^B ' r- ■ HH *►• . •%■■>. ..», '• *•. ^b ■ /si. ■ H ■ ■ Digitized by the Internet Archive in 2011 with funding from Brigham Young University http://www.archive.org/details/reportongeologyoOOpowe 67418 GATE OF LODORE lie I DEPARTMENT OF THE INTERIOR. [J. S. GEOLOGICAL AND GEOGRAPHICAL SURVEY OF THE TERRITORIES. Second Division.— J. W. POWELL, Geologist in Chargk, REPO 11 T ON THE GEOLOGY OE THE EASTERN PORTION OF THE UINTA MOUNTAINS AND A REGION OF COUNTRY ADJACENT THERETO. WITH ^ T L ^ S . By J W. POWELL. WASHINGTON: GOVERNMENT PRINTING OFFICE 1870. PEEFACE. The region of country embraced in the map which accompanies this report is one of great geological interest, Three great categories of facts are here represented on a grand scale, viz: facts relating to displacement, facts relating to degradation, and facts relating to sedimentation. The dis- placements are of great magnitude, and because the beds involved are sedi- mentary strata but rarely altered, the characteristics of these displacements are plainly revealed, so that in our studies of them we have been able to arrive at conclusions, both quantitative and qualitative, with some degree of certainty. While displacement has been great, degradation has also been great, yet the country has not been planed down to a general base-level, but stands in mountain cliffs and escarped hills, where the strata are plainly revealed. The formations which we are able to study here have an aggregate thickness of 50,000 feet, and embrace groups of Paleozoic, Mesozoic, and Cenozoic Ages. Throughout nearly the entire region there is a condition of surface which renders the study of the geology comparatively easy. By reason of great altitude and extreme aridity the rocks are rarely masked by subaerial gravels, soil, or vegetation, and the book of geology lies open. We have thus been able to collect a large body of facts, which, in the fol- lowing volume, have been arranged in such order as it seemed would best present to the reader the general geology of the country. Many details have been omitted which would have been given bad the facts been pre- sented as they were collected in the form of an itinerary, but it was though that such a method would result in encumbering geological literature with a muss of undigested facts of little vnlue. Ill IV PREFACE. It may be well to indicate here the general routes of travel by which the country has been explored. In the fall of 1868 with a small party of men I crossed from the White River to the Yampa, and camped at the foot of Junction Mountain; thence I passed northward across the Snake River to the Pine Bluffs, and thence westward across Aspen Mountain to the Green River, and up the bank of that stream to Green River Station ; thence I crossed to Bryan, on Black's Fork, and down that stream to its mouth, then went south to the Cameo Mountains; thence eastward to Quien Hornet Mountain; thence to Flaming- Gorge, and from this latter point to Ashley Park, and from Ashley Park to Brown's Park. From Brown's Park I went through the Escalante Peaks, near the junction of the Yampa with the Green ; thence eastward past Junction Mountain to the White River. The course thus laid down is the general one of the pack train, but I myself branched from it in many ways. On this journey I first discovered the succession of Cenozoic and Meso- zoic groups, but did not divide the Upper from the Lower Green River, nor did I draw the plane of separation between the Upper Green River and Bridger Groups where I do now. Early in the spring of 18G9 I again crossed from the White River to the Yampa, camped at the foot of Junction Mountain, and spent a few days in the study of the adjacent region. I proceeded thence to Brown's Park, in which I camped for a few days, reviewing the geological studies of the previous fall. I then passed out of the park through Red Creek Canon, from its head, crossed the divide, and proceeded westward to the Green River, and camped again at Flaming Gorge for a few days. Thence I went up Henry's Fork, studying the region on my way, and crossed the divide to Fort Bridger. A few weeks subsequent I started on a boat trip to explore the lower Green and the Colorado River of the West. On my way I passed through the Uinta Mountains, stopping from time to time to make sections and to make geological studies of the country along the walls of the canons. Again, in 1871, I had a boat ride down the river. On this trip Mr. John F. Steward, of Piano, Illinois, was my assistant. We extended our studies on either side of the river for a distance of from ten to twenty miles. PREFACE. V In 1874, I started with a pack train from Green River Station, went up Little Bitter Creek, across Quien Hornet Mountain, through Red Creek Canon into Brown's Park; thence southeastward to the junction of the Snake River with the Yarnpa, where it was crossed; thence across the Yanipa Plateau to the foot of Split Mountain Canon, and thence to the Uinta Val- ley. Returning- from the Uinta Valley I visited the region drained by Ashley's Fork and Brush Creek, crossed the Uinta Mountains to the head of Sheep Creek, and returned to Green River Station. The course thus marked down was that followed by the pack train, which moved but slowly, usually resting two days out of three, while my own line of travel was in diverse directions from this general route. In 1875, I again started with a pack train from Green River Station, went east to Rock Springs and Salt Wells, thence south to the mouth of the Vermilion, thence to the eastern foot of the Dry Mountains, thence west through Brown's Park, past Flaming Gorge to the head of Sheep Creek, and thence through the Cameo Mountains to Green River Station. On this trip also the train moved slowly, and my studies were extended many miles in either direction from the general route. A few days later I made a trip to Salt Wells and Bitter Creek Stations, and particularly examined the region about Black Butte. The last part of the descriptive geology has been greatly condensed ; this is especially the case with the description of the structure of the Yampa Plateau, Junction Mountain, Diamond Peak, the Dry Mountains, Brown's Park, and the Aspen Mountain district. It was intended to illustrate the structural characteristics of these regions with a series of diagrams and sec- tions, but the plan was abandoned because the appropriation was exhausted. It was intended also to prepare a chapter on the physical features of the region, treating of the mountains, plateaus, monoclinal ridges, hills, parks, bad-lands, and alcove lands, and further treating of the three great kinds of drainage found in the region, viz, antecedent, consequent, and superimposed; but the necessity for immediate publication was so great that this plan has also been abandoned, and to this subject I hope to recur at a future time. On my travels during the year 1875, Prof. C. A. White was my geo- VI PREFACE. logical companion, and the trip was made largely for the purpose of collect- ing fossils at localities where they had previously been discovered, but to which sufficient time had not been given to make good collections. But many places of interest on account of geological structure were also visited, and I had the good fortune to have with me an experienced geologist on this my final review of the region ; and to Professor White, whose paper on paleontology appears in this volume, -I am greatly indebted. Nor must I fail to mention the valuable services of Mr. Steward; as he was with me in one of the earlier years of the work, and only in a portion of the region, his studies were but fragmentary, and the results have not been directly incor- porated in my general account of the geology of the country. I feel that I have not done him full justice in this matter, but the plan of publication would not permit the incorporation of his notes bodily; nor would such a course have done him justice, from the fact that a more extended study has greatly modified opinions entertained by both Mr. Steward and myself at that time. For the map I am indebted primarily to the labor and skill of Prof. A. II. Thompson, who has been my collaborator for many years, but in the work he has had several able assistants ; and in the year 1874, Prof. H. C. De Motte, of the Illinois Wesleyan University, traveled with me for the purpose of more thoroughly studying the details of the geography more distant from the river, and he somewhat extended the area of the survey embraced on the map. To Mr. Gilbert, I am indebted for great assistance in the preparation of the graphic representation employed in illustrating the Report, The diagram, Plate VII of the atlas, was prepared for me by Mr. Archibald R. Marvine. In the earlier years of my travels in the Rocky Mountain region, I studied to some extent the Park Mountains. Subse- quently the region was more thoroughly studied by parties under the direction of Dr. Hayden, and in his connection with that work Mr. Marvine traveled over much of the same ground that I had seen. It thus happened that we frequently discussed together the country which had been visited by both of us, and when I came to the preparation of this volume Mr. Marvine kindly proposed to construct this illustration for my use. This is PEEFACE. VII perhaps the last work done by Mr. Marvine ; at the time he was in very ill health, and a few days after sank into a condition from which he never recovered, and we now have to mourn the loss of a conscientious, able, and vigorous geologist, and it is with profound sorrow that I am compelled in acknowledging his courtesy to record his death. Mr. J. C. Pilling, for the past three years, has traveled with me as stenographer and assistant geologist, and to him I am indebted for the col- lection of a great body of details of diverse character, but especially in the measurement of many sections. Mr. W. Cleburn, one of the engineers of the Union Pacific Railroad, and who has been engaged in that work for many years, has at the same time interested himself in the geology and paleontology of the region, and to him I am indebted for many favors, and especially for the use of his valuable collection of fossils. To many of the citizens of the region I am indebted for courtesy and substantial favors, but especially to Capt, Pardon Dodds, of the Uinta Val- ley, and Mr. S. I. Field, of Green River Station. J. W. P. The following note from Professor White is inserted: Dear Sir : Since my report, comprising Chapter III of this volume, was put in type, further investigation of the fossils collected from the Canon of Desolation has led me to doubt the correctness of the reference I have there made of them to the Point of Rocks Group. It now seems probable that they properly belong to the Bitter Creek Group, notwithstanding the close relationship of two or three of the species with some of those found in strata that are still referred without doubt to the Point of Rocks Group. Further collections and investigations in the field will, however, be necessary before this question can bo definitely settled. Very truly yours, C. A. WHITE. Prof. J. W. Powell. V CONTENTS. CHAPTER I. THREE GEOLOGICAL PROVINCES. Page. Geographic characteristics of the three provinces 7 General characteristics of the sedimentary groups 8 Characteristics of orographic structure 9 Types of orographic structure 9 Orographic structure of the Basin Province 23 Orographic structure of the Plateau Province 25 Orographic structure of the Park Province 26 History of the three provinces duriug Ceuozoic time 32 CHAPTER II. SEDIMENTARY GROUPS OE THE PLATEAU PROVINCE. Tahle of the groups of sedimentary strata 40 Localities where the several groups can he studied 45 Section of White Cliff, Vermilion Cliff, and Shinarump groups ... 53 Uinta Mountain section 57 Cataract Cahon section 58 Grand Canon section GO Epochs separating the groups 62 Liguitic coal .73 CHAPTER III. INVERTEBRATE PALEONTOLOGY OE THE PLATEAU PROVINCE. Letter of transm ittal 74 General observations 75 Lower Silurian Age 79 Upper Silurian and Devonian Ages 79 Carboniferous Age 79 Mesozoic Age 80 Cenozoic Age 84 Catalogue of fossils 88 Carboniferous Age - ... 88 l ERRATUM. After « Chapter III, Invertebrate Paleontology of the Plateau Province," read, " By C. A. White, M. D." 2 CONTENTS. Page. Catalogue of fossils — Continued. Mesozoio Age , 92 Jurassic Period 92 Cretaceous Period 94 Cenozoic Age _ 102 Tertiary Period 102 Descriptions of new species 107 Carboniferous 107 Jurassic '. 110 Cretaceous 112 Tertiary 125 CHAPTER IV. GEOGRAPHIC DISTRIBUTION OF THE GEOLOGICAL FORMATIONS IN THE UINTA MOUNTAINS. Red Creek Quartzite 137 Uinta Group 141 The Carboniferous groups : 146 The Jura Trias groups 150 The Cretaceous groups 153 The Cenozoic groups 161 CHAPTER V. STRUCTURAL GEOLOGY. The eastern portion of the Uinta Mountains 176 Displacement 176 Degradation 181 Disintegration 182 Transportation 184 Scholium relating to the epoch of upheaval of the Basin Ranges 198 Sedimentation 198 The Yampa Plateau 202 Scholium relating to the terms " upheaval," " subsidence," &c 203 Junction Mountain 204 Diamond Peak « 204 The Dry Mountains 206 Brown's Park 208 Aspen Mountain district - 209 CHAPT E Ft I . THREE GEOLOGICAL PROVINCES. The Colorado River of the West drains a vast system of plateaus. On these plateaus are lone mountains, short ranges and groups of volcanic cones, and the principal affluents of the river have their sources in high mountains that stand on the rim of the great drainage basin. There is no considerable valley along the course of the Colorado River north of the thirty-fifth par- allel nor along the course of any of its principal tributaries. The streams run chiefly in deep canons which, with other important topographic features, serve to divide the area into plateaus. The district of country of which I thus speak is, in its important characteristics, a plateau region. This plateau character was well recognized by Dr. Newberry. In his report to Lieutenant Ives, page 41, he says: "The Colorado rises in a thou- sand sources at an elevation of from ten to twelve thousand feet above the sea, on the western side of the Rocky Mountains. Descending from their fountain heads, its tributaries fall upon a high plateau of sedimentary rocks which forms the western base of these mountains and occupies all the inter- val between them and the great bend of the Colorado River where the river enters the volcanic district already described;" and elsewhere in that vol- ume he makes frequent mention of these characteristics. Mr. Blake, in the third volume of the Pacific Railroad Surveys, Part 4, page 42, also mentions this topographic character as follows : "Extent of the table lands west of the Sierra Maclre. — This is a convenient point from which to take a general view of the broad expanse of the great plain that lies between the Sierra Madre and the mountains which form the 4 THREE GEOLOGICAL PROVINCES. eastern rim of the Great Basin. From the Sierra Madre up to this place the survey followed the eroded valleys of the streams, and the vision was bounded on both sides by their high and rocky banks, composed not only of the edges of thick horizontal strata, but often capped with the harder and more unyielding solid lava. The observer as he passes westward from the mountains is thus placed below the general level of the plateau, which does not become apparent to him unless he stands upon the top of the mesas and can thus cast the eye over the whole. The point already reached in the description is about half way between the Sierra Madre and the high mount- ains of San Francisco, and here, as we have seen, the upper strata of the plain are denuded and washed away, so that the banks of the streams are not so high, and the country appears more level or gently rolling. From this place the vision is unbounded toward the north, except by the horizon. The plain stretches far away, without any vestige of a mountain range. Indeed, it is the continuation of this plateau which rises upon the flanks of the Park and Wasatch Mountains at the far north, and through which the waters of Grand and Green Rivers cut their deep canoned channels. Farther south, these streams unite to form the great Colorado, which is also found traversing this grand plateau." Our studies of this great plateau region have not progressed so far that we are able to clearly define its boundaries, but these studies have shown that the region is complex topographically as well as geologically and is in fact composed of many tables. In this region the succession of sedimentary strata is unlike any series which has been studied elsewhere in North America ; different groups and different groupings of fossils are found; a different series of unconformities is observed and the displacements by faulting and folding have characteris- tics not commonly observed elsewhere. All these facts seem to warrant the conclusion that this plateau region should be considered as a distinct geologi- cal province, and in this brief report and others which are to follow I shall so consider it. A notice of its geographic connection with the surrounding country is needed. That portion of the United States west of the one hundredth merid- ian lies at a great altitude above the sea. The exceptions to this, as immedi- THE ROCKY MOUNTAIN REGION. 