around us, are still in good preservation. They are of ordinary composition-mere piles of cinders thrown out of central vents and dropping around it. The fume and froth of the lava surfaces, the spongy inflated blocks, the lapilli and peperino, are not greatly changed, though all of them here show the oxidation of the iron. We wonder what their age may be; what time has elapsed since they vomited fire and steam. But there is no clew-no natural record by which such events can be calendared. Historically they have doubtless stood in perfect repose for very many centuries. Not a trace of activity of any kind is visible, and they are as perfectly quiescent as the dead volcanoes of the Auvergne or of Scotland. Geologically, they are extremely recent; yet even here where historic antiquity merges into geologic recency the one gives us no measure of the other.

Following a course which winds among the silent cones and over rough, flat surfaces of lava beds half buried in drifting sands, we at length reach the border of a slight depression, into which we descend. It is hardly noteworthy as a valley just here, and might be confounded with any one of the innumerable shallow-water courses which occur round about; only when we look beyond we see it growing broader and much deeper. It is the head of the Toroweap. Upon its smooth bottom is a soft clayey soil, in which desert shrubs and stunted sage-brush grow in some abundance. Here and there a cedar, dwarfed indeed, but yet alive, displays a welcome green, and upon the valley slopes are a few sprays of grass. The valley bottom descends at a noticeable rate to the southward, and as we put the miles behind us we find the banks on either side rising in height, becoming steeper, and at last displaying rocky ledges. In the course of six or seven miles the left side has become a wall 700 feet high, while the others side, somewhat lower, is much broken and craggy. Huge piles of basalt lie upon the mesa beyond, sheet upon sheet, culminating in a cluster of large cones. At length the course of the valley slightly deflects to the left, and as we clear a shoulder of the eastern wall, which has hitherto masked it continuation, a grand vista breaks upon the sight. The valley stretches away to the southward, ever expanding in width; the walls on either side increase in altitude, and assume profiles of wonderful grace and nobility. Far in the distance they betoken a majesty and grandeur quite unlike anything hitherto seen. With vast proportions are combined simplicity, symmetry, and grace, and an architectural effect as precise and definite as any to be found in the terraces. And yet these walls differ in style from the Trias and Jura as much as the Trias and Jura differ from each other. In the background the vista terminates at a might palisade, stretching directly across the axis of vision. Though more than 20 miles, distant it reveals to us suggestions of grandeur which awaken feelings of awe. We know instinctively that it is a portion of the wall of the Grand Caon.

The western side of the valley is here broken down into a long slope descending from the cones clustered around the base of Mount Trumbull, and covered with broad flows of basalt. Turning out of the valley we ascend the lava bed, which has a very moderate slope, and about a mile from the valley we find the Witches' Water Pocket. In every desert the watering places are memorable, and this one is no exception. It is a weird spot. Around it are the desolate Phlegran fields, where jagged masses of black lava still protrude through rusty, decaying cinders. Patches of soil, thin and coarse, sustain groves of cedar and pion. Beyond and above are groups of cones, looking as if they might at any day break forth in renewed eruption, and over all rises the tabular mass of Mount Trumbull. Upon its summit are seen the yellow pines (P. ponderosa), betokening a cooler and a moister clime. The pool itself might well be deemed the abode of witches. A channel half-a-dozen yards deep and twice as wide, has been scoured in the basalt by spasmodic streams, which run during the vernal rains. Such a stream cascading into it has worn out of the solid lava a pool twenty feet long, nearly as wide, and five or six feet deep. Every flood [Fig. 7.-The Witches' Water Pocket.] fills it with water, which is good enough when recent, but horrible when old. Here, then, we camp for the night.

Filling the keg at daylight, we descend again into the Toroweap and move southward. Out attention is strongly attracted by the wall upon the eastern side. Steadily it increases its masses and proportions. Soon it becomes evident that its profile is remarkably constant. We did not notice this at first, for we saw in the upper valley only the summit of the palisade; but as the valley cuts deeper in the earth the plan and system begin to unfold. At the summit is a vertical ledge, next beneath a long Mansard slope, then a broad plinth, and last, and greater than all, a long, sweeping curve, descending gracefully to the plain below. Just opposite to us the pediments seem half buried, or rather half risen out of the valley alluvium. But beyond they rise higher and higher until in the far distance the profile is complete. In this escarpment are excavated alcoves with openings a mile wide. As soon as we reach the first one new features appear. The upper ledge suddenly breaks out into a wealth of pinnacles and statues standing in thick ranks. They must be from 100 to 250 feet high, but now the height of the wall is more than a thousand feet, and they do not seem colossal. Indeed, they look like a mere band of intricate fretwork-a line of balustrade on the summit of a noble facade. Between the alcoves the projecting pediments present gable-ends towards the valley plain. Yet whithersoever the curtain wall extends the same profile greets the eyes. The architect has adhered to his design as consistently and persistently as the builders of the Thebaid or of the Acropolis. As we pass alcove after alcove, and pediment after pediment, they grow loftier, wider and deeper, and their decoration becomes more ornate. At length we pass one which is vast indeed. It is recessed back from the main front threefourths of a mile, and shows three sides of an oblong room with walls 1,800 feet in height. The fourth side is obliterated and the space opens into the broad valley. Wonderfully rich and profuse are the pinnacles and statues along the upper friezes. The fancy is kindled as the eye wanders through the inclosure.

We looked across the valley, which is here three miles in width, and behold the other wall, which presents an aspect wholly different, but quite as interesting. The western wall the Toroweap is here lower than the eastern, but still is more than a thousand feet high. The geologist soon surmises that along the valley bottom runs a fault which drops the country on the west several hundred feet, and the conjecture soon becomes certainly. Above and beyond the western escarpment is the platform of the Uinkaret Plateau. Upon its summit is a throng of large basaltic cones in perfect preservation. Streams of lava larger than any hitherto seen have poured from their vents, flooding many a square mile of mesa land, and in the wide alcoves they have reached the brink of the wall and cascaded over it. Still pouring down the long taluses they have reached the valley bottom below and spread out in wide fields, disappearing underneath the clayey alluvium, which has buried much of their lower portions. The appearance of these old lava cascades, a mile or more wide, a thousand feet high, and black as Erebus, is striking in the extreme. There are five of these basaltic cataracts, each consisting of many individual coules. Between them the bold pediments of brightly-colored Carboniferous strata jut out into th valley.

At length we approach the lower end of the Toroweap. The scenery here becomes colossal. Its magnitude is by no means its most impressive feature, but precision of the forms. The dominant idea ever before the mind is the architecture displayed in the profiles. It is hard to realize that this is the work of the blind forces of nature. We feel like mere insects crawling along the street of city flanked with immense temples, or as Lemuel Gulliver might have felt in revisiting the capital of Brobdingnag, and finding it deserted. At the foot of the valley the western wall is nearly 1,500 feet high, the eastern about 2,000, and the interval separating them is about three miles. Suddenly they turn at right angles to right and left, and become the upper wall of the Grand Caon of the Colorado. The Torowealp now opens into the main passageway of the great chasm. The view, however, is much obstructed. [U. S. GEOLOGICAL SURVEY. PANORAMA FROM MOUNT TRUMBULL Upper view looking East, with the Grand Caon in the distance. Lower view looking down the Toroweap. ANNUAL REPORT 1881. PL. XXIII.] [U. S. GEOLOGICAL SURVEY. PANORAMA FROM MOUNT TRUMBULL Upper view looking East, with the Grand Caon in the distance. Lower view looking down the Toroweap. ANNUAL REPORT 1881. PL. XXIII.] [Fig. 8-The brink of the Inner Gorge at the foot of the Toroweap, looking east] At the foot of the eastern gable is a medley of rocky ledges of red sandstone, while around the base of the western gable are large masses of basalt reaching more than half-way across the valley. In front rises a crater, which is about 600 feet high, seemingly a mere knoll in the midst of this colossal scenery. Beyond it, and five miles distant, rises the palisade which forms the southern upper wall of the chasm, stretching athwart the line of vision interminably in either direction. Its altitude is apparently the same as that of the palisade above us, and its profile is also identical. Climbing among the rocky ledges which lie at the base of the escarpment, we at length obtain a stand-point which enables us to gain a preliminary view of the mighty avenue. To the eastward it stretches in vanishing perspective forty miles or more. Between symmetric walls 2,000 feet high and five miles apart is a plain, which in comparison with its limiting cliffs might be regarded as smooth, but which in reality is diversified by rocky hummocks and basins, and by hillocks where patches of soil give life to scattered cedars and pions. Of the inner chasm nothing as yet is to be seen. Moving outward into this platform we find its surface to be mostly bare rock, with broad shallow basins etched in them, which hold water after the showers. There are thousands of these pools, and when the showers have passed they gleam and glitter in the sun like innumerable mirrors. As we move outward towards the center of the grand avenue the immensity and beautiful proportions of the walls develop. The vista towards the east lengthens out and vanishes against the blue ramp of the Kaibab, which lies as a cloud upon the horizon. To the west the view is less symmetric and regular, and the eye wanders vaguely among cliffs and buttes of stupendous magnitude, displaying everywhere the profile with which we have become of late familiar. Much of the distance towards the west is obstructed by the crater, but the portions in view bewilder us by the great number of objects presented, and oppress us by their magnitudes. At a distance of about two miles from the base of the northern wall we come suddenly upon the inner chasm. We are not conscious of its proximity until we are within a few yards of it. In less than a minute after we have recognized the crest of the farther wall of this abyss we crane over its terrible brink and gaze upon the waters of the river full 3,000 feet below.

The scene before us is a type of the Grand Caon throughout those portions which extend through the Kanab, Uinkaret, and Sheavwits Plateaus. The plan and section here presented are quite simple. They consist of a broad upper chasm from five to six miles in width with walls varying in altitude but little from 2,000 feet. Between these escarpments is a rocky plain, rough indeed, but in the overpowering presence of such walls seeming relatively smooth and uniform. In this floor is cut the inner chasm 3,000 feet deep and from 3,500 to 4,000 feet wide from crest to crest. The true profile will be best understood by consulting the diagram, Fig. 10, which is drawn to scale. The strata in which the chasm is excavated are all of Carboniferous age excepting three or four hundred feet at the bottom of the gorge. The strata beneath the Carboniferous are at present believed to be Lower Silurian, and their contact with the Carboniferous is unconformable, both by dip and by erosion. In the upper part of the palisades which form the wall of the upper chasm we find at the summit two series of limestones. The upper contains an abundance of siliceous matter, one portion of which is intimately disseminated through the mass while another portion is aggregated into myriads of cherty nodules varying from two to ten inches in diameter. The lower one is a purer limestone with few nodules. The cherty members form a nearly vertical band at the summit of the wall; the purer members form a Mansard slope beneath, covered with talus. The total thickness of the limestones is about 700 to 750 feet. Beneath them come



[Fig. 9-The brink of the Inner Gorge at the foot of the Toroweap, looking east]

sandstones a little more than 250 feet thick, which form everywhere a vertical plinth or frieze. They are very adamantine in texture, and one of the members, about 160 feet thick, is in every exposure seen to be uniformly cross-bedded. Under the cross-bedded sandstone is a mass of thinly bedded and almost shaly sandstones, having an aggregate thickness very closely approximating to 1,000 feet. They are of an intensely brilliant red color, but are, in greatest part, covered with a heavy talus of imperishable cherty nodules, fragments of the cross-bedded sandstones, and spalls of limestones shot down from above. The color of these is pale grey, with occasionally a yellowish or creamy tinge. The brilliant red sandstones form the long curved slope which descends from the plinth of cross-bedded sandstone to the plain below.