5 ately along the Pacific coast and the narrow valleys of some of the princi- pal streams, are but trivial. The rivers descend so rapidly from the upper regions that few of them are of value as highways of commerce; the valleys proper are narrow; treeless plains, cold, arid table lands, and desolate mountains are the principal topographic features. The more conspicuous of these are the mountains; lone mountains, single ranges and great groups of ranges or systems of mountains prevail. Owing to great and widely spread aridity, the mountains are scantily clothed with vegetation, and the indurated lithologic formations are rarely masked with soils, and the rocks, as they are popularly called, are everywhere exposed; hence all these mount- ains are popularly known as the Rocky Mountains. But there is more than one system of mountains, and later writers wishing to be more definite speak of the Cascade Mountains, the Coast ranges, the Sierra Nevada, the Wasatch Mountains, &c. But in an important sense the region is a unit; it is the generally elevated region of the United States; it is the principal region of the precious metals; it is the region without important navigable streams; it is the arid land of our country where irrigation is necessary to successful agriculture. But above all it is the rocky region; rocks are strewn along the valleys, over the plains and plateaus ; the canon walls are of naked rock; long escarpments or cliffs of rock stand athwart the country, and everywhere are mountains of rock. It is the Rocky Mountain region. There is a necessity for popular purposes for some general name and this one so appropriate will doubtless continue to be used, and it would seem best not to attempt to confine its application to any more restricted area ; but as our geographic and geological knowledge increases so that we are able to reasonably and appropriately define distinct ranges and systems of mountains within this great group, other distinctive names should be given to such ranges and groups. Influenced by this consideration, in speaking of the mountains that stand about the Plateau Province I shall use names for certain systems which seem appropriate to characterize them as distinct from other systems within . the great Rocky Mountain region. The eastern affluents of the Colorado River have their sources in the lofty mountains that stand as walls about the great parks of Southern Wyo- 6 THREE GEOLOGICAL PROVINCES. ming, Colorado, and Northern New Mexico, and these mountains constitute a system as well derined as we may hope for geographic systems to be de- fined by nature; and since my studies in that region in 1867-68, I have been accustomed to speak of them as the Park Mountains. The system is composed of many ranges, some well defined, others complex, inclosing, or nearly so, the North, Middle, South, and San Luis Parks, with many minor valleys and parks; and there are short outlying spurs and ranges with other parks and valleys. The principal mountain ranges are composed of meta- morphic rocks with unaltered sedimentary beds on their flanks. Some of the more western mountains are chiefly of this latter material, and many of the subsidiary mountains are of eruptive origin. Altogether they con- stitute a geological province characterized by a great development of meta- morphic crystalline schists with patches and structural basins of marine and lacustrine sediments, and a complicated series of vulcanic formations. Southward from the Oregon line, through Western Utah, Nevada, Southeastern California, and perhaps across the Colorado River in Western Arizona, many short and more or less distinct north and south ranges are found. The valleys and plains separating these ranges are covered with rather late subaerial gravels masking the underlying formations. The ranges are composed of metamorphic crystalline schists with Paleozoic beds on their flanks, or sometimes, even in large part of Paleozoic materials both complicated to a greater or less extent with eruptive beds; these eruptive beds themselves sometimes forming the principal component parts of the ranges. The little streams that have their sources in these mountains empty into salt lakes, or elsewhere their waters are lost in the sands; as it is popu- larly said they disappear in sinks. The most important of these is the Great Salt Lake, but there are many other basins without drainage to the sea. A few of the ranges are drained into the Colorado River. To this group Mr. G. K. Gilbert has given the name Basin Range System, which seems appropriate. It will be found convenient also to treat the area occupied by this group as a distinct geological' province. It has a series of sedimentary beds differ- ing widely from the Plateau Province; they are older, and the sediments of GEOGRAPHIC CHARACTERISTICS OF THE THREE PROVINCES. 7 the latter were in large part derived from the former. The Basin Province was the drv land that fed the sea and great lakes of the Plateau Province through a long period, while many groups, each thousands of feet in thick- ness, were deposited. Thus, for convenience of geological discussion, I speak of three great geological provinces — the Park Province, the Plateau Province, and the Basin Province — in order from east to west. The area included in these three provinces lies east of the Sierra Ne- vada and west of the Great Plains. In a general way the northern boundary is marked by the North Platte, with its proper upper continuation the Sweet- water River whose minute upper ramifications interlock with those of the Shoshoni River, which latter is a continuation of the northern boundary until it is crossed by the forty-third parallel of north latitude. When the region along the middle course of the Shoshoni River is more thoroughly studied, the Basin Range System may be carried much farther north than we are warranted in doing with our present knowledge; but I am inclined to the opinion, from the fragments of geological description which we have from that country, that another distinctly marked group will eventually be recognized here, having for one of its characteristics a great development of eruptive rocks. The southern boundary of the three provinces I am not able to clearly define. It may be well to state somewhat more categorically the characteristics, geographic and geological, on which I propose to divide this great area into three provinces. GEOGRAPHIC CHARACTERISTICS OF THE THREE PROVINCES. The Basin Ranges are short, more or less distinct north and south ridges separated by desert valleys which reveal broad stretches of sub- aerial gravels concealing the underlying formations. The general drainage is to interior salt lakes and sinks, but in the northeast corner there is a limited district drained by some small tributaries of the Shoshoni, and in the southeast there is a small district drained by the Rio Virgen into the Colorado River of the West. 8 THliEB GEOLOGICAL PROVINCES. The Plateau Province is composed of many tables bounded by canon and cliff escarpments. On these tables stand lone mountains, irregular groups of mountains, and short ranges. It is drained by the Colorado River of the West and its tributaries. The Park Province is characterized by broad, massive ranges, sometimes distinct, sometimes coalescing so as to include the great parks. The lofty peaks that serrate these ranges stand over snow banks that are perennial reservoirs for a multitude of streams whose waters on one hand are gathered into the Colorado River of the West, and finally discharged into the Gulf of Cali- fornia ; and on the other hand they are gathered into the Mississippi and the Rio Grande del Norte to be discharged into the Gulf of Mexico. Thus, in the three provinces, we have, first, desert valleys between naked ridges ; second, high plateaus severed by profound gorges ; and, third, massive, high mountains with shining snow fields. GENERAL CHARACTERISTICS OF THE SEDIMENTARY GROUPS OF THREE PROVINCES. The Basin ranges are composed of Paleozoic rocks with Eozoic schists below, and in the Humboldt Mountain district some Mesozoic and Cenozoic rocks are found. In the Plateau Province, Cenozoic and Mesozoic rocks prevail, though some of the important plateaus are of Carboniferous beds ; and in a few places deep corrasion has revealed still older Paleozoic and even Eozoic formations. The Park Mountains are chiefly Eozoic Since that age the region has been intermittently under the dominion of the waters, and Paleozoic, Mesozoic, and Cenozoic rocks are found at horizons » interrupted by gaps in the general series that are represented by dry land periods, while the last orographic agencies have left but fragments of these antecedent formations. T\PES OF OEOGEAPHIC STKDOTUEE. <) CHARACTERISTICS OF Tl'E OROGRAPHIC STRUCTURE OF THE THREE PROVINCES. TYPES OF OROGRAPHIC STRUCTURE. It seems convenient to give a general account of the types of oro- graphic structure in the region under consideration before characterizing each province by its special type. In this discussion I wish to use certain terms with a restricted or rela- tive meaning ; i. e., in treating of anticlinal and synclinal flexures I shall speak of those portions of the sedimentary beds which are adjacent to the anticlinal axes as having been upheaved, and those portions near their synclinal axes as having subsided. Again,, in blocks which are bounded by faults and tilted, I shall speak of such portions as are at a higher level as having been uplifted, and portions occupying a lower level as thrown. In such cases I do not wish to commit myself to any theory of upheaval or collapse in the change of the relation of the several parts of these beds to the center of the earth. In treating of the structure of the mountains under consideration it is necessary to distinguish two great classes, viz, those composed of sedimen- tary strata, altered or unaltered, and those composed of extravasated material. MOUNTAINS COMPOSED OF SEDIMENTARY STRATA L— APPALACHIAN STRUCTURE. The structure of the Appalachian Mountains, with closely appressed folds and axial planes tipped back from the sea, the modifications of these folds by faults, and the primary and concomitant forms of the mountains, have been clearly explained by the Messrs. Rogers and later writers, and have formed the basis of many discussions concerning geological dynamics. This Appalachian structure needs no further mention here, as it is a type of structure which so far has not been found in the region described above, and should it be found hereafter it will simply be an exceptional type to those known to prevail. 10 THREE GEOLOGICAL PROVINCES. II.— SIMPLE ANTICLINAL STRUCTURE. Mountains or short ranges carved from simple anticlinals are sometimes found, though this type of structure is not a prevailing one. Usually in such a case the great mountain mass lies in the central zone of the uplift. The fold is, of course, always found truncated by erosion, and the moun- tains represent but the difference between the amount of upheaval and the amount of such erosion. When not complicated by other types of structure the strata dip on all sides from the center of upheaval, gently or more abruptly, but the sides of the folds are never closely appressed. Such mountains in primary form are gently rounded in general outline, modified by the erosion of the streams running down their sides. Sometimes such 5. MILES. Fig. 1. — Section through Junction Mountain, north and south. East Fig. 2. — Section through Junction Mountain, east and west. B. P., Brown's Park ; S. C, Sulphur Creek ; J. T., Jura Trias; U. A., Upper Aubrey ; L. A., Lower Aubrey ; K. W., Eed Wall ; U., Uinta. mountains are severed by rivers running longitudinally, transversely or obliquely through them ; the rivers themselves having their sources in regions far away and passing through the mountains in their courses to the sea. In Northeastern Colorado a short distance above the junction of the Snake River with the Yampa, stands Junction Mountain, which serves as a UINTA STRUCT URE. H fine illustration of this type of structure. The mountain is divided iuto two unequal parts by a canon, through which the Tampa River runs. The axis of the mountain has a north and south direction. Figure 1 is ;i section through this mountain, in a north and south direc- tion, along the axis of upheaval. Figure 2 is a section through it in a transverse direction. CONCOMITANT FORMS. 1 . Monoclinal Midges on the Flanks. — Under conditions which are so well known as to need no further explanation here, monoclinal ridges or hog- backs are formed on the flanks of such upheavals, and sometimes such monoclinal ridges are of such magnitude as to be dignified with the name of mountains. Where two or more series of indurated, inclined beds are sep- arated by extensive series of softer material, two or more monoclinal ridges may be formed. 2. MonocHnal Itidf/es only. — Sometimes we find that an anticlinal up- heaval has been eroded in intaglio, so that there is no great central moun- tain mass, but the axis of upheaval is the site of a valley or low plain, but the monoclinal ridges on the flanks remain. 3. Inclined Plateau's. — Where the anticlinal upheaval has a great ampli- tude, as compared with the vertical uplift, the beds incline but slightly. Under such conditions inclined plateaus or mesas are found instead of monoclinal ridges, usually having steep escarpments facing the axis of the flexure. III.— UINTA STRUCTURE. . In the Uinta Mountains we have a great range carved from an anticlinal upheaval, the axis of which has an easterly and westerly trend, and is more than one hundred and fifty miles in length. It terminates abruptly against the Wasatch Mountains on the west and is cut off by the short, abrupt anti- clinal of Junction Mountain on the east, the latter having its axis in a north and south direction. There are several important facts observed in the study of this great flexure. Its axis has been lifted above the level of the sea about thirty thousand feet, and above the level of the adjacent country 12 THREE GEOLOGICAL PROVINCES. about twenty-live thousand feet. From flank to flank the flexure is about fifty miles, but varies much in width. We find on either flank, many miles from the axis, a line of maximum flexure, which line presents a subparallel- ism with the meandering axis. These lines have the effect of two mono- clinal flexures in opposite directions, separated by the broad table, diversified by elevated valleys and peaks of which the great mass of the Uinta Moun- tains is composed. But the portion between these monoclinal flexures or lines of greatest flexure is itself gently flexed. In many places that which I have called the line of greatest flexure is indeed a fault, in one place on the north side of the Uinta Mountains having a throw of twenty thousand feet. On the south side the line of greatest flexure is very irregular, being complicated in some places by faults having uplifts opposed to the down- throw of the flexure. On either side the great displacement is partly by faulting, partly by flexing, and either flank is a zone of diverse displace- ment where the strata are faulted, flexed, twisted and contorted in many ways. The character of these displacements in the Uinta Mountains is illus- trated in Plates 1, 2, and 3 of the Atlas, and in a subsequent chapter the subject will be more fully discussed. The simplest topographic forms produced by such displacements under7 conditions of erosion in general outline, are plateaus with gently rounded summits and abrupt shoulders on the flanks; but such general outline is often modified by the corrasion due to antecedent or superimposed drain- age; that is, by the corrasion of streams that head in remote regions and pass through these uplifts either longitudinally, transversely or obliquely, as in the case of Simple Anticlinals.* There are other modifications which sometimes greatly obscure the general topographic outline due to consequent drainage, i. e., the local drainage which is due to the upheaval itself and which produces inter- esting CONCOMITANT FOEMS. 1. Subsidiary Plateaus. — Sometimes the streams which head near the axis of such an upheaval, as they meander to the flanks, excavate valleys * For an explanation of what is meant by antecedent and superimposed drainage, the reader is referred to the Report on the Exploration of the Colorado River and its Tributaries, page 160, et scq. UINTA STRUCTURE— CONCOMITANT FORMS. 13 and divide the great block, which is a plateau in general outline, into minor plateaus which are separated by intervening but elevated valleys. This is especially the case where the streams in their upper courses follow for some distance the strike of the beds before turning to cross the more jor less abrupt lines of maximum flexure. Sometimes these streams run in deep gorges; in such cases the plateaus are bounded by cations. 2. Projecting Ridges. — When these consequent streams starting near the axis of upheaval take a somewhat direct course across the strike, the general plateau is cut into a series of sharp, abrupt ridges having a trend at right angles to the strike or general axis of upheaval. Thus the points of the ridges face the plain below and are separated by deep gulches and canons, and the observer on the plain below sees before him what appears to be a line of peaks separated by intervening gulches and valleys, and is apt to misunderstand the topographic character of the great mass which is before him. 3. Axial Peaks. — At some stages in the progress of erosion the channels of consequent drainage inosculate, and about their heads gorges are formed, with towering amphitheaters. In such cases an irregular line of crags and peaks will be found along the axis of upheaval. These I call axial peaks. 