[Fig. 10-Section of the grand Caon at the foot of the Toroweap Valley; 2, Lower Aubrey; 3 Red Wall;4, Base of the Carboniferous; 5, Lower Silurian and Archan unconformable. Scale one mile to the inch.]

The walls of the inner gorge have at the summit about 325 feet of hard sandstone of a brown-red color. Beneath the sandstone are about 1,800 feet of impure limestone in layers of the most massive description. Very few such ponderous beds of limestone are found in any part of the world. The color is deep red with a purplish tone, but the brilliancy of the coloring is notably weakened by weathering. Still lower are red-brown sandstones again having a dark and strong shade and lying in very massive beds. The strata forming the walls of the outer chasm from the summit to the plain below are designated the Aubrey group, and this is again subdivided at the base of the cross-bedded plinth into Upper and Lower Aubrey groups. The two subdivisions are believed to be the equivalents, in age, of the Coal Measures of Pennsylvania and England. The strata disclosed in the inner gorge correspond in age to the Lower Carboniferous of those countries, and are here termed the Red Wall group. Some uncertainty exists regarding the beds which lie at the base of the conformable series deep down in the chasm, but they are regarded at present as being just what they seem and just what they would naturally be inferred to be-a part of the Carboniferous system. Of the strata at the bottom of the caon, we shall have more to say hereafter. They are regarded at present as being of Lower Silurian or Primordial age.

The observer who, unfamiliar with plateau scenery, stands for the first time upon the brink of the inner gorge, is almost sure to view his surroundings with commingled feelings of disappointment and perplexity. The fame of the chasm of the Colorado is great; but so indefinite and meager have been the descriptions of it that the imagination is left to its own devices in framing a mental conception of it. And such subjective pictures are of course wide of the truth. When he first visits it the preconceived notion is at once dissipated and the mind is slow to receive a new one. The creations of his own fancy no doubt are clothed with a vague grandeur and beauty, but not with the grandeur and beauty of nature. When the reality is before him the impression bears some analogy to that produce upon the visitor who for the first time enters St. Peter's Church at Rome. He expected to be profoundly awe, struck by the unexampled dimensions, and to feel exalted by the beauty of its proportions and decoration. He forgets that the human mind itself is of small capacity and receives its impressions slowly, by labored processes of comparison. So, too, at the brink of the chasm, there comes at first a feeling of disappointment; it does not seem so grand as we expected. At length we strive to make comparisons. The river is clearly defined below, but it looks about large enough to turn a village grist-mill; yet we know it is a stream three or four hundred feet wide Its surface looks as motionless as a lake seen from a distant mountain-top. We know it is a rushing torrent. The ear us strained to hear the roar of its waters and catches it faintly at intervals as the eddying breezes waft it upwards; but the sound seems exhausted by the distance. We perceive dimly a mottling of light and shadow upon the surface of the stream, and the flecks move with a barely perceptible cloud-like motion. They are the fields of white foam lashed up at the foot of some cataract and sailing swiftly onward.

Perhaps the first notion of the reality is gained when we look across the abyss to the opposite crest-line. It seems as if a strong, nervous arm could hurl a stone against the opposing wall-face; but in a moment we catch sight of vegetation growing upon the very brink. There are trees in scattered groves which we might at first have mistaken for sage or desert furze. Here at length we have a stadium or standard of comparison which serves for the mind much the same purpose as a man standing at the base of one of the sequoias of the Mariposa grove. And now the real magnitudes begin to unfold themselves, and as the attention is held firmly the mind grows restive under the increasing burden. Every time the eye ranges up or down its face it seems more distant and more vast. At length we recoil, overburdened with the perceptions already attained and yet half vexed at the inadequacy of our faculties to comprehend more.

The magnitude of the chasm, however, is by no means the most impressive element of its character; nor is the inner gorge the most impressive of its constituent parts. The thoughtful mind is far more deeply moved by the splendor and grace of Nature's architecture. Forms so new to the culture of civilized races and so strongly contrasted with those which have been the ideals of thirty generations of white men cannot indeed be appreciated after the study of a single hour or day. The first conception of them may not be a pleasing one. They may seem merely abnormal, curious, and even grotesque. But he who fancies that Nature has exhausted her wealth of beauty in other lands strangely underestimates her versatility and power. In this far-off desert are forms which surprise us by their unaccustomed character. We find at first no place for them in the range of our conventional notions. But as they become familiar we find them appealing to the sthetic sense as powerfully as any scenery that ever invited the pencil of Claude or of Turner.

The inner gorge, as we sit upon its brink, is indeed a mighty spectacle; but as we withdraw a little, it fades out of view, and, strangely enough, the sublimity of the scene is not very greatly impaired. It is, after all, a mere detail, and the outer chasm is the all engrossing feature. On either side its palisades stretch away to the horizon. Their fronts wander in and out, here throwing out a gable, there receding into a chamber or gaping widely to admit the entrance of a lateral chasm. The profile is ever the same. It has nothing in common with the formless, chaotic crags, which are only big and rough, but is definite, graceful, architectural, and systematic. The width of the space inclosed between the upper walls is one of the most essential elements of the grandeur. It varies from five to six miles. If it were narrower the effect would be impaired; nor could it be much wider without diluting and weakening the general effect. This proportion seems quite just. It is common notion that the distinctive and overruling feature of the great chasm is its narrowness relatively to its depth. No greater mistake could be made. Our highest conceptions of grandeur are most fully realized when we can see the greatest mass. We must have amplitude in all of the three dimensions, distance, breadth, and depth, and that spectacle is in point of magnitude the grandest which has the three dimension so proportioned and combined as to make the most of them. Another common and mistaken idea is that the chasm is pervaded by a deep, solemn gloom. The truth is almost the reverse. In the depths of the inner gorge there is a suggestion of gloom, but even in the narrower portions there is seldom less than sixty degrees of sky from crest to crest, and a hundred and sixty along the track of the river. In the outer chasm the scene is unusually bright. The upper half of the palisades have a pale, ashy, or pearl-gray color, which is very lustrous, and this sometimes gives place to a creamy or Naples yellow tint in the frieze of cross-bedded sandstone. The Lower Aubrey sandstones are bright red, but they are in great part masked by the talus shot down from the pale gray limestones above, and peep out in lustrous spots where the curtain of the talus is drawn aside. There is nothing gloomy about such colors. Under a burning sun that i s rarely clouded they have a brilliancy seldom seen in any rocks, and only surpassed by the sugary whiteness of the Jurassic sandstone or the brilliant red of the Vermilion Cliffs.

Directly in the southward prolongation of the axis of the Toroweap Valley there stands a basaltic cinder-cone immediately upon the brink of the inner gorge. Its altitude above the surrounding plain is 580 feet. The summit is readily gained, and it is an admirable stand-point from which the entire panorama may be viewed. We named it Vulcan's Throne. To the eastward about forty miles of the main chasm are well in view. The altitude of the cone, though small in comparison with surrounding objects, is sufficient to bring into view about twelve miles of the opening of the inner gorge, while in the foreground its depths are seen. To the westward the scenery is much more broken and diversified. The chasm is seen through the entire stretch in the Uinkaret Plateau and reaching a few miles into the Sheavwits. But about twenty miles westward it makes a southward turn and disappears. From the north the Toroweap Valley descends from near Mount Trumbull. It is cut down only to the level of the plain above the inner gorge. There is reason to believe that at some prior epoch it was cut a few hundred feet deeper than its present floor, and was subsequently built up by many floods of basalt coming from the cones on the Uinkaret and by considerable quantities of alluvium washed from its cliffs and overlooking mesas. On the south side of the Grand Canon is a valley quite the counterpart of the Toroweap. It enters the main chasm directly opposite to the Toroweap, so that the two form the arms of a transept, the main chasm being regarded as the nave. Vulcan's Throne is situated almost exactly at the intersection of the axes of nave and transept.

It would be difficult to find anywhere else in the world a spot yielding so much subject-matter for the contemplation of the geologist; certainly there is none situated in the midst of such dramatic and inspiring surroundings. The chasm itself, with its marvelous story of erosion, and the two lateral valleys adding their quotas of information are grand subjects indeed; but other themes are disclosed which are scarcely less surprising and suggestive. The cone stands immediately upon the line of a large fault. And never was a fault and its consequences more clearly displayed. The Toroweap fault is one of six which at wide intervals traverse the Grand Caon district from north to south with a rude approximation to parallelism. It is the smallest of the six. Twenty miles north of the chasm no trace of it is visible. Its beginning there is small, but as it approaches the chasm it increases in the amount of displacement; and at the crossing of the river the shear or ?throw? is between 600 and 700 feet. In the wall-face of the inner gorge it is disclosed as clearly as a draughtsman could delineate it on paper. The masses of horizontal limestones and sandstones, displaying their fretted edges and lines of bedding, advance from the eastward in the face of the wall until they reach the vertical fault plane. Then they ?break joints? and drop at once six or seven hundred feet, and continue westward as before, but at a lower level. The whole topography goes with it. Looking beyond to the upper wall of the outer chasm the ?jog? where the break occurs is plainly seen. The whole platform of the country is dropped to the westward. The plain between the upper palisades descends by a single step from east to west across the fault by an amount equal to the displacement, and the inner gorge and the whole chasm becomes by so much reduced in depth.

Excepting the dislocation itself, the faulting does not appear to have been accompanied by any injury to the strata. Not a trace of shattering, crumbling, or mashing of the beds is discernible. All looks as clean and sharp as if it had been cut with a thin saw and the smooth faces pressed neatly together. But the only attainable view of it is from the distance of a mile. Yet miles here are less than furlongs in other countries, and all details as well as broader features are upon the Brobdingnagian scale. What a nearer view might disclose is of course impossible to conjecture. The plane of the fault is about vertical, though there seems to be a slight inclination to the east, which may be apparent only and a result of perspective.