4. Flanking Peaks. — Sometimes we find a very hard bed or group of beds underlaid by more friable strata on a flank of the upheaval, which harder beds have been carried away by erosion from those portions of the upheaved mass nearer the axis. In such cases each projecting ridge is crowned with a true peak. I call these flanking peaks. 5. Interrupted Monoclinal Ridges. — On the flanks of these upheavals, but farther from the axis than the flanking peaks, monoclinal ridges are often found sometimes broken by gaps which are the channels of inter- mittent or permanent streams, and these ridges are very irregular and often interrupted. Where the downthrow is by simple flexure, a complete series is formed. Where it is partly by flexing and partly by faulting, some of the monoclinal ridges disappear. Where the faulting is on the side of the zone of maximum flexure nearest to the axis, the ridges of the 14 THREE GEOLOGICAL PROVINCES. upper beds appear ; but where the faulting- is on the side of the zone of maximum flexure farthest from the axis, the ridges of the lower beds appear; and where the displacement is chiefly or entirely by faulting-, there are no monoclinal ridges. IV.— KAIBAB STRUCTURE In the region under discussion we often find the sedimentary beds broken into great blocks by faults or their homologues, monoclinal flexures, and these blocks have been gently tilted in broad masses. I have dis- cussed this subject somewhat at length in my Report on the Exploration of the Colorado River of the West and its Tributaries, published in 1875 ; and in Figure 3 I reproduce a section and bird's eye view of the plateaus north of the Grand Canon, which was used in that volume. An examination of this will fully reveal the characteristics of what I have called the Kaibab structure. The grand topographic features which result from this structure are plateaus with broken edges where they are bounded by faults, flexed edges where they are bounded by monoclinal flexures, and with escarp- ments where they are bounded by canons or lines of cliffs. CONCOMITANT FORMS. •1. Cliffs of Displacement. — When a plateau is bounded on one side by a fault, the edge of the plateau is an escarpment often so abrupt as to present a more or less irregular line of cliffs. 2. Slopes of Displacement — When the displacement is a flexure rather than a fold, the edge of the plateau is a broken slope. I have discussed these cliffs and slopes of displacement somewhat at length in the volume already quoted several times, page 182 et seq. 3. Monoclinal Ridges on the Flanks. — On the flanks of these monoclinal flexures, under proper conditions which have already been described, monoclinal ridges are formed. 4. Monoclinal Ridges with Plateau Carried Aivay. — As in simple anticlinal upheavals the central mass may be entirely carried away leaving but monoclinal ridges, in like manner in the Kaibab structure the principal plateau mass may be carried away leaving only the monoclinal ridges. This I have also discussed in the volume already quoted. Paria Platean Virgin Vallev . Pine Valley Mountain I 1 ,1! fir M ii ••;•;■ UN \tit ■ ' - mm m si1 il:! V f .i ' J », MMM •IS 11 fin V ; i IV 1 I ' I ' f M || P ■• I I1 i' I--' I ! ' i '■ 'tip' n ; K)^ I'ari.i Fold. E«-Li. Cliffs. Marble Canon. East Kaibab Fold. Kaibab Plateau. "West Kaibab Fold. Kanab Plateau, Kauab Caiion. Kanab Plateau. To-ro'-weap Fault. TJ-in-karet Mountains. Hurricane Fault. Shi'.-wits Plateau. Grand Wash Fault, Grand Wash. s o ■a © ft 73 >-. O ^.2 35 SB a <° £° at 5-g o H c s KAIBAB STRUCTURE— CONCOMITANT FORMS. 15 5. Projecting Ridges. — It is seldom, perhaps never the case that the strata of one of these plateaus are left by the general displacement in a hori- zontal position ; but every block is tilted more or less, and often a valley appears at the foot of the slope, and the streams which head on the opposite brink of the plateau have excavated valleys, leaving- intervening ridges which project into the valley, having an effect somewhat like that described as one of the concomitant forms of the Uinta structure. 6. Cliffs of Erosion. — An inclined plateau may be bounded on the upheaved side by an escarpment of erosion, and such an escarpment is gradually carried back by an undermining process from the line of greatest upheaval. The drainage of such a plateau is usually from the brink of this escarpment toward the valley on the opposite side ; yet a minor drainage is found which carves out deep gulches, and the cliffs of erosion have deep reentrant and sharp salient angles. 7. Buttes. — Sometimes the gulches which form the deep, reentrant angles of a line of cliffs have lateral gulches, which by continued erosion coalesce, and the salient angles are gradually cut off from the escarpment, which is ever retreating. In this manner buttes are formed as outliers of cliffs. 8. Cameo Mountains. — Wherever considerable areas of horizontal or nearly horizontal strata are found sufficiently elevated above the base level of erosion, and such areas are drained by two or more subparallel water courses, the lateral drainage of these water courses will gradually inosculate in their upper ramifications, and, carving out deep channels, will leave behind mountains of horizontal strata. Such mountains are often of great beauty. This is especially the case where the beds are of different texture and color, when the mountains will be terraced and buttressed in beautiful regularity, and banded with the colors which are characteristic of the several beds of which they are composed. A few miles north of the Uinta Mountains, on the west side of the Green River, a group of such mountains are found, to which I have given the name Cameo Mountains, and I call this the Cameo structure. 16 THREE GEOLOGICAL PROVINCES. V.— BASIN RANGE STRUCTURE. When the blocks into which a district of country has been broken by faults are greatly tilted so that the strata dip at high angles, the uplifted edges of such blocks often form long mountain ridges. Such ridges have the general appearance of the monoclihal ridges already described as con- comitants of other types of structure ; but in this case the ridges constitute the chief mountain masses themselves, and form .another general structural type. The monoclinal ridges are due to the erosion of upheaved strata ; these ridges are due to displacement; they may also be eroded, but in so far as erosion has progressed the ridge like structure is obscured. Many of the rido-e like mountains of the Basin Province have this structure. Such a ridge is composed of monoclinal strata, the one side presenting a bold escarped front, the other a more gently sloped back conforming to a greater or less degree with the dip. Sometimes the ridges themselves are faulted longitud- inally, transversely or obliquely, and the faults may be slight or of great magnitude ; but the more common structure is a simple ridge with slight transverse or oblique faults. CONCOMITANT FORMS. 1. Monoclinal Ridges on the Back. — On the backs of these Basin ranges monoclinal ridges have been observed. VI.— ZONES OF DIVERSE DISPLACEMENT. In this region many zones or irregular areas of country are found to be divided into small blocks by faults and flexures running in diverse direc- tions, and these may be horizontal or be tipped at high or low angles, or even be overturned. The total effect of this diverse displacement may be to uplift the area above or depress it below the adjacent country or not to change its relative altitude. These features are exhibited on a small scale within a limited area, usually so elongated as to be termed a zone. During the past season Mr. Gr. K. Gilbert has studied an area where this diverse displacement is by faulting, and the faults are of no great magnitude, and the blocks into which the area has been severed are either not tilted or but slightly so. This presents the simplest illustration of this type that has N Fig. 4— Bird's-eye view of a portion of the Musinia Zone of Diverse Displacement, The area represented is six miles square. The base line shows the sea-level. The tract is drained by Salina Creek, which unites its branches in the center and flows through the canon on the left. IT Fig. 5,-Deduced from Fig. 4. A restoration' of the displaced rocks as they would appear had there been displace- ment but no degradation. ZONES OF DIVERSE DISPLACEMENT. 17 yet been discovered. It is simply the Kaibab structure on a very small scale. Fig. 4 is a bird's eye view of the blocks mentioned. In the section, in the foreground, the heavy line represents the summit of the highest Cre- taceous group. Fig. 5 is a diagram of the same region showing the blocks into which it is severed, and the same restored to the condition they would have, had there been no denudation. On the south side of the Uinta Mountains, and east of the Green River, another comparatively simple area has been studied by myself. This zone of diverse displacement is on the flank of the great Uinta upheaval. These displacements are chiefly by flexures rather than by faidts, and the blocks are more tilted and contorted than in the last, In Atlas, Plate No. 4, we have a stereogram representing these displace- ments, and in a subsequent chapter the subject will be more fully discussed. Y">ii'"-"-"" ' "' A.— Siiiiplo Anticlinal displacement. B.— Uinta displacement. E a rmzmnuzm 0. — Kaibab displacement. E D. — Basin Range displacement. ..-'■'■j f— — -"1 E. — Zone of Diverso displacement. Fig. 0. — Types of Displacement. Many other areas far more complex than these have been discovered where a zone has been broken into blocks, and these blocks tipped and contorted in diverse ways and directions like the blocks of ice crowded in an eddy of a northern river at the time of its spring flood. The topographic features found in such areas are zones of irregular hills. 2 p G Figure 6 is a IS THREE CEOLOGICAL PROVINCES. diagram illustrating the general types of displacement heretofore discussed. A represents a Simple Anticlinal displacement ; B a Uinta displacement ; C a. Kaibab displacement ; 1) a Basin Range displacement ; and E a Zone of Diverse displacement. MOUNTAINS COMPOSED IN WHOLE OR IN PART OF EXTR/V- VASATED MATERIAL. We are not able in the present state of our knowledge to draw legiti- mate conclusions concerning the relation of the eruptive rocks so widely distributed through all three of these geological provinces, but the following types of structure have been observed. VII.— TABLE MDUNTAIN STRUCTURE. We often find beds of sedimentary strata preserved from erosion by a capping of lava. Such are usually called table mountains; the underlying strata may be horizontal or inclined. Earlier stages of this structure are seen in mesas or low tables, and sometimes in valleys or gulches which have been filled with extravasated material, and erosion has proceeded to a limited extent on either side of these harder masses carrying away the softer sedimentary material and leaving the harder volcanic rocks in the midst of the valley, and this may have an elevation lesser or greater than that of the adjacent country beyond the rim of the valley. A fine example of a table mountain is found in Pilot Butte, in AVyo- ming Territory. VIII.— U1NKARET STRUCTURE. Simple sheets of lava may be poured into a valley or on a plain, and "serve as a protection to the sedimentary beds which are immediately under- lying them and, as the erosion of the adjacent country not thus protected progresses, new vents may be formed along the edges of such sheets and at a lower level. Still erosion progresses, and still new floods of lava arc poured out, and still at lower levels, until a mountain is left behind with its central mass composed of sedimentary material, but covered on the summit TU-SIIAR STRUCTURE— VOLCANIC STRUCTURE. 19 and flanks with irregular and overlapping patches of lava. Thus lava bed is imbricated on lava bed, but unlike the tiles of a roof, the upper edge of the lower sheet is placed on the lower edge of the upper. This struc- ture is well represented in the Uinkaret Mountains in Northern Arizona, and has been more fully discussed by me elsewhere, vide The Exploration of the Colorado River, &c, page 1 99 et seg. IX.— TU-SHAR STRUCTURE. When a plain or valley which receives extrav^ated material from below remains at a base level of erosion during the period of successive eruptions, flood of lava is piled on flood of lava until a vast mass of material is accu- mulated from which the rains and streams carve mountains. The several beds of which such a mountain mass is composed are exceedingly irregular, from three causes: first, each bed as poured out was an irregular mass, due to its degree of fluidity and the character of the ground on which it was poured; second, each bed was more or less modified by erosion, which occurred after it was poured out, and before it was covered by a subsequent flood; and, third, the general mass has been eroded to a greater or less ex- tent in producing the present forms. The volcanic activity being in a region where movements of displace- ment are in progress, it is often the case that the structure of this class of mountains is greatly modified by such displacements. Mountains composed of such irregular beds of lava are of frequent occurrence in the region under discussion. A fine example is seen in the vicinity of the town of Beaver, Utah Territory, in what are known as the Tu-shar Mountains. X.— VOLCANIC STRUCTURE. When many eruptions come successively from the same vent, and each is a comparatively small amount, cones are built. Cones of such simple structure are of frequent occurrence in the region under discussion. Great complex cones such as are found in other parts of the world do not occur, but a few double and one triple cone has been observed. The great majority of the cones observed are built of cinders on broad sheets of lava, and are in fact concomitant forms of lava mesas. Such cones are comparatively ephem- eral, as the scoria and ashes of which they are composed yield readily to atmos- 20 THREE GEOLOGICAL PROVINCES. pheric degradation. Where .such a cone exists, still having a well defined crater, its condition testifies to the lateness of its origin, and all the facts relating to the sheet of lava on which it rests fully corroborate the conclu- sion. From such evidence we are able to infer the recency of much of the volcanic activity in the three provinces. If the human history of America could be carried back to as early a date as it has been in Asia, it cannot be doubted that the earlier chapters of that history would be replete with the accounts of volcanic fires. XI— HENRY MOUNTAIN STRUCTURE. Sometimes we find the sedimentary strata displaced by a quaquiversal upheaval and the same fractured, and through these fractures floods of lava have poured, and these may lie in patches about the flanks of the mount- ains, or stand in dikes where the walls of the crevice have been swept away by denudation. In the Henry Mountains we have a fine illustration of this type of structure. These mountains have been studied by Mr. Gilbert during the past season, and in his preliminary report he says : " The erup- tions of the Henry Mountains are of a character entirely novel to me, and they were studied with an interest stimulated by surprise. A description of a single one, though it will not stand for all, will serve to illustrate the type. Mount Ellsworth is round, and its base is six or eight miles broad. The strata of the plain about it are horizontal on every side. Near the mountain the level strata become slightly inclined, rising from all sides toward the mountain. At its base the dip steadily increases until on the steep flanks it reaches a maximum of forty-five degrees. Then it begins to diminish, and the strata arch over the crest in a complete dome. .But the top of the dome has cracked open, and tapering fissures have run out to the flanks, and they have 'been filled with molten rock, which has con- gealed and formed dikes. Moreover, the curving strata of sandstone and shale have in places cleaved apart and admitted sheets of lava between them. So the mountain is a dome or bubble of sedimentary rocks with an eruptive core, with a system of radial dikes, and with a system of dikes in- terleaved with the strata. It is a mountain of uplifted strata, distended and permeated by eruptive rock." * * * * * * TYPES OF MOUNTAIN STRUCTURE. 21 In the foregoing characterization of certain types of structure found in these regions, I have not attempted to adopt a system of exact classifica- tion, which should be both inclusive and exclusive as the types do not admit of such classification. No " hard and fast lines " can be drawn. I have simply attempted to indicate the important types with their primary and concomitant forms. It is manifest that the structure of a sedimentary mountain will depend primarily upon two elements — the type of the displacement and the char- acter and extent of erosion. The erosion may be antecedent or superim- posed, or it may be consequent, or these methods may be combined, and the erosion may be modified by dip, texture, and other characteristics of the beds producing- concomitant forms. For convenience, I subjoin the following : SYNOPSIS OF THE TYPES OF MOUNTAIN STRUCTURE RECOGNIZED IN THE FOREGOING DISCUSSION. MOUNTAINS COMPOSED OF SEDIMENTARY STRATA, AL- TERED OR UNALTERED. I.— APPALACHIAN STRUCTURE. (Not found in the three provinces.) ■ II.— SIMPLE ANTICLINAL STRUCTURE. Primary topographic form. Plateau with rounded vertical outline. Concomitant forms: 1. Monoclinal Ridges on the Flanks. • 2. Monoclinal Ridges only. 3. Inclined Plateaus. HI.