After a careful study of the surroundings of the fault, it becomes apparent that it is of recent occurrence in comparison with other events which have been in progress here. The tenor of all evidence bearing upon the subject goes to show that these faults were not suddenly produced by violent convulsions, but gradually developed through long stretches of time, and inch by inch or foot by foot. The Toroweap fault gives no evidence of being exceptional in this respect. Its recency is disclosed by many facts. It is seen that the amount of erosion in the face of the transverse ?cliff of displacement? produced by the faulting is very small. This cliff has not receded from the fault plane to any considerable extent. Yet the giant palisades which wall the outer chasm have receded from the median line of the caon more than two miles since the corrasion of the river laid bare the edges of their strata. It seems very plain that the outer chasm had been formed and attained very nearly its present condition before th fault started. But there is still more conclusive evidence of recency. At the foot of the southern palisade and at the jaws of the lateral valley are several basaltic craters. They look like mere bee-hives under the eaves of such an escarpment, though in truth they are four or five hundred feet high. From their vents streams of basalt are seen flowing down into the lateral valley across the fault plane, and clear to the brink of the inner abyss. The fault shears the lava floods as neatly as it does the Red Wall limestone.[1]* Many other facts might be cited to the same purport, but this one is so conclusive that nothing further is necessary. We shall find similar evidences of recency when we come to the study of the great Hurricane fault.

Another subject which will awaken the enthusiasm of the geologist who visits this unique spot is the volcanic phonomena. Turning to the northwestward he beholds the heights of the Uinkaret. Upon its broad expanse stand many basaltic craters in perfect preservation. We know of about a hundred and fifty distinct cones in this plateau, included in the space which lies between the Grand Caon and a limit forty miles north of it. But it is in the vicinity of the chasm that they cluster most thickly together and present the largest proportions. This part of the Uinkaret is thickly covered with basalt, above which rises the tumultuous [U. S. GEOLOGICAL SURVEY LOOKING UP THE TOROWEAP VALLEY. LAVA CASCADES. ANNUAL REPORT 1881. PL. XXV.] [U. S. GEOLOGICAL SURVEY LOOKING UP THE TOROWEAP VALLEY. LAVA CASCADES. ANNUAL REPORT 1881. PL. XXV.] throng of craters. Very many wide and deep floods of basalt have poured over the edge of the plateau into the lower Toroweap Valley and upon the great esplanade of the caon, 1,500 to 1,800 feet below, and, spreading out into wide fields, have reached the brink of the inner gorge. Pouring over its brink, the fiery cascades have shot down into the abyss and pursued their way many miles along the bed of the river. At one epoch they had built up the bed of the Colorado about 400 feet, but the river has scoured out its channel again and swept them all away, regaining its old level, and is now cutting the sandstones below. The spectacle of the lava floods descending from the Uinkaret, as seen from Vulcan's Throne, is most imposing. It tells the story so plainly that a child could read and understand it. Compared with many classic volcanic regions the volcanism of the Uinkaret is a small affair. In those classic regions the mind does not come into direct contact with the enormity of the facts by a single glance of the eye. But here, if kind Asmodeus were to lift the basaltic roof of the plateau, we should see no more than we do now. The boldness of the picture is much increased by the pediments of Carboniferous strata projecting from the body of the plateau, showing the brilliant colors of the strata and their sharply-defined architecture, with the dark masses of basalt wrapping around them. Hard by, and almost within hail, is a superb gable projecting between two broad floods of lava, and so beautifully proportioned and richly colored that we cannot help wishing to transport it by magic to some more habitable region.

The Toroweap Valley has a significance to the geologist which might not be at once apparent to the tourist. Even the geologist would be slow to discern if unless familiar with cognate facts displayed in the country at large bordering the Grand Caon. In the effort to interpret its meaning it becomes necessary to take a hasty view of one or two broad facts relating to the lateral drainage of the chasm. Upon the north side, in all the distance between the head of the Marble and the foot of the Grand Caons, there is but one side caon carrying drainage from distant regions. This single exception is Kanab Caon. In this respect the Colorado is much like the lower courses of the Nile; and the cause is plainly the same. The region is too arid to sustain any living streams or even to keep open the conduits which in former periods might have sustained them. Yet upon the assumption that at some former period the climate was much more humid all analogy compels us to believe that the Colorado once received many tributaries which are now extinct, and upon examination we find good evidence that this was really the case. The Toroweap Valley is the modified channel of an ancient river. On the west side of the Uinkaret is another. A third is seen upon the south side of the Colorado, directly opposite the Toroweap; and a few others may be easily designated. It appears that all these rivers dried up before the inner gorge was excavated. For if they had continued to carry water we may be sure that they would have cut their chasms as deep as the Grand Caon itself-just as the Little Colorado, Kanab Creek, and Cataract Creek have done. For we have only to look at the great multitude of lateral chasms of the upper courses of the Colorado and of its fork, the Grand and Green, to be deeply impressed with the fact that so long as a tributary river carries, we will not say a living stream, but even occasional floods, its channel will be scoured down to the same level as the trunk river itself. It is apparent, then, that the Toroweap dried up before the cutting of the inner gorge of the Grand Caon began, and hence we infer that the arid climate which caused it to dry up existed before the beginning of the inner gorge.

By the application of other homologous facts, and by the same method of reasoning, we infer that the outer chasm has also been excavated during the prevalence of an arid climate. The platform of country adjoining the caon is at present devoid of lateral chasms, yet traces are often found of ancient channels which became dry at about the time the excavation of the outer caon began, or very soon thereafter. They are cut to comparatively slight depths-from one hundred to three or four hundred feet. That they are not of recent origin is proved by the fact that they often have slopes away from the river, though it is clear that they formerly sloped towards it. In truth, the entire chasm betrays everywhere the continued action of an arid climate through the entire period of its formation. This arid period is limited, approximately, to Pliocene and Quaternary time. The general tenor of the facts is to the effect that the Miocene was a humid period and the Pliocene a dry one throughout the greater part of the West. This is one of the reasons which lead us to the very probable conclusion that the age of the Grand Caon is not older than the beginning of Pliocene time. We might also draw a similar inference from a consideration of the enormous erosion which took place here before the excavation of the chasm was begun. The denudation of the Mesozoic system was an incomparably greater work, and yet that denudation could not have begun until the last strata (the Lower Eocene) were deposited. If these inferences are well founded, we may assign the greater part of Eocene and the whole of Miocene time for the principal denudation of the Mesozoic, and the Pliocene and Quaternary for the excavation of the entire caon. The proportion thus suggested between the portions of the work done and the divisions of time required to accomplish them seems very fair and reasonable. But the strongest evidence of all it would be almost impossible to recite here in detail. In general terms, it may be characterized as that internal evidence which appears when a vast array of facts, at first disjointed and without obvious relation, are subsequently grouped aright into a coherent system. Each constituent fact is then seen to admit of one intelligible interpretation and no other; and each subsidiary proposition has an overwhelming justification and an evidence of verity far stronger than any which could be summoned if we endeavored to prove it independently.

Another question which the geologist asks here is, how happens it that the outer chasm is so broad while the inner one is so narrow? The outer chasm is five to six miles wide and 2,000 feet deep; the inner is about 3,500 feet wide and 3,000 feet deep. The disparity is great. We have seen enough to say at once that the widening of the outer chasm was effected by the recession of its cliffs. If the corrasion of the caon went steadily onward without a halt or respite this disparity demands some explanation. Although we should expect less recession in the cliffs of the inner gorge than in those of the outer, we should not expect it to be so much less if the only variable concerned was length of time. We might explain it by assuming the rocks of the inner gorge to be much more obdurate than those above. This is true in part, but still the difference in this respect is insufficient. A much more satisfactory explanation is found in the supposition that the broad esplanade of the caon between the upper palisades was an ancient base-level of erosion (page 101). We might imagine that when the Colorado had cut its channel down to that level, it had reached the limiting depth of corrasion for the time being. Then for a long period the palisades on either side wasted and receded from the river. At last another epoch of upheaval set in; the entire platform of the district was lifted several thousand feet; the power of the river to corrade was restored; and with comparative rapidity it sank the inner gorge. This becomes more than a mere guess when we take account of its relation to the general category of facts. Thus the great faults attest the fact that such an upheaval did occur; that it occurred, too, just at the time supposed; and that in amount it was quite equal and probably not more than equal to the amount required. Other evidences might also be produced, but they are too intricate to be discussed here.[2]*

We leave the Toroweap Valley and the Grand Caon, regretting that all its wonderful and instructive subjects should receive such brief notice. Retracing our steps up the Toroweap for a distance of about six miles, we at length select one of the great lava streams on the western side. Although quite steep, we may ascend it with the animals and packs without serious difficulty. At the end of an arduous climb upon the rugged slope, we find ourselves upon the platform of the Uinkaret. Around us are the old cinder-cones, most of which are of considerable dimensions. All of them have given vent to floods of basalt, which have spread out thinly over extensive surfaces, but as the number of superposed sheets is considerable in this part of the plateau, the aggregate thickness, though somewhat roughly inferred, must be three or four hundred feet, and occasionally much more. There is not much to add to this description. The lava is apparently all of one kind, but some of it much older than other portions. In truth, it soon becomes apparent that the period of volcanic activity was a long one. A few miles from the point where we attained the summit of the plateau and in a northwest direction from it, we come upon the termination of a lave stream which has the appearance of being extremely recent. It looks as fresh as the emanations from Vesuvius or tna which have outflowed within the last fifty years. Its surface is intensely black, and only here and there can we perceive that weathering has even impaired its freshness. Two miles away is seen the cone from which it emanated. The last eruptions from it have almost destroyed it, and melted down the greater part of its mass.

Skirting the edge of this lava-sheet, we find at the eastern base of Mount Logan a small spring, named the Oak Spring. It is a central point, from which the southern part of the plateau may be visited. There is another very small spring high up on the southwestern side of Mount Trumbull, and its waters have been brought down by a wooden pipe to the plain below, to supply the wants of a saw-mill. A third and much larger spring is found on the western side of the Uinkaret. These are only available sources of supply, and each may be used as occasion requires for the examination of different parts of the plateau.

It will be necessary here to advert, with the greatest brevity, to the facts which the Uinkaret presents. Its most conspicuous subject is its volcanism. Almost as striking a subject is the great Hurricane fault, which forms the western boundary of the plateau. It also presents many other features of interest, but only the briefest allusion to them can be made here.

The lavas of the Uinkaret are all basaltic, and are quite typical of their class. They appear to vary but little in their constitution, and, so far as the cursory examination hitherto made indicates, the only differences are such as are incident to varying conditions under which they solidified after eruption, or to subsequent weathering. But is also appears that the period of volcanic activity has covered a considerable duration of geological time. There are old lavas and young lavas; perhaps we may say there are middle-aged lavas. The older lavas are presented in the largest masses, the largest individual Coules. Another noteworthy feature is that the oldest lavas are now found upon the summits of the loftiest portions of the plateua, while the younger lavas are found chiefly on the lower levels. It is well worth studying to see how this comes about. The facts and explanation are best presented in the fine mass of Mount Trumbull.