— UINTA STRUCTURE. Primary topographic form. Plateau with rounded summit and abrupt shoulders on the flank. 22 THREE GEOLOGICAL PEOVINCBS. Concomitant forms : 1. Subsidiary Plateaus. 2. Projecting- Ridges. 3. Axial Peaks. 4. Flanking- Peaks. 5. Interrupted Monoclinal Ridges. IV.— KAIBAB STRUCTURE. Primary topographic form. Plateau with angular outlines. Concomitant forms : 1. Cliffs of Displacement. 2. Slopes of Displacement. 3. Interrupted Monoclinal Ridges on the Flanks. 4. Monoclinal Ridges with Plateau Carried Away. 5. Projecting Ridges. 6. Cliffs of Erosion. 7. Buttes. 8. Cameo Mountains. V.— BASIN RANGE STRUCTURE. Primary topographic form. Monoclinal ridges of displacement, Concomitant forms: 1. Monoclinal ridges on the back. VI.— ZONES OF DIVERSE DISPLACEMENT. Topographic form. Irregular hills. MOUNTAINS COMPOSED IN WHOLE OR IN PART OF EX- TRA VASATED MATERIAL. VIL— TABLE MOUNTAIN STRUCTURE. VIII.— UINKARET STRUCTURE. IX— TU-SHAR STRUCTURE. X.— VOLCANIC STRUCTURE. XL— HENRY MOUNTAIN STRUCTURE. l/ MONOCLINAL IlIDGES. 23 OROGRAPHIC STRUCTURE OF THE BASIN PROVINCE. In this province that orographic typo which I have described as the Basin Range structure prevails. In the consideration of the structure of these ridge like mountains, it is necessary to distinguish clearly the two more important elements involved, viz, that of the metamorphic and unaltered sedimentary formations, and that of the eruptive beds. The former appear in simple monoclinal ridges of displacement, but the extravasated material may occupy any position in relation to the simple ridges ; sometimes it is found appearing on the flanks, sometimes burying portions of the ranges, sometimes extending in subequal masses in trans- verse or oblique directions to the ridges proper, and in many ways compli- cating the topographic structure. It is of the' structure of the monoclinal ridges only that I now speak. These ridges are not residuary fragments of anticlinal flexures eroded in intaglio, for wherever the structure at the foot of the escarpment is not concealed by subaerial gravels, the beds seen at the summit of the ridge, or known to belong to a still higher horizon, appear again at the foot of the escarped face, showing that they have been thrown to that position by a fault. The ridges themselves occupy the place of max- imum upheaval. In the summer of 1870 I had some opportunity to examine a few of these ridges while on a trip from Salt Lake City to Fillmore, Bea- ver, and Saint George, in Utah. In the winter of 1871-72, I spent a few weeks studying the mountains west of the Rio Virgen, and again in 1873 while engaged in prosecuting some ethnographic studies I visited many points in Western Utah, Nevada, and Southern California, making cursory examinations of mountain structure on my way; but Mr. G. K. Gilbert, while engaged as geologist of the Wheeler expedition, made a much more thorough study of this region. In his report of the geology of that region for 1872, and published in 1874, page 50, under the head of "Mountain Building,"' Mr. Gilbert presents a "diagram of generalized mountain sections discounting denudation,1' which I reproduce (Fig. 7), preserving his lettering. 24 TIIIIEE GEOLOGICAL PROVINCES. In explanation of the diagram Mr. Gilbert remarks: "The sections accumulated by our geological observers admit of the following1 classifications : B C D E F Fig. 7. "1. Faulted monoclinals occur, in which the strata on one side of the fault have been lifted, while those on the opposite side either do not appear (A), or (less frequently) have been elevated a less amount (B). Two-thirds of the mountain ridges can be referred to this class. "2. Other ridges are uplifts limited by parallel faults (C), and to these may be assigned a few instances of isolated synclinals (D), occurring under circumstances that preclude the idea that they are remnants omitted by denudation. "3. True anticlinals (E) are very rare, except as local, subsidiary fea- tures, but many ranges are built of faulted and dislocated rock masses (F), with an imperfect anticlinal arrangement. "Not only is it impossible to formulate these features, by the aid of any hypothetical denudation, in such a system of undulations and foldings as the Messrs. Rogers have so thoroughly demonstrated in Pennsylvania and Vir- ginia, but the structure of the Basin Range system stands in strong contrast to that of the Appalachians. In the latter, corrugation has been produced commonly, by folding, exceptionally by faulting ; in the former, commonly by faulting, exceptionally by flexure. In the latter, few eruptive rocks occur; in the former volcanic phenomena abound, and are intimately associated with ridges of upheaval. The regular alternations of curved anticlinals and syn- clinals of the Appalachians demand the assumption of great horizontal dimi- nution of the space covered by the disturbed strata, and suggest lateral pressure as the immediate force concerned; while in the Basin Ranges, the displacement of comparatively rigid bodies of strata by vertical or nearly vertical faults involves little horizontal diminution, and suggests the appli- cation of vertical pressure from below." Thus a characteristic range of this country is the edge of a great block OROGRAPHIC STRUCTURE OF TIIE PLATEAU PROVINCE. 25 upheaved by the production of a fault and pari passu with the upheaval, eroded into irregular forms and modified by flows of eruptive matter from beneath. While this is the general structure throughout the region under consideration, there are many exceptions, as indicated by Mr. Gilbert. Of especial interest are the "uplifts limited by parallel faults (C), and to these maybe assigned a few instances of isolated synclinals (D), occurring under circumstances that preclude the idea that they are remnants omitted by denudation," and the "many ranges built of faulted and dislocated rock- masses (F) with an imperfect anticlinal arrangement." Perhaps the latter are what I have called Zones of Diverse Displace- ment. In the northern portion of the province other modifications of the gen- eral structure seem to appear. Mr. King, in the third volume of the "Geo- logical Survey of the Fortieth Parallel," page 431, says: "These low mount- ain chains which lie traced across the desert with a north and south trend are ordinarily the tops of folds whose deep synclinal valleys are filled with Tertiary and Quaternary detritus." That there should be exceptions to the general type of structure in this province is not strange, for similar exceptions occur in each of the other provinces, as will appear hereafter; but I have myself seen no true anticlinal mountains in the Basin Province. The mountains of eruptive origin in this province are chief!)' accessory masses to the simple ridges of upheaval, and so far as my observations extend, are of the Tu-shar type. OROGRAPHIC STRUCTURE OF THE PLATEAU PROYIXCE. In the Plateau Province the Kaibab structure prevails, but other types of structure are found. The Uinta Range, which furnishes the type for the Uinta structure is found within this province, and a number of simple anti- clinals have been discovered ; we have also found man}' Zones of Diverse Displacement. The mountains of eruptive origin are of all the types above mentioned ; table mountains have been observed in the region drained by the Grand, White, and Yampa Rivers. Pilot Butte has already been mentioned, and \ 26 TIiEEE GEOLOGICAL PROVINCES. Other mountains of this type arc found in the Sevier district The Uinkaret Mountains, which have been tqken as a type of structure, are on the north side of the Grand Canon of the Colorado. San Francisco Mountain and other mountains in that vicinity are known to be of this structure, but this great group of mountains, of which San Francisco Mountain is the culmi- nating- peak, has not been sufficiently studied to enable us to characterize them. The Navajo Mountain, Sierra la Sal, and others in this region are known to be of the Henry Mountain type. The principal number of important peaks and great mountain masses of the Plateau Province are divided about equally between the last two classes. Some mountains of the Tu-shar structure are found in the Sevier district, Volcanic cones are found in great numbers throughout the south- ern portion of the province. OROGRAPHIC STRUCTURE OF THE PARK PROVINCE. The great mountain masses of the Park Province, especially those to the north standing about the South, Middle, and North Parks, which I have myself seen, are composed of metamorphic crystalline schists. It would appear that these schists were metamorphosed antecedent to the deposition of the Paleozoic, Mesozoic and Cenozoic rocks, which are found in many places resting unconformably upon them ; for all these later sedimentary beds contain to a greater or less extent conglomerates which are composed of fragments of metamorphic materials resembling those of the principal mountain masses ; and it further appears from my brief studies that this series of rocks was profoundly plicated, perhaps on the Appalachian type, i. e., with closely appressed folds, and this also prior to the deposition of the upper sediments. Through Paleozoic and Mesozoic times minor changes of level have occurred, now lifting the area above the sea, now submerging it, ■ so that many gentle unconformities are found with an interrupted succes- sion of sedimentary beds. But the last great orographic displacements are represented by broad upheavals which appear to have the structure of the Uinta Mountains, so far as can be made out from the fragmentary evidence left by the great erosion to which the country has been subjected Mil. MARVINE ON THE PARK RANGE. 27 in fete geological times. The plateau like structure of these great ranges with sedimentaries dipping at high angles on their flanks, sometimes recurved so as to cause inversion of the succession of strata, was a feature which made a deep impression upon me in my travels through this country some years ago, and in my imagination I continued the later sedimentary beds in high curves over these plateaus, and dimly conjectured that tens of thousands of feet had been eroded from some of the ranges, and that the table or plateau like character of the janges was due to some epoch of this later denudation of the ranges when they were planed down to a common level under conditions which I have explained in the volume several times quoted. Such a planing down occurs when the channels of the eroding streams remain for a great length of time at a general base level. But when I came to study the Uinta Mountains it seemed to me that all the facts which I had observed in the Park Province were duly explained by sup- posing that that province had the same structure as that observed in the Uinta Mountains. Since my stud}' of that country Mr. Arch. R, Marvine has made a much more thorough and careful survey of it as one of the members of Dr. Hayden's corps. In the report of the United States Geo- logical and Geographical Survey of Colorado, 1873, Hayden, on page 188, Mr. Marvine, under the head of " Blue River or Mount Powell Group ", says : " The Park Range, after its abrupt rise from the broad rolling ridge at the north, entirely changes in its characters. It appears to be a rectangu- lar shaped mountain mass cut into the most profound amphitheatral headed gorges, which are separated by the most rugged and sharp saw-like ridges of rock imaginable. The main ridge lies along the southwestern side of the mass, and from it the valleys and their sharp separating ridges trend in a general northeast direction. The northernmost spur was composed of a very distinctly and evenly bedded series of schists, gneisses, and granites which had a strike nearly with the ridge, and a dip of 40° or 50° to the southward. Looked at from the east, the general impression is received that all of the lavge ridges of the range have a similar structure. These rugged ridges, in their easternmost portions, present a pretty uniform gen- eral elevation, and as the northern ridge expands at its end into an even- surfaced table-like mass of rock, the impression is given that all of these 28 THREE GEOLOGICAL 'PROVINCES. . sharp ridges are but the remnants left from the cutting' away of a plateau like step which once followed along the mountain face. These ridges also end quite similarly along a pretty straight line, and descend to rather a uniform level. Regarding now more particularly the northern ten or fifteen miles of the high range, which includes but four or five of the ridges, it is observed that at the base of each steep end the lowered spur does not con- tinue on as a sharp ridge but slopes off, a flat surfaced, plateau like area, descending gently eastward. Sincer upon the corresponding area at the base of the northernmost ridge, great quantities of debris of the Lower Cretaceous sandstones were found, abundantly proving that they covered the area, it appears that all of these flattish areas either are now, or have comparatively recently been, covered with the same sandstones. Such features would seem to indicate that the Cretaceous had once extended hiffh up, or quite over the whole range, and that the latter, in its upfolding, had received the most pronounced uplifts along certain well-defined lines, the intervening portions not being tilted up at high angles. It is by such a process that the front range, at least from the Big Thompson to the South Platte, has received much of its uplift. Major Powell and Mr. Gilbert have noticed similar folds in the Kaibab Plateau and adjacent regions on the great Colorado Plateau of Northern Arizona, though there the sedimentary beds have not (by many a thousand feet) been stripped by erosion from off the underlying rocks. It is a form of mountain building which I think is not uncommon in the West." I am inclined to think that the purposes of orology will be better sub- served by classing this structure as a type distinct from that of the Kaibab structure, rather than as a modification of it. The general arching of the strata between the lines of maximum flexure or faulting, allies it some- what to a true anticlinal ; and so far as my studies go these lines of great- est flexure have many more complexities than the faults and monoclinal flexures usually found in the Plateau Province. Hence I have classed it as a distinct type and called it the Uinta structure. We already know that the spaces between the broad upheavals, of which the ranges themselves are composed, are complicated by many anti- clinal and synclinal flexures and by many faults, but the whole structure of 67418 STRUCTUBAL CHARACTERISTICS OF THREE PROVINCES. 29 the parks, as these interspaces are often called, is exceedingly complex, and much study is necessary, and a great accumulation of facts must be obtained before any safe generalization can be made ; but these interspaces or park areas are sometimes Zones of Diverse Displacement. Atlas Plate No. 6 presents a section across three of the great ranges of the Park Province. This section has been prepared for me by Mr. Marvine. The scale on which it is drawn does not admit of great detail, but the gen- eral orographic cliaracteristics are well represented. In a single section it is impossible to present all of the facts upon which this generalization is based. In the quotation from Mr. Marvine already given some of the facts on which his opinions are based appear, and I have myself seen patches of sandstone high up on the Front Range in the vicinity of Long's Peak, and also on the northern end of the Park Range' in an area of country not visited bv Mr. Marvine, but the shreds of evidence are too multifarious to be assem- bled here. The park spaces between the great ranges are seen to be com- plex in the section, but the full extent of this complexity could be illustrated only by the most full and graphic representation. Doubtless when the reports of the several members of the First Division of the United States Geological and Geographical Survey of the Territories are published, the general structure of this country will be more fully revealed. I have quoted Mr. Marvine and discussed this subject with him more fully from the fact that he and I have visited many of the same points. I have not myself studied the eruptive mountains of this province, y SUMMARY OF THE STRUCTURAL CHARACTERISTICS OF THE THREE PROVINCES. The Basin Province is characterized by north and south ranges that are monoclinal ridges of upheaval, and these monoclinal ridges are separated by- stretches of subaerial gravels that mask the structure of the areas of subsi- dence. But while this is the prevailing structure, other types are found. In the Plateau Province the Kaibab structure is the characteristic. Here on a grand scale the primary and concomitant forms are found; but 30 THREE GEOLOGICAL PROVINCES. Simple Anticlinals, the Uinta structure, and Zones of Diverse Displacement are found as exceptional types. In the Park Province the Uinta structure prevails and its primary and concomitant topographic forms are grandly shown. Doubtless a more thor- ough study of this region will result in the discovery of exceptional types. THESE PROVINCES NOT SEPARATED BY WELL DEFINED LINES. No line of demarcation can be drawn between the Plateau Province and the Park Province. There is an irregular belt of country separating the better defined portions of the two provinces, which is complicated by characteristics belonging to each. The Kaibab structure of the plateaus does not change abruptly into the Uinta structure, which prevails in the latter province. In fact there are many areas lying along the border sepa- rating the two provinces which are characterized by a great development of eruptive beds, which serve to a greater or less extent to mask the oro- graphic structure of the sedimentary beds. In like manner on the south and west of the Plateau Province there is a belt of country separating it from the Basin Province, itself forming a sub- province of great interest, This region has already been the subject of much .study, and although these studies have not been completed, many facts have been discovered from which we can with safety make some important de- ductions. Through late Mesozoic and earlier Tertiary times there was an old shore line here, now retreating eastward, now advancing westward. It is a region of many movements by faulting and flexing, and during these movements, in Tertiary times at least, many lavas were poured out, so that we have many unconformities both abrupt and gentle, many shore deposits, many faults and flexures and many beds of eruptive matter. But the north- ern portion of the Basin Province is separated geographically as well as geologically from the Plateau Province by the Wasatch Mountains which constitute a distinct geographic system; but geologically it is but a northern extension of the intervening belt which I have already described, charac- terized as distinct from that by the fact that the movements of displacement — ZONES OF DIVERSE DISPLACEMENT. 31 faulting and Hexing — were on a grander scale and as a consequence of this greater displacement, the accumulations of sediments are greater and the unconformities more apparent and complex. Another consequence of the greater displacement is that the deep lying metamorphic rocks are brought up and exposed by denudation, so that extensive groups of crystalline schists and quartzites appear. This geographic district, the Wasatch Subprovince, terminates on the south at Mount Nebo, and is quite distinct geographically as well as geologi- cally from the subprovince to the southward, which may be termed the Sevier and Rio Virgen Sub-province. Thus the Wasatch and Sevier districts separate the Basin and Plateau Provinces, not by the introduction of new types of structure, but by a com- bination of the types observed on either hand and being1 complicated by conditions consequent on their forming- for a long- time the shore line be- tween the two. In the Sevier portion of the belt the Kaibab structure pre- vails, while in the Wasatch portion the Basin Range structure prevails. The great Wasatch Range presents a bold front to the west due in a general way to a great fault or rather a series of faults such as I have de- scribed as occurring in the Basin Ranges; but on the east or back slope of the range the structure is complex. An irregular belt of country stretching from the crest of the mountains eastward many miles is faulted and flexed in many ways. In the northeast angle formed by the Wasatch and Uinta Mountains there is a long but narrow and irregular zone stretching toward the north- east from the head- waters of the Bear River. Sulphur Creek drains a part of this, and the well known Bear River coal lands are found in the district. From Aspen to a point near Carter, the Union Pacific Railroad runs along the eastern border of the belt. Its extension in either direction beyond the points indicated are unknown to me. This belt also exemplifies what I have called Zones of Diverse Displacement, and the general effect is upheaval. The belt seems to have been broken into very irregular blocks by lines of faulting or flexure which so far as my observation has extended preserve no law of direction. The blocks into which the country has been broken have been tilted, 32 THEEE GEOLOGICAL PROVINCES. greatly sometimes, sometimes turned quite on edge, and even in some cases reversed. One of these blocks standing- on edge afforded Professor Meek the opportunity to make his section on Sulphur Creek published in Dr. Hay- den's Report on the Geological Survey of Montana, Idaho, Wyoming, and Utah, 1872. Professor Meek evidently recognized the difficulty of correlat- ing the strata in that section with those outcropping elsewhere in the dis- trict. I mention these excessively complex zones without attempting to explain them. Some student of geology will eventually find here a subject rich in results. SUMMARY OUTLINE OF THE HISTORY OF THE THREE PROVINCES DURING CENOZOIC TIME. % In the latter part of Mesozoic time the greater part of the Basin Province was dry land. The Plateau Province was an open but shallow sea. In the Park Province a chain of islands extended to the south. The Cenozoic time was inaugurated by a series of movements, which, continued to the present time, have produced the topographic features now observed. This part of the crust of the earth, and I mean by the term "crust" simply that portion of the earth which we are able to study by actual observation in truncated folds and eroded faults — this portion of the crust, then, was gradu- ally broken and contorted. The Plateau and Park Provinces were cut off from the sea, and great bodies of fresh water accumulated in the basins, while to the east in the region of the Great Plains, in earlier Tertiary times at least, there was an open sea. Slowly through Cenozoic times the outlines of these lakes were changed, doubtless in two ways: first, by the gradual displacement of the rock beds in upheaval and subsidence here and there ; and, second, by the gradual desiccation due to the filling up of the basins by sedimentation and the erosion of their barriers ; and the total result of this was to steadily diminish the lacustrine area. But the movements in the dis- placement extended over the Basin Province, for that region was then a comparatively low plain, constituting- a general base level of erosion to which that region had been denuded in Mesozoic and early Tertiary time when it was an area of dry land ; for I think that from the known facts we may reasonably infer that the Basin Ranges, though composed of Paleozoic THE THREE PROVINCES DURING CENOZOIC TIME. 33 and Eozoic rocks, are, as mountains, of very late upheaval. For some pur- poses, and in broad generalization, erosion furnishes a valuable measure of geological times. A mountain, as a mountain, is comparatively ephemeral. The evidence of this is found on every hand as we study the Rocky Mount- ain region. There can be no conclusion reached from reasoniii"- on geological data more certain than that the Uinta upheaval began at the close of Mesozoic time, and has continued intermittently near to the present, and during that time this upheaval has suffered a degradation in areas of maxi- mum erosion of no less than 30,000 feet; and there is evidence also which leads to the conclusion that the conditions for great erosion were not per- sistently maintained during this time. I have already stated that the Basin Ranges occupy the area of maximum upheaval, and they are monoclinal ridges. Had these ridges been upheaved - greatly beyond their present altitudes it is manifest that erosion would have carried them far back from the lines of faults, a condition not found to obtain. In the erosion of these ridges, as an independent subject of study, the geologist is impressed with the magnitude of the work which has been per- formed by atmospheric agencies. It appears that each ridge is but a small residuary fragment of the great inclined block, and the interrange spaces are filled with clays, sands and gravels, the waste of these blocks, in such a manner as to bury the underlying rocks over broad areas ; and whether we consider the amount which has been lost from the blocks or the amount which has been accumulated in the valleys, the loss here or the gain there, this transferred material is very great. It is worthy of remark that over much of the area, the deposit of this transferred material in the valleys was subaerial, but in the northwestern portion of the province it was lacustrine. But when we compare the erosion which these inclined blocks have suffered with that of many of the great blocks in the Plateau Province of the Kaibab structure, or with that of the Uinta uplift, or with the great uplifts in the Park Province, the erosion of the Basin Range ridges sinks into insignificance. And when we consider, further, that the erosion in the Plateau and Park Provinces which we are able to study has all been per- formed during Cenozoic time, and that the conditions of maximum erosion were but intermittent during that time, we are forced to the conclusion that 3 P G 34 THREE GEOLOGICAL PROVINCES. the conditions for great erosion now found in the Basin Ranges have existed but for a short period, i. e., the blocks were certainly not upheaved ante- cedent to Cenozoic time ; and it would seem probable that it must have been in late Tertiary. It seems proper to add here a remark concerning certain conditions of erosion, though I have elsewhere discussed the subject more fully. The lesser or greater rapidity of erosion depends chiefly upon three conditions : first, elevation above the base level of erosion ; second, the induration of the rocks ; and, third, the amount of rain fall. But erosion does not increase in ratio with the increase of the precipitation of moisture, for increasing moisture serves to increase the protection derived from vegetation. Nor does induration greatly preserve rocks from erosion, for on most exposures the action of the elements in disintegrating the rocks is in excess of the power of the streams to carry the material away. The exceptional exposures are found on steep slopes; yet the difference in the induration of beds has an effect as seen in the minor or concomitant forms of all mountain regions. The principal factor in maximum erosion is elevation above the base level, and the power of erosion increases in geometric ratio with the elevation. The power of the streams to transport the material of erosion is increased in geometric ratio and the power of the water in corrasion is in like manner increased ; and the corrasion of deep channels by rapid streams filled with sands, gravels and bowlders produces another condition of surface favorable to general degradation — that is, the walls of these deep channels are broken down by gravity, which is further increased by an undermining process where harder and softer beds alternate. With these facts in view, we need not enter into a consideration of the difference of texture or indu- ration of the rocks of the Plateau and Park Provinces and those of the Basin Province; but we may remark that of the 30,000 feet eroded from the Uinta uplift, more than 1G,000 feet were of beds of Paleozoic Age, and with a texture as firm as the rocks of the Basin Ranges. It is manifest that the result of all these movements of displacement in the three provinces was general upheaval. But this upheaval in the three provinces was unequal; it was great in the Basin Province, greater in the THE DRAINAGE REVERSED. 35 Plateau Province, and greatest in the Park Province. The Basin Provhn e was already above the sea level, but a comparatively low plain. In such a condition, erosion would be slight ; and as the ranges were lifted, the mate- rial derived from them was deposited in the valleys, and it is probable that no considerable amount was transported beyond the province into the sea, and the general uplift of the province was little or no greater than the change from that of the low plain near the sea level to its present elevation — that is, the Basin Province as a body is not the result of the difference be- tween erosion and elevation ; but the ranges themselves do thus mark the difference between erosion and elevation. That which was taken from the mountains was added to the valleys. Much of the Plateau Province was still an area of rapidly accumulating sediments long into Tertiary time ; but at last the movements which began at the commencement of Tertiary time succeeded in bringing the whole area not only above the level of the sea, but above the general level of the Basin Province itself; so that while the Basin Province Avas drained into the Plateau Province in earlier Tertiary time, in late Tertiary time the drainage was reversed, and the streams of the Plateau Province found their way to the sea by passing through the Basin Province, and many of them, especially those in the Sevier and Wasatch regions which head along the old shore line, are now drained into the basins which characterize the province thus designated. It is the opinion of Mr. Howell, and I believe also that of Captain Dntton, that this drainage was in some cases reversed along the very channels occupied by the ancient streams which ran from the Basin Province into the Plateau lakes. In the Park Province the general upheaval was still greater, and the Colorado River, which empties into the Gulf of California, heads in the very heart of the Park Province and drains the greater part of the Plateau Province by carrying its waters across the Basin Province. While the general surface of the last two mentioned provinces Avas in Mesozoic time not above the level of the sea, at the present time the general surface is from four to fourteen thousand feet above the sea level ; but there are portions now marked by great ranges which have been upheaved twenty and thirty thousand feet ; but these portions during the progress of upheaval suffered denudation, and a part at least of the material thus denuded was 36 THREE GEOLOGICAL PROVINCES. not carried away to the sea but was deposited in fresh water basins. But at last these fresh water basins themselves were drained and their beds faulted and flexed and eroded, and their sites are now found marked by broad stretches of bad-lands. I speak of an open sea to the east of the Park Mountains, where now the Great Plains stretch in broad expanse. That there was a sea or arm of the sea here is manifest, for I have collected marine Tertiary fossils of Vicksburgh types in several places east of Denver; but from my exceed- ingly brief studies in that region, merely as a passing traveler, I can only say that the region, though simple in its topographic features, is indeed complex in its geological structure. Throughout this great area, from the eastern slope of the Park Moun- tains on the east to the eastern slope of the Sierra Nevada on the west, and from the sources of the Green and Shoshoni Rivers on the north to the San Francisco Mountains on the south, the whole region is broken, flexed, and contorted along innumerable lines. But the great structure lines have a north and south trend ; the ranges of the Basin Province run from north to south ; the great faults of the Plateau Province also run north- and south, and the Park Ranges have a north and south trend. But these general outlines are broken by oblique and transverse displacements, usually of a minor magnitude, though in some cases, as in the Uinta Mountains, these transverse displacements assume as great proportions as the north and south flexures and faults. While the whole region is exceedingly complex by displacement, it is also exceedingly complex by reason of the unconformity of its sedimentary beds. And all this complexity is greatly increased by reason of the floods of lava which have been poured out here and there over the entire area, and now and then through Cenozoic up to the present time. And all these floods of lava, all these thousands of eruptive moun- tains, thousands of mesa sheets, thousands of volcanic cones, testify to a period of great volcanic activity while the region was in fact a great conti- nental area, thus contradicting the generalization which has obtained in some quarters that volcanic activity is adjacent to the sea. And further, very much of this volcanic activity has been exhibited since the desiccation of the lakes. CHAPTEE II. SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. We turn now to a consideration of the Plateau Province. Throughout its extent it is traversed by profound gorges or canons ; high cliffs are found ; long ridges and lone buttes are seen, all presenting escarpments unclad with vegetation where the geological structure is plainly revealed, and it is nowhere concealed to any important extent by subaerial gravels, river deposits, deep soil, or rich vegetation. The whole region has been flexed and faulted on a vast scale ; the flexures are truncated by erosion, and the faults are crossed by canons and lines of cliffs ; and tlms by a combination of circumstances the whole region is an open book to the geologist, revealing a wonderfully complicated structure and a grand succession of formations. Accumulations of sediments may be studied of Cenozoic, Mesozoic, and Paleozoic Ages, each represented by formations that are measured by thou- sands of feet. In tlje hearts of the mountains and depths of the canons Eozoic rocks are found ; on the mesas and elevated valleys sheets of lava have been spread; and naked volcanic cones crown the geological series. A general section of the sedimentaiy beds alone sums up a total of nearly 60,000 feet, and the relations of the groups into which they can be divided can be determined with a certainty rarely attainable in the eastern portion of the United States. When we group these beds in such a manner as the structural geology demands we have a series of groups or succession of formations separated by epochs of change, producing unconformities or resulting in extensive stratigraphic peculiarities, and in constructing a gen- eral section of this country this natural series cannot be ignored without 37 38 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. greatly distorting the facts. But a section thus arranged presents a series of limestones, shales, sandstones and conglomerates totally unlike that which has been established in the New York and Appalachian Province or in the Valley of the Mississippi. Again in several of the groups we dis- cover the remains of rich faunas and floras, but the series of fossils belonging to any of the natural groups in the Plateau Province is unlike that of any group or formation in the earlier studied rocks of the east ; either entirely new series are found or the old types are regrouped so as to present a new aspect. Hence it would be manifestly absurd to introduce into this newly studied province the nomenclature adopted in those provinces which had been previously studied, as' it would involve the necessity of explaining in each case that the name was used with a new meaning, and that the adop- tion of the older names was intended simply to express the opinion that the group to which it was given should be referred to some period in the geo- logical time scale about the same as that held by the group to which the name was originally applied ; and this would involve the re-adjustment of the names from time to time on the. collection of new suites of fossils. While it does not seem possible to consider a particular sandstone or limestone, or a particular group of strata as identical with or closely similar to one in New York or Illinois, this does not preclude the possibility of establishing a general synchronism. The Cenozoic, Mesozoic and Paleozoic Ages seem to be as well defined as elsewhere, and in each age there are formations which are earlier or later, but the details of this general synchronism can only be discovered after a far more thorough study of the paleontology of the province has been made. The conclusions thus stated have been reached after a study of the province which has occupied the greater part of the last eight years. During the earlier years I attempted here to find the formations of the east, or at least formations corresponding to them, and thus years of -study were in part fruitless for that reason. I then determined if possible to discover the natural series of the province itself independent of other regions, and the general section below is the result. Perhaps, from a priori reasons, I should have commenced with this plan. The supposi- tion that at the same time sediments should have been carried into the NAMES OF THE GROUPS. 