This mountain is in reality a gigantic butte; that is to say, a mass of [U. S. GEOLOGICAL SURVEY RECENT LAVA A STREAM ON THE UINKARET. ANNUAL REPORT 1881. PL. XXVI.] sensibly horizontal strata left by the denudation of the same beds from the platform surrounding. It is roofed over with a ponderous lava-cap, 500 to 800 feet thick. Under this lava-cap are seen in numerous places the horizontal edges of the strata, though the flanks of the mountain are so thickly covered with the dbris formed by the disintegration of the basalts at the summit that these strata are for the most part buried. The beds beneath the lava are of Permian age, and it is evident that nearly the whole and possibly quite all of the Permian series remains in the mountain mass. That these basalts are very old is evident at a glance. The evidences of erosion are seen or every hand, and their aspect is strikingly different from that of the younger or middle aged basalts. On the summit of the mountain we find a cluster of old vents, from which a great part at least of these lavas were expelled. They are simply large craters torn down, dissolved and rotted away to their very roots by the ravage of time. It is evident, too, that the lave-cap itself is as a whole a mere remnant of a mass of superposed sheets which once extended much beyond the steep ledge which now limits them all around the mountain. The geologist draws his conclusion very quickly. These basalts in the lava-cap were extravasated at a time when the aspect of the surrounding country was very different from that which is now presented. At that time large bodies of Permian strata, since swept away extended continuously from the edges now exposed in the mountain flanks over spaces far way from it. We cannot indeed affirm that the great denudation had not already begun its havoc in the Permian, but we may be sure that it had not reached nearly its present stage. Mount Trumbull then is a remnant of a platform of lava-capped Permian beds, which was once of much greater extent. What was the extent of this platform at the time of the eruptions, we do not yet know, nor are we likely to know.

Around the base of the mountain on all sides the more recent craters are thickly clustered. The cones are for the most part in an admirable state of preservation; though here and there one may be found which has suffered considerable ravage. About two miles north of the base of Trumbull, especially, is an old cone, which has been laid open in such a manner as to disclose its interior structure very clearly. It is in all respects similar to the cones of the Mediterranean islands and countries. All of these craters were built at a much later period than the lave-cap of the mountain.

Mount Logan which lies near Trumbull to the southwestward, presents a similar state of affairs. It is a tabular mass capped with the more ancient basalts and with a great body of Permian beds beneath. South of Logan is another mass of ancient basalts, overlying Permian strata. Upon this southern table, however, are planted some well preserved craters which belong to the middle age of eruptions. Chief among these is Mount Emma, whose summit has been used as a primary topographical station. In general, these more ancient basalts appear to have been erupted at a time when the summit of the Permian constituted the principal part or certainly a great part of the platform of the country. Since their outflow, the great denudation has made progress, so that at present only these lava-capped and lofty masses remain. A considerable number of patches of the basal members of the Permian, however, are still preserved in the country roundabout, while the greater part of the Permian series has been removed. It is indeed quite possible that at the time of the eruption of the most ancient basalts, considerable ravage may have already been made in the Permian strata; but the probabilities are that the amount of such destruction was not very great.

It is not easy, perhaps it is impossible, to fix the relative age of these eruptions in geological terms. It is, however, certain that they date well back in Pliocene time, and may even have taken place in late Miocene time. I am inclined to refer them, doubtfully, indeed, yet not wholly at random, to an epoch in which the excavation of the Grand Caon had either just begun or had made only a little progress. This period, with somewhat more confidence, I assign to the early part of the Pliocene. The middle-aged eruptions, of course, were much later, and may come not far from the glacial epoch, but whether immediately before or immediately after, or during that period, I see no means of determining. The later eruptions are in all probability Quaternary, and it can hardly be doubted that the very fresh lava streams already spoken of had their eruption within the Christian era; nay, they may have broken forth since the conquest of Mexico by Cortez. Some light is thrown upon the question of age by a study of the great Hurricane fault.