39 Colorado sea similar to those in the New York sea, is not warranted by a study of the deposits now forming- in existing seas. The Hudson River carries a very different deposit into the Atlantic Ocean from that carried by the Colorado River into the Gulf of California. Nor should we expect that the faunas or floras of regions so widely separated should be the same or closely similar. In the earlier times, which we study as geologists, there seem to have been physical conditions in the two regions as widely differing as those of the present. The Cenozoic formations of the plateaus are lacus- trine ; the Cenozoic formations of the Atlantic slope are marine. The Meso- zoic of the plateaus is of great extent and thickness, while that age is but scantily represented on the Atlantic slope. Nor do the Paleozoic forma- tions exhibit a close similarity. The names which I have selected for the groups are geographic, as such a system admits of easy interpolation, and the localities serve well in fitting the name to the group and refer* at once to the typical strata. For obvious reasons I should have been pleased to have commenced with a clean slate, selecting such localities as would serve for the best types ; but I did not feel at liberty to ignore the labors of geologists who had pre- ceded me. In the Cenozoic groups and the first Mesozoic I found great confusion, as these groups had been seen at many places, and some of them received several names each ; and often different groups were confounded by being included under one geographic name. With these groups I have tried to select such localities as would serve to fairly represent the groups and at the same time do no injustice to other laborers. We now append the general section. 40 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. TABLE OF THE GROUPS OF SEDIMENTARY STRATA OF THE PLATEAU PROVINCE. Scale in loot. O 0 •> ° V Q * ' °J " a <£s- Q r *> *? O «*»0 O %<> UN 1,800 2,000 5C0 BOO :i, 000 1,800 1,800 2,000 501 Groups. i'.OO | Bishop Ml Conglomerate Brown's Park. Bridger. Upper Green Rivei Unconformable by plication and erosion wiiii uiiderlyiua ruck.*. Sandstones, gravels, limestones, concretionary and stratified flints. Unconformable with ail underlying rocks. Bad-land sandstones, (chiefly green-sands,) lime- stones, shells — marls, and concretionary and Stratified fliuts. Lower Green Rive) Bitter Creek. 'lain beds Tower landatone Sandstones, sometimes argillaceous, and limestones, Carbonaceous shale* and ugoitic coal near middle.* A massive or irregularly bedded BajldstOfle, ferrugi- nous. Unconformable by erosion with lower group. Shales, often bituminous ; sandstones and lime- stones ; carbonaceous shales and lignitic coal near the base. Bad-land sandstones, often with much gypsum ; indurated sandstones; ferruginous; sfaell- marls ; many beds of carbonaceous shales and lignitic coal. To the southward the group is composed of indurated sandstones and lime- stones. Unconformable by plication and ero- sion with tin- next. Point of Bocks. Upper Hogback Sandstone. Middle Hogback Sandstone. Golden Wall Sandstone. Sandstones, usually indurated, sometime ferruginous, with many beds of carbonaceous shales and lignitic coal. Salt Wells. Sulphur Creek. Henry's Fork. Sandstones or arenaceous shales ; often very friable, producing bad-lauds, wilh carbonaceous shales and lignitic coal. Black shales; occasionally friable sandstones with carbonaceous shales and lignitic coal. Sandstones, bad-land rocks, conglomerates and shales, with carbonaceous shales and lignitic coal. * Unconformable by erosion with the nest. TABLES OF TIIE GROUPS. 41 w 1 H n M M H o 2 O fc < 3 f this group ; th* upper is cherty limestone from 100 feet to 200 feet in thickness. which we have called the TJellerophon Lime.-lone. The lower, the Yampa Sandstone, is very massive, rarely showing evidences of stratitica ion; in some places obliquely laminated. Farther southward cherty limestones prevail, and the whole group is more minutely stratified. Sandstones and limestones massively bedded or shaly. Tn s~nio localities sandstones prevail and aic exceedingly friable. Chiefly limestones. In the Uintft Mountains massive limestones are separated by thin strata of sandstones. In the Grand Canon a massive limestone a thousand feet in thickness is found, with thinner strata of limestone and sandstono beneath. In the Uinta Mountains the group is conformable with the Le- dore series and unconformable with the Uinta Sandstone. In the Grand Canon it is conformable with the Tonto Group. Lodorc. Sandstones and shales : supposed to be the equivalent in the Uinta Mountains to the Tonto Group in the Grand Caiion. Uinta. Sandstones; massive; thinly bedded, and shales; ferruginous; some portions metamorphosed, becoming a quartzite. Uncon- formable by extensivo plication and erosion on the Red Creek Quartzite. 42 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. A quartzito with horublcndic and micaceous schists, all greatly implicated. TABLES OF THE GROUPS. 43 BASE OF THE SECTION IN THE GRAND CANON OF THE COLORADO. 2, 000 4,0C0 6,000 8,000 10,000 I-', 000 14,0 0 - Sandstones and shales, with a lew limestones; uncon- formable by extensive plication and erosion on the next. Rase of Red Wall Group. Sandstones, shales, and a, few limestones. On further study this "roup will probably bo subdivided. Uornblendic and micaceous schists and slates, with beds and dikes of granite. Thickness unknown. Found at the bottom of the Grand Canon. 44 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. REMARKS CN THE GENERAL SECTION. The thicknesses which I have given in the table are considered to be nearly an average. Many of the groups are much thicker in some places, and thinner in others. If the maximum thickness of each had been given, the sum would have been more than 70,000 feet; while if the 111111111111111 had been given the sum would have been reduced nearly to 50,000 feet. The Mesozoic and Paleozoic sediments in all latitudes where they have been studied, are found to attenuate as you pass from the western to the eastern border of the province. In characterizing the rocks I have attempted to give only those features which are general throughout the province so far as it has been studied ; but there are many local peculiarities which we have observed and which will appear in the detailed reports. LOCALITIES WHERE THE SEVERAL GROUPS CAN BE STUDIED. I now append a«few localities where these several groups can be seen under favorable circumstances. They might be multiplied greatly, but perhaps no good purpose would thus be served. BISHOP MOUNTAIN CONGLOMERATE. The Bishop Mountain Conglomerate can be seen on the summit of Bishop Mountain, where it lies unconformably on the eroded beds of the Bitter Creek Group. A fine exposure can also be seen on the summit of the Quien Hornet Mountain. brown's park group. This group is well represented at Brown's Park, in Northeastern Utah and Northwestern Colorado. A good section can be obtained in the high bluffs on the west side of the Snake River by commencing about five miles above its confluence with the Yampa where these beds are seen to rest unconformably against Car- boniferous strata at the foot of the mountain. In going north two minor flexures are passed where the upper members of the group are exposed ; and, on reaching a third and greater upheaval, the group is exposed fi-om summit to base, and is seen to rest unconformably upon Bridger beds. LOCALITIES WHERE THE GROUPS CAN BE STUDIED. 45 15RIDGHR GROUP. This group can be well studied in the vicinity of Fort Bridger, at Church Buttes, and in the Cameo Mountains. It has an extensive development in this region, i. e., west of the Green River and north of the Uinta Mountains, and is usually well exposed. An outlying patch can be seen between Vermilion Creek and the Snake River, on the north side of the Dry Mountains. It can also be finely studied at Haystack Mountain. UPPER GREEN RIVER GROUP. The Plant Beds of this group are well exposed to the north of Green River Station, and between that point and Alkali Stage Station in many gulches and canons. They are also well exposed in the cuts of the Union Pacific Railroad between Green River Station and Bryan. Another good exposure can be seen in the escarpments on either side of Henry's Fork, commencing about five miles above its mouth and continuing up the stream for several miles. The Tower Sandstone is well shown in the cliffs at Green River Station and in that vicinity, especially up and down the river for several miles. This sandstone is also well exposed on the eastern side of the Green River, below the mouth of Currant Creek. LOWER GREEN RIVER GROUP. This group is well exposed along the Green River from Green River Station southward for ten miles where a detailed section has been made and will be given hereafter. It is also well exposed in many of the escarp- ments of the Quien Hornet Mountain. We again find it well exposed in the escarpments a few miles northeast from the head of Vermilion Canon. Fine exposures are seen on the Snake River six miles above the northern foot of Junction Mountain. The elevated ledges known as Pine Bluffs, near the sources of the eastern tributaries of Vermilion Creek, are capped with the limestones and bituminous shales of this group. BITTER CREEK GROUP. This group is well exposed along Bitter Creek in the vicinity of Bitter 46 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. Greek and Black Buttes Stations. A fine section can be obtained by com- mencing- at Pine Bluffs at the foot of the limestone beds and passing in a direction a little north of west until the massive gray sandstone of the next group is reached. Across this stretch of country the beds dip to the east, and their outcropping edges stand in a succession of ledges and can be well studied. It is better to follow the line which I have indicated than to make a section along Bitter Creek, as there is a fault passing between old Hall- ville and Black Buttes Station, and it is difficult along that line to determine the amount of the fault, and hence there is a liability of duplicating or omit- ting some of the lower members of this section. This fault will be explained hereafter. The junction of the Bitter Creek Group with the Lower Green River can be very well seen in the escarpment at Pine Bluffs; one hand can be placed upon a limestone of the upper group and the other on a massive bad- land sandstone of the lower. In like manner the junction between this group and the next lower can be well seen in an escarpment east of and facing Black Butte. There is an escarpment on the northeast side of Bitter Creek, facing that stream and extending from Hallville Section House to Point of Rocks, where the upper sandstones of the Point of Rocks Group stand in an almost vertical cliff, and the lower members of the Bitter Creek series can be seen to rest upon this sandstone unconformably. These beds are exceedingly friable, ferruginous sandstones and shales, and in many places a shelf or terrace is seen between the foot of the Bitter Creek shales and the brink of the cliffs formed of the Point of Rocks sandstone. This group can be studied along the Union Pacific Railroad west of Rock Springs. Three-fourths of a mile east of Lawrence Section House the railroad passes with an abrupt curve around a ledge of rocks, where the junction of the Bitter Creek series and the Lower Green 'River can be plainly seen. Here you may place your forefinger on a limestone of the Lower Green River and your thumb on a bad-land sandstone of the Bitter Creek Group. In the escarped hills on either side, the line between the limestones and buff and pink sandstones can be plainly seen. These rocks dip to the west at an angle of about four degrees, and as you go eastward this dip gradually increases, and bed after bed of the Bitter Creek Group can bo seen well ex- LOCALITIES WHERE THE GROUPS CAN BE STUDIED. 47 posed by passing back and forth among- the hills until reaching a point about a mile and a half west of Blair's coal mine, you come to a high ridge or hogback where the series ends. This hogback is composed of the* upper sandstone of the Point of Rocks Group; the junction of the two groups on this line can be very well seen. The gray sandstone of the Point of Rocks Group is massive and indurated. The brown, ferruginous shales of the Bitter Creek Group yield readily to atmospheric degradation, and have been swept away back of the ridge or hogback, leaving broad, naked surfaces of gray sandstone. Another fine section can be obtained by commencing on the southern face of the Quien Hornet Mountain and passing over the escarped ledges in a southwesterly direction along the blnifs of Red Creek until you reach the foot of the great hogback which is composed of beds of the Point of Rocks Group. Vermilion Creek in its upper course runs through beds of this group. Its many wet-weather tributaries have carved the country with deep but flaring channels, and the naked beds can be seen on every hand; and the bad-land hills are rilled with fossils; but the lower members of the group cannot well be studied by reason of some complicated but interesting dis- placements that are observed a little north of the Vermilion Canon. These displacements will be discussed hereafter. To the southward this group of rocks is developed over broad areas. The Canon of Desolation for much of its course is cut through these rocks, and in its high walls this group can be studied to advantage. The Pink Cliffs of Southern Utah are of this age. POINT OF ROCKS GROUP. A good section of this group can be obtained at Point of Rocks Station. There is a series of cliffs and abruptly escarped hills extending from a point northeast of the station in a westerly direction for several miles. These escarpments face Bitter Creek and the Union Pacific Railroad. In the cliff immediately back of the depot at Point of Rocks the junction between the Bitter Creek and Point of Rocks Groups is well seen. As I have already described, the lower members of the upper groups are brown, friable, arena- 48 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. ceous, ferruginous shales, with occasional beds of soft sandstone, all weath- ering easilv; and the line of junction between that and the massive gray sandstone which forms the summit of the Point of Rocks Group can be plainly seen. In these shales immediately overlying- the massive sandstone there are beds and seams of coal. The first massive sandstone is the Upper Hogback Sandstone. These rocks all have an easterly dip, and as you go westward you soon reach the base of the Upper Hogback Sandstone, then pass the beds of irregularly bedded shales and sandstones until you reach a second massive, gray sandstone., which in many places is broken into two or more beds. This is the Middle Hogback Sandstone. Still going west- ward, massive and thinly bedded sandstones of yellowish-buff color alter- nating with massive beds of light gray or white sandstone, are seen. About six miles from the station the railroad turns southward and debouches from the narrow canon valley of the Point of Rocks into the broad open valley of the Salt Wells. To reach the base of the Point of Rocks Group it is necessary to diverge from the railroad, which passes along the foot of the cliffs, and continue in a westerly direction until the last massive gray sandstone is reached. It will then be noticed that the massive beds, both yellow and gray, have been passed, and that another series of more thinly laminated beds underlie the massive series. These alternating beds of gray and buff belong to the Golden Wall Group. The separation between these two groups at this point is not as plainly marked as at many other regions. The whole thickness at this locality is about 1,800 feet. When Messrs. Meek and Bannister made their section along this line, or their Point of Rocks Section, they commenced a few hundred feet below the summit of the group and ended about 300 feet above its base, which was not seen by them; for in turning southward with the railroad they crossed two great faidts having their throw to the north. The lines of fault- ing pass along a valley showing no rock exposures, and when they passed out into Salt Wells Valley they were on beds of the Salt Wells Group at a horizon of six or eight hundred feet below the summit. Another good section of this group can be obtained at Rock Springs. A few hundred yards west of the mineral spring known as Rock Spring, a great, massive sandstone stands in a ledge, the beds dipping to the west at LOCALITIES WHERE THE GROUPS CAN BE STUDIED. 49 an angle of about 1G degrees. The brown shales and sandstones of the upper group have been stripped from this sandstone over broad areas, and the junction between the two can be plainly seen. Starting from this point and going eastward, a series of gray sandstones above, interrupted by car- bonaceous shales and beds of coal, are passed; then gray and buff sand- stones are seen until the Van Dyke Mine is reached. A little east of this point we come to the base of the Point of Rocks Group, and reach the summit of the Salt Wells Group. I have never examined this point with sufficient care to enable me to indicate the exact junction, but as described in the Point of Rocks Section above, the junction is not very well denned. Fine sections can be obtained on either side of the Green River two miles above Flaming Gorge where this group of beds was measured and found to be 2,00') feet in thickness. Here they stand, on edge, and their stratification can be well seen. The foot of Desolation Canon, and Gray Canon on the Green River affords another fine section, and the group can be well studied in the Wa- satch Cliffs at the head of the Escalante River, and in the hills at the foot of the Pink Cliffs, in Southern Utah. SALT WELLS GROUP. Standing south of the debouchure of the Point of Rocks Canon into Salt Wells Basin, and looking eastward, lines of cliffs and escarped hills are seen. Climbing these hills until the first massive, light gray sandstone is found, you reach the summit of the Salt Wells Group and the base of the Point of Rocks. Then, turning westward you descend from this eminence, and still continuing in a westerly direction you pass along the foot of an escarpment which faces the railroad, the beds of which dip at an angle of about 8 degrees to the east, and hence you are passing from higher to lower strata. Still continuing in this direction for several miles, and crossing the broad valley of Pretty Creek, you reach at last the axis of the upheaval near Baxter Section House. Here we find an escarpment facing the north, the rocks of which are light colored, arenaceous shales above and dark, argillaceous shales below. The arenaceous shales are at the base of the Salt. Wells Group; the black shales below are believed to belong to the 4 P Cx 50 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. summit of the next group. No examination of the section has been made along this line nor have the beds been studied in detail, but the upper and lower limits of the group are tolerably well defined. On the Green River, about two miles and a half above Flaming Gorge, the junction between the black shales of the lower group and the yellow shales of the upper can be well seen, and the junction between this group and the Point of Rocks Group is also well seen. Here the beds stand on edge and were measured, and a thickness of nearly 2,000 feet obtained. This group can be •well studied in narrow zones along the northern flanks of the Uinta Mountains. Fine exposures occur in the Pink Cliffs and at Gunnison's Butte on the Green River south of Gray Canon, and north of the point where that river was crossed by Captain Gunnison on his trip to Utah in 1853. SULPHUR CREEK GROUP. This group of black shales can be well seen in the hills near Billiard Station on the Union Pacific Railroad. Here Sulphur Creek cuts through them for several miles. In Professor Meek's u Section on Sulphur Creek near Bear River," his "No. 1" is the summit of the group. The locality does not present a good type from the fact of the great displacements to which the beds have been subjected. Their relation to underlying beds can- not be determined with certainty; but on the north and south sides of the Uinta Mountains many fine exposures are found. I have already mentioned the point where the junction of this group with the overlying can be seen, north of Flaming Gorge ; the beds dip to the north at an angle of nearly 90 degrees, and on the south side of Henry's Fork the junction of the black shales with the next group is plainly seen. Here the beds were measured and found to be 2,050 feet in thickness. Farther eastward between the head of Dry Lake Valley and Vermilion Creek the beds dip to the north at an angle of about 25 degrees and are truncated with the great Uinta flexure. Still farther south in the Escalante Valley, Paria Valley, Kanab Valley and many other localities, the entire group is well exposed. henry's fork group. This group can be well studied at the typical locality which is on the LOCALITIES WHERE THE GROUPS CAN BE STUDIED. 51 south side of Henry's Fork, commencing about two miles above its mouth and extending for many miles to the westward. These beds stand on edge and are well exposed. Their junction with the black shales can be plainly seen and the base of the group is the second conglomerate below the teliost shales; the teliost shales themselves constitute a conspicuous datum point ' from which to study the stratigraphy of this district. Many sections can be obtained on either side of the Uinta Mountains. Perhaps no better place can be found than on Ashley's Creek, where the group stands in a hogback near Dodd's Ranch. Many other localities could be mentioned on the Price, Escalante, Dirty Devil, Paria and Kanab Rivers. FLAMING GORGE GROUP. This group can be well studied at the typical locality, viz, in the vicin- ity of Flaming Gorge. Commencing at the conglomerate above mentioned as forming the base of the Henry's Fork Group, you pass southward over the upturned edges of the beds, crossing the bad-land sandstones, then the Mid-group Limestones, then the bad-land indurated sandstones, until the White Cliff Limestone is reached. The massive, cross-bedded sandstones beneath, is a very conspicuous feature of the landscape, and forms the sum- mit of the next group. In mentioning the typical and other localities of the foregoing groups I have not given detailed sections, as in a following chapter, on the descrip- tive geology of the Uinta Mountains and adjacent country, it will be neces- sary to describe more minutely the stratigraphy of all these groups. These typical localities excepting that of the Sulphur Creek Group all fall within the area that is to be described. The typical localities of the remaining or loAver groups are without the region described in this volume, and hence I shall give sections of the groups as they occur at the typical localities. WHITE CLIFF GROUP. The locality selected as representing the typical series of this group is in Southern Utah. Here a long irregular escarpment or line of cliffs is seen facing southward, from which the geologist may overlook two other sub- parallel lines of cliffs and see in the distance the walls of the Grand Canon 52 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. of the Colorado. The Paria, Kanab and Rio Virgen, with their many tribu- taries that head in the Pink Cliffs above and to the north, have cut many canons and canon valleys through these escarpments, and here the structural geology and stratigraphy are plainly revealed; not only of the White Cliff Group but also of the Vermilion Cliff and Shinarump Groups. The sec- tion which I shall give of these three groups was made along the course of the Kanab in the winter of 1871. The escarpment known as the White Cliffs presents to the mid-day sun a bold wall of pure white or golden sandstone reflecting its rays with a shim- mering, brilliant light. At such a time the traveler toiling over the and sand- dunes below, sees before him to the east or west a long stretch of pink and vermilion hills — hills of shifting sands, with no promise of spring or brook at which his thirst may be quenched; the precipice of the Vermilion Cliffs to the south, and the White Cliffs a wall of fire to the north. A more con- spicuous or well defined topographic feature could not well be imagined. On top of the wall and usually a little back from the edge the lime- stones which form the base of the Flaming Gorge Group is seen. This lime- stone has been traced from point to point along the intermediate country for the entire distance from Flaming Gorge to the White Cliffs. The following is a section of the White Cliff, Vermilion Cliff, and Shina- rump Groups from the base of these limestones to the summit of the Upper Aubrey Group. LOCALITIES WHERE THE GROUPS CAN BE STUDIED. 53 Fig. 9.— SECTION OF WHITE CLIFF, VERMILION CLIFF, AND SHINARUMP GROUPS. 10 iv^<< ,',-•:.:-: .v t> o*e c c o o o* IK i^'yQ^.-'o''* WHITE CLIFF GROUP. No. 1, 600 foct. Light gray or white .sandstone ; massive ; cross-bedded. i No. 2, 300 feet. Bright pink and vermilion sandstone ; cross-bedded. No. 3, 200 feet. Gray, red, and brown sandstone ; cross-bedded ; of many colors ; the colors appearing in bands with oblique lamination, giving the rocks a beautifully va- riegated appearance. 1,000 2,000 3,000 4,000 VERMILION CLIFF GROUP. No. 4, 50 feet. Red friable sandstone. No. 5, 180 feet. Massive sandstone ; cross-bedded ; with a few irregular beds of lime- stone not persistent horizontally; stained red on exposed surfaces. No. 0, 320 feet. Red sandstono ; thickly bedded. No. 7, 2 feet. Calciferous sandstone. No. 8, 100 feet. Orango or vermilion sandstone. No. 9, 5 feet. Light gray sandstones. No. 10, 400 feet. Orange sandstones ; rather massively bedded. SHINARUMP GROUP. No. 11, 800 feet. Bad laud sandstones, rapidly disintegrating ; argillaceous; weather ing iu variegated hills. No. 12, 80 feet. Conglomerate. No. 13. 195 feet. Red, bad-land sandstono ; very friable, with much gypsum. No. 14, 100 feet. Greenish gray bad-land sandstone, with much gypsum, and rapidly disintegrating. No. 15, 8 feet. Compact gray sandstone. No. 16, 3S0 feet. Red sandstones and arenaceous shales ; gypsum in seams and joints. No. 17, 250 feet. Red and brown sandstone ; rather thinly bedded, with many ripple marks. No. 18, 50 feet. Conglomerate with angular and rounded fragments of limestone in a matrix of calciferous sand. The sandstones of this grojjp are well seen in the vicinity of Flaming Gorge on the soi\th side of the Green River; again between Dry Lake and Vermilion Creek north of Po Canon, and in a narrow zone on the south side of the Uinta Mountains, and in many other places on the tributaries of the Green and Colorado Rivers; and everywhere the lithologic characteristics are more or less persistent. The cross-bedded sandstones usually form a conspicuous landmark. 54 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. VERMILION CLIFF GROUP. The wagon road from Toqueryille to Paria, a little town on the Paria River, soon after climbing' the Hurricane Ledge readies the foot of the Vermilion Cliffs, and continues at this geological horizon until it commences to descend into the valley of the Paria. For seventy-five miles the road lies under this great ledge, whose salient buttes, deep alcoves, terraced and buttressed walls, towering pinnacles, all brightly colored in orange, vermilion and purple, and dotted here and there with straggling cedars and nut pines, constitute a grand panorama to the passing traveler. Flaming Gorge on the Green River is cut through beds of this group and receives its name from the bright colors of vermilion sandstone ; Laby- rinth Canon is cut through vermilion sandstone ; Glen Canon for the greater part of its course also, and fine exposures are seen along the Colorado Chiquito. SHINARUMP GROUP. South of the Vermilion Cliffs a low ledge or escarpment is seen capped with conglomerate. This is the Shinarump Conglomerate. The variegated beds above and below the conglomerate are seen in many places on either flank of the Uinta Mountains, and from time to time this horizon is brought up by faults or flexures in all the stretch of country which intervenes between the Shinarump Cliffs and the Uinta Mountains. UPPER AUBREY GROUP. Mr. Gilbert, as geologist of the Wheeler expedition, described certain groups of limestones, sandstones and shales as the Aubrey Group. Previous to his publication I had in manuscript divided these beds into two groups and given them names ; but in carrying out my determination to use the names of groups which had been adopted by others so far as such names were available, I have decided to call the two groups into which I wish to divide the Aubrey beds of Mr. Gilbert, the Upper and Lower Aubrey Groups The beds of the Upper Aubrey are exposed for thousands of miles along the Grand Caiion of the Colorado and its lateral canons, everywhere LOCALITIES WHERE THE GROUPS CAN BE STUDIED. 55 forming- the summit of the walls of these gorges. They are also well exposed along Marble Canon ; and Cataract Canon at the junction of the Grand and Green furnishes another good section. Good sections are obtained at Horse- shoe Canon, the Canon of Loclore, Whirlpool Canon, and Split Mountain Canon in the Uinta Mountains. • Its junction with the Shinarump Group above, in all these places can be plainly seen, and in like manner its junction with the Lower Aubrey Group is apparent. To the southward in the Grand Canon country these beds are a series of cherty limestones. At the junction of the Grand and Green they are a series of sandstones with intercolated cherty limestones, with a homogeneous sandstone at the summit 150 feet in thickness. In the Uinta Mountains we have a homogeneous gray sand- stone which we call the Yampa Sandstone, from 1,000 to 1,200 feet in thick- ness, capped by a hed which is believed to -be the equivalent of the one mentioned as found at the summit of the series at the junction of the Grand and Green, and varies from 150 to 200 feet in thickness. On the south side of the Uinta Mountains it is an indurated, calciferous sandstone, but on the north side of the mountains it is a cherty limestone, and on both flanks of these mountains it is characterized by a species of bellerophon. Here we have called it the Bellerophon Limestone. LOWER AUBREY GROUP. The Lower Aubrey Group is seen underlying the Upper Aubrey at all the localities mentioned for that group. In the Grand Calion it is a conspicuous group, its relations to the Upper Aubrey and the Red Wall Groups being well marked. At the junction of the Grand and Green the lines of demarkation cannot be so closely drawn but they appear again very clearly in the Uinta Mountains. RED WALL GROUP. The Red Wall Group is the most conspicuous feature of the Grand Canon of the Colorado and its tributary gorges. It often stands in a vertical wall 2,000 feet high or more, and is everywhere carved into a series of grand amphitheaters, which I have elsewhere tried to describe. There are two well defined members in the Grand Cation country ; the upper one 5(3 SEDIMENTARY GROUPS OF TOE PLATEAU PEOVINCE. thousand feet is a massive, homogeneous, saccharoid limestone ; the lower one thousand feet is eomposed ehiefly of thin beds of indurated limestones of very irregular stratification surfaces. These beds are somewhat argilla- ceous. The group is not well exposed in Cataract Canon, as the river has not yet cut through the beds at that point, and some very curious displacements along the river serve to obscure the characteristics of the beds that are exposed. In the Uinta Mountains the two members seen in the Grand Canon are represented by two massive, indurated limestones, often con- taining chert and separated by arenaceous shales. TONTO GROUP. I have elsewhere called these the rust colored beds, but Mr. Gilbert has called them the Tonto Group, and I accept his name. These beds are seen to overlie unconformably the beds of the Grand Canon Group and of the Grand Canon Schists. They are seen well exposed along or near the bottom of the Grand Canon, where the river makes its double detour around the Kaibab Plateau, and again farther westward, where the river makes another detour around the Shi-wits Plateau. -A group of sandstones and arenaceous shales is found below the Red Wall horizon in Lodore and Whirlpool Gallons, where the Green River cuts through the Uinta Mountains. In the beds of this latter place I have discovered Carboniferous fossils, and suppose them to be of the same age as the Tonto Group ; yet, as Mr. Gilbert has considered the Tonto beds to be of Silurian Age, I have called the latter Lodore Group provisionally. From geological considerations, I am inclined to consider the Tonto Group as forming the base of the Carboniferous series. The supposed Cruziana and metamorphosed corals discovered by Mr. Gilbert are not deemed by me to furnish sufficient evidence of their greater age. Their geological rela- tions being apparently the same as the Lodore series, I am inclined to refer them to the same horizon ; the latter have been demonstrated to be Carboniferous. My opinion is strengthened by the fact that I find in the Grand Canon 10,000 feet of sandstones, shales and limestones, under- lying them unconformably, and hence separated by a long period of ero- sion, and at the base of this latter series I have found Silurian fossils. I Uinta Mountains. Fig. 10.