The Uinkaret Plateau is bounded on the west at the brink of an escarpment differing radically from the cliffs of the terraces. So far as outward topographic features are concerned, the superficial observer would not note any marked peculiarity. But its origin is wholly different. The terrace cliffs are all cliffs of erosion, produced by the denudation of the country in front of them. The Hurricane Cliff which bounds the Uinkaret is a cliff of displacement. At its base is a gigantic fault, letting down the whole country to the westward as far as the eye can reach. The Hurricane fault has its southern end far south of the Colorado-we know not where at present-but we do know that it extends south of the river, with a great amount of displacement, for more than thirty miles; and at the farthest point thus far observed it has still great force, and shows no signs of vanishing or running out. At the point where it crosses the Colorado it has a shear of about 1,400 feet, and the displacement increases northward. Abreast of the southern portion of the Uinkaret it is no longer a single fault, but suddenly splits into four branches or steps, the ?throw? being distributed irregularly among the several steps. To see this we must descend into the Queantoweap Valley, lying on the west side of the Uinkaret, and, in some sense, the mate or homologue of the Toroweap on the eastern side. Reaching the bottom we [U. S. GEOLOGICAL SURVEY. LOOKING NORTHEAST FROM MOUNT EMMA. MOUNTS LOGAN AND TRUMBULL IN THE DISTANCE ANNUAL REPORT 1881. PL. XXVII.] [U. S. GEOLOGICAL SURVEY. LOOKING NORTHEAST FROM MOUNT EMMA. MOUNTS LOGAN AND TRUMBULL IN THE DISTANCE ANNUAL REPORT 1881. PL. XXVII.] descend the Queantoweap a few miles, and turning about we see the effects of the fault so plainly that a child could hardly mistake them. Right in the bottom of the valley is the lower branch with a displacement of about 1,300 feet. (Plate XXVIII). On the cliff to the right is a second smaller displacement of about 350 feet. Still farther to the right is a third of about 700 feet. Beyond the limits of the diagram is a fourth of about 500 feet. Twenty-five miles north of the Colorado the branches have disappeared and a single fault remains, with a shear of about 1,800 feet, and this amount continues nearly constant to the northward for a few miles. At length the fault rapidly increases. Seventy-five miles north of the river, and at the point where the Virgen River crosses it, the throws has become colossal. We stand upon the brink of the cliff with our feet upon the summit of the Carboniferous, and within musket range, 1,500 feet below, is the Jurassic white sandstone. Most of the Jurassic (800 feet), the whole of the Trias, which here has unusual thickness (2,800 or 2,900 feet), and the whole of the Permian and Permo-Carboniferous (1,200 or 1,300 feet), overlie the continuation of the strata on which we stand. The total throw is not far from 6,500 feet. Still northward extends the fault, and still it rapidly increases. At length it reaches a maximum displacement of more than 12,000 feet on the west side of the Markgunt. Continuing northward it gradually decreases, and finally disappears near the western flank of the Tushar Mountains. The entire length of this fault is more than 200 miles. It is throughout its whole extent a primary geological and topographical feature of the region it traverses.

With regard to the age of the fault we have some information. It is not probable that all its portions were sheared simultaneously, and it is quite certain that its development was very slow and gradual and progressed through a long stretch of geological time. Confining our attention to that portion extending along the western flank of the Uinkaret, we find that early the whole displacement took place after the eruption of the oldest basalts, for the fault dislocates the most ancient lava beds. Whether some small portion of it may or may not have existed before these eruptions we cannot positively say, but no evidence of such priority has been noted. On the other hand, all the younger lavas, and some, at least, of the middle-aged lava flowed across the fault and have not since been cut by it. But some of the middle-aged lavas appear to have suffered some dislocation. Hence we infer (1), That the age of this part of the Hurricane fault is not older than the beginning of the Pliocene. (2), That the displacement went on in harmony and conjunction with the volcanic activity. (3), That for a long period, historically speaking, it has been quiescent, and no movement has within the historic epoch taken place. (4), That the beginning of the Hurricane fault is older than the beginning of the Toroweap fault. These conclusions are of great importance in unraveling the history of the Grand Caon district, for they at once become links in a chain of reasoning which, though complex, is very systematic and self-consistent. The faults are evidences of vertical movements. The amount of shearing and the time of its occurrence give us in great part the data to determine the amounts and epochs of upheaval. Uplifting has been one of the prime factors of erosion, for it controls the declivity, velocity, and corrasive power of the streams, which in turn determine the amount of relief throughout the region; and the amount of relief is the chief factor which determines the rapidity and aggregate of erosion. Thus the entire range of facts presented in the geology and topography of this region are woven together, thread by thread, into a definite pattern of warp and woof. Volcanism, displacement, drainage, stratification, erosion, climate, each contributes its quota. To weave them together is no easy matter. Yet the region has had a history, and though its record is broken, disjointed, and scattered, we are still able to find many fragments and restore them to their proper places and sequence. The Uinkaret abounds in curious little facts, many of which, besides being instructive in themselves, are of great utility in piecing together this narrative. But their discussion must be reserved for a more deliberate and comprehensive work.

Before leaving the Uinkaret we may remark briefly that th Sheavwits Plateau, which lies to the west of it, is a region of much the same character. From the summit of Mount Logan it is well in view. Broad lava fields are spread over its surface, and these are all basaltic. One considerable volcanic pile stands upon its platform surrounded by younger craters and is named Mount Dellenbaugh. There are also several large buttes or broad mesas, upon its surface, composed of Permian beds capped with basalt, though the main platform is Carboniferous. The plateau, however, has been reconnoitered only and not minutely investigated. Upon its western verge is the Grand Wash fault, a gigantic displacement, where the whole country to the westward is dropped down between 6,000 and 7,000 feet. Upon the thrown side is found the Permian series complete in great force, and above it some of the basal members of the Trias. This fault is the boundary of the Grand Caon district and of the Plateau country itself. The region beyond is a sierra country, with the same characteristics as the Great Basin of Nevada and Western Utah.



1* It seemed to me, so far as could be judged from a distance, that a part of the faulting had been accomplished before the lava outflowed. The main fact, however, is clear that most of the faulting took place after the eruption, and of course settles the question of relative age or recency.
2* I would, if space admitted, be glad to describe the remarkable phenomena presented in the wall of the inner gorge directly across from Vulcan's Throne. Upon the very brink stands the remnant of an old crater (cinder-cone) which has been partially undermined and destroyed by the sapping of the wall-face. A lateral gorge sets back into the esplanade from the river to a distance of a mile or more. In the wall-faces are disclosed the dikes through which the lava came up. Their ?strike? is parallel to the course of the river, and perpendicular to the course of the Toroweap fault. Two of them protrude from the face of the wall about 600 to 1,400 feet below the summit; other protrude just at the brink. It is extraordinary that none are seen in the depths of the gorge. All of the attendant circumstances are surprising and curious, and yet it has frequently been noted that basalts habitually seek improbable places to erupt.
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