— Comparative gectione of Carboniferous strata. Cataract Canon. Grand Canon. i{ » 1000 _ 2000 - MOO _ 4000 UINTA MOUNTAIN SECTION. 57 consider the Tonto, Red Wall, Lower Aubrey, and Upper Aubrey Groups to represent the Carboniferous time from base to summit In Figure 10 I give a Uinta Mountain, Cataract Canon, and Grand Canon section of these groups, side by side, for comparison. The Uinta Mountain and Cataract Canon Sections were made bv Mr. J. F. Steward. UINTA MOUNTAIN SECTION. By J. F. Steward. UPPER AUBREY GROUP. No. 1, 175 feet. Calciferous sandstone, containing Bdlerophon, con- chifers, &c. No. 2, 1,400 feet. Massive buff sandstone. LOWER AUBREY GROUP. No. 3, 90 feet- Limestone, mottled dark, drab, and buff; very hard; cup corals and Product us abundant. / f No. 4, 200 feet. Buff limestono^very fossiliferous : Spirifer, Athyris, &c, abundant. No. 5, 75 feet. Heavy beddecl, bluish-drab limestone; lower portion buff colored. This bed is filled with nodules 1 No. 13, 400 feet. Thinly bedded, bluish limestone, with intercalated, thinly bedded sandstones and elay shales below. The limestones are con- cretionary and brecciated, and have many cavities filled with calcspar. No. 14, 100 feet. Greenish, micaceous shales, with beds of gray and brown sandstone, containing iron concretions. tonto group! No. 15, 75 feet. Limestones; a good marble; often mottled; some- times containing concretions of chert, No. 16, 600 feet. Rust colored sandstones; thinly bedded; indurated; greenish above. No. 17, 100 feet. Brown sandstone. UINTA GROUP. The Uinta Mountains arc chiefly composed of Uinta Sandstone. The western end of this range where it abuts against the Wasatch Range, I have not carefully studied; but to theV^eastward the broad, massive range is a grand sandstone structure. Other groups are turned up on their flanks, and in Red Creek Canon a lower groupns seen. On the southeast margin of the range a line of peaks may be seen extending across the Canon of Lodore, composed of groups of Red Wall Limestone. In the many deej) canons and gulches by which the range is cleft, in the many amphitheaters that are found along the crest of the range, and in the mural faces of its lofty peaks, everywhere the sandstones are made bare to the eye of the geologist; but the best sections can be made along the canons. In a subsecpient chapter some of these sections will be given. GRAND CANON GROUP. This group is exposed in the great southern bends of the Grand Canon, where the Colorado River passes the end of the Kaibab Plateau. The best exposure can be seen about ten miles below the mouth of the Little Colo- rado. Many of the lateral streams coming in from the west and north cut through this group and afford fine exposures. The best one probably is in 02 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. Kwd-gTint Valley. Some of the members are again exposed at the bottom of the Grand Canon, where it passes the Shi-wits Plateau. Lower Silurian fossils have been found at the base of this group. RED CREEK GROUP. The Red Creek Quartzite, with its intercolated beds of hornblendic, micaceous and chloritic schists, is well seen in Red Creek Canon. Other ex- posures can be seen at the head of Willow Creek, a little stream that conies down from tlie O-wi-yu-kuts Plateau, and empties into the Green River midway in Brown's Park. GRAND CANDN SCHISTS. This group is revealed in the depths of the Grand Canon in all its great southern bends. EPOCHS SEPARATING THE GROUPS. BISHOP MOUNTAIN CONGLOMERATE. The Bishop Mountain Conglomerate is found at different places to lie unconformably upon every group of the table which is represented in the Uinta Mountains and adjacent country. Its plane of demarkation repre- sents a cessation of the movements of displacement in the region over which it is found, and that the same region was planed down to a base level of ero- sion, which base level was continued during the accumulation of these beds, for it is believed to be a subaerial conglomerate ; but should further evidence prove it to be a subaqueous accumulation the plane of separation would then represent an epoch of change from a period of erosion to a period of depo- sition. This point will be more fully discussed hereafter. brown's park group. This group in Brown's Park is seen to lie unconformably on the Uinta Sandstone, and all the other Paleozoic, Mesozoic and early Cenozoic groups; the plane of demarkation, therefore, represents an epoch of change from a dry land to a submerged condition. The area over which it was deposited within the region of my study is of small extent, but the beds are known EPOCHS SEPARATING THE GROUPS. 63 to continue farther eastward beyond the belt examined; and it may be found as examination is carried farther in that direction to be conformable with the next lower. BRIDGER GROUP. The plane of demarcation between this group and the next m order is not always well defined. The change from the green sands or bad-land rocks to the indurated sandstones and limestones of the Upper Green River is transitional; yet the epoch of change is important, for the Upper Green River attenuates both to the east and west, and in the latter direction it entirely disappears, so that the Bridger beds lie with an apparent conformity, but actual unconformity, on the beds of the Lower Green River. This is seen in the vicinity of Carter Station. UPPER GREEN RIVER GROUP These beds are interpolated between the Bridger and Lower Green River, as described above, only in a portion of the country where the latter two occur. The Tower Sandstone which forms the base of the Upper Green River Group is laid down unconformably on the Lower Green River, the unconformity being represented by gentle valleys of erosion ; and there seems to have been a period of erosion or dry land conditions separating the Tower Sandstone from the Plant Beds of the Upper Green River also, and during this dry land period the sands of the Tower Sand- stone were eroded by rains and drifted by winds. After the deposition of the sands, the bottom of this great Green River lake was left bare for a time and the sands drifted in dunes. LOWER GREEN RIVER GROUP. The Lower Green River beds represent a period when minutely lami- nated bituminous shales and more massive limestones were deposited, the limestones prevailing as you descend in the series. These beds are all fresh water and are separated from those below by an abrupt plane of stratification which marks a change in the character of the sediments. The lower beds are soft, friable, and highly colored bad-land sandstones. But this plane of separation means something more. The conditions which 04 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. prevailed during- the deposition of the lower sandstones abruptly changed, leaving a part of the ancient lake dry and a part submerged, and in this submerged area the limestones and shales were deposited. BITTER CREEK GROUP. The Bitter Creek beds are chiefly bad-land sandstones. The area of lacustrine deposition had its greatest expansion during this time. The plane of demarkation separating it from the next group in order is one of great importance. When the beds of the underlying group had been laid down, and before these beds were formed, that movement began which, carried on through Cenozoic time, has given us the great Uinta upheaval. There seems to have been a widely spread dry land condition separating them, for on the flanks of the mountains the lower Bitter Creek beds rest unconformably on the next group, and this unconformity is by erosion and also by angle of dip. This is seen in several places. But the move- ment in upheaval in the Uinta Mountains was oscillatory, and we often find the upper members of the Bitter Creek series overlapping the older members, and in extreme cases all of the groups of Mesozoic Age also. The unconformity between the two groups away from the mountains is simply represented by erosion. The hard, gray sandstone, which is the upper member of the Point of Rocks Group, is often seen to have been eroded into gentle or more abrupt valleys, and the shales of the Bitter Creek Group were carried into and rilled these valleys. These facts are exhibited in very many places on either flank of the Uinta Mountains, and on either flank of the Aspen Mountain fold, or that fold the axis of which is seen in the Salt Wells Basin ; yet there are many points where the conditions of recent erosion are such that the junc- tion of the two groups are -more or less masked, and where the uncon- formity is less apparent. But this epoch cf change has a more important significance. The group below I have classed with the Mesozoic, the group above with the Cenozoic, and the change was from marine to lacustrine conditions. But this change was not abrupt ; brackish water fossils are found in the lower group associated with marine forms, and with these a few species of / EPOCHS SEPARATING THE GROUPS. 05 geophila ; and brackish water fossils, in perhaps a very few instances of the same species with those below, are associated with fresh water fossils ; hence the change from marine to fresh water conditions seems not to have been abrupt. It will be noted that the epochs of change which separate the fresh water Cenozoic groups all represent a change in character of the sediments, and also represent more or less abrupt contraction of the expanse of fresh water. This was very great during the Bitter Creek period ; somewhat less during the Lower Green River ; somewhat less during the Upper ; perhaps about the same, but less in some directions and greater in others, during the Bridger ; and when we reach that point of time represented by the Brown's Park beds the area was quite small. Those beds to which the name Wasatch Group has been given, and which are found on the eastern slope of the Wasatch Mountains, and stretching out to the eastward until they run under Lower Green River beds, are the western extension of the Bitter Creek beds, and hence the name Wasatch Group should be dropped. The conglomerate at the bottom of what was called the Wasatch Group is represented by the con- glomerates of the Bitter Creek Group on both flanks of the Uinta Mount- ains. The beds called the Washiki Group are the upper part of the Bitter Creek series. I have been unable to carry any line of demarkation between these beds over such an extent of country as would warrant their separation Trom the Bitter Creek series, yet this may be done, and in such a case the name of Washiki Group should be retained. In the region near Washiki Station, where they were first seen by Dr. Hayden, they are exceedingly conspicuous by reason of their brilliant colors. Professor Cope, who saw them a little farther to the southwest, thus appropriately describes them: "Several miles to the south we reach another bench whose bluffy face rises four or five hundred feet in buttress-like masses, interrupted at regular intervals by narrow terraces. This line is distinguished by its brilliantly colored strata, extending in horizontal bands along the escarp- ment. They are brilliant cherry-red, white, true purple with a bloom- shade yellow and pea-green, forming one of the most beautiful displays I 5 P G 0(5 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. ever beheld. The lower portions are of bright red, which color predom- inates toward the west, where the bluffs descend to a lower elevation. I found on them the remains of a turtle (Emys cuthnetlius Cope), and some boring's of a worm in a hard layer. On top of these are clay and slate- rocks of a muddy-yellow color, with their various ledges rising to perhaps five hundred feet" {vide United States Geological and Geographical Survey of Colorado, page 437). These latter beds are Lower Green River limestones. In the same article, and immediately preceding this quotation, Pro- fessor Cope says : " At a short distance to the southward another line of white bluffs extends across the line of travel. This is not more elevated than the preceding one ; I only found remains of tortoises in it." On either flank of the Aspen Mountain fold this group of beds weath- ering white is seen, and I have several times at first confounded them with the Lower Green River, but the shales of these beds are carbonaceous, and often contain more or less lignitic coal ; those of the Lower Green River are bituminous and yield oil. The limestones of the former are an^rewi- tions of shells or shell-marls. 0 THE CRETACEOUS GROUPS. m Planes of demarkation in the Cretaceous groups are not easily drawn. The three great, massive sandstones of the Point of Rocks Group are in many places- broken into thinner beds, and then it becomes impossible, with our present knowledge at least, to say to which of these members particular beds may belong. The group below usually is very thinly bedded ; some- times, however, these beds are thicker and more indurated, and when this is the case and the Point of Rocks Group is broken up it is difficult to draw a line between the two groups. The same difficulty arises in separating the yellow arenaceous shales and the black argillaceous shales. Wherever the two groups are exposed side by side, above are seen thinly bedded sand- stones and shales and below are black, minutely laminated shales, but it is very rare indeed that an exact line can be drawn. In the southern portion of the province the Salt Wells beds are massive, and there the separation is more easily made. The black shales of the Sulphur Creek Group are EPOCHS SEPARATING THE GROUPS. G7 ■r everywhere seen to rest upon a somewhat massive sandstone which is under- laid by bad-land sandstones, shales, conglomerates, &c, with a somewhat massive indurated sandstone at the bottom. There seems to be a very decided change in the paleontology of these groups from base to summit, but the fossils, so far as now known, do not afford definite lines of demar- kation. The relation of these groups to those established by Professors Meek and Hayden on the Upper Missouri is not well determined. I have care- fully tried to use their system of grouping and have failed. A very different lithologic series is observed, as must be apparent from a comparison of the two sections. Most of the fossils are of different species, and the few that can be referred to the species of Professors Meek and Hayden in that region present contradictory evidence. Those fossils that may be referred to "No. 2" are found above fossils which may be referred to " Nos. 3 and 4," and as we are tracing these beds over broad areas, and from time to time collecting new fossils, the stratigraphic relations of which should be given with their description, it seemed necessary that some grouping should be adopted, and I have given the best I could under the circum- stances. Perhaps after the paleontology is more thoroughly studied the Upper Missouri groupings can be adopted here, but my present opinion is that all such attempts will prove futile. These opinions are based chiefly upon geological reasons, viz : All the evidence that has been published by Dr. Hayden and members -of his corps concerning the Park Province, and all my own observations in that region, lead me to the conclusion that a long chain of islands stretched in a northerly and southerly direction through that region of country, separating the Cretaceous sea of the Plateau Prov- ince from the Cretaceous sea of the Upper Missouri ; probably not forming a continuous wall between the waters of the two, but separating them in such a manner that very different physical conditions prevailed. It is mani- fest that the Cretaceous sea of the Plateau Province was fed chiefly with the sediments of the Basin Province, for all the Cretaceous sediments rap- idly attenuate fr7. The base of the Carboniferous series is not found in Cataract Canon, but in the Uinta Mountains these beds rest unconformably upon the Uinta Group. In the Grand Canon they rest unconformably upon the Grand Canon Group and also upon the crystalline schists; hence in both places the plane of demarkation is important, and represents long periods of erosion. 70 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE UINTA GROUP. The Uinta Sandstone rests unconformably upon the Red Creek Quartz- ite; ten thousand feet of its upper members are deposited unconformably against that metainorphic group. It is evident, also, that the metamorphism was anterior to the deposition of the Uinta Group, for the beds of the latter, especially near the junction, are chiefly made up of fragments of the former; hence the unconformity is very great. The period of erosion separating the sandstones from the Carboniferous beds above was sufficient to carry away at least 3,000 feet of the Uinta Sandstone in some places. How much more was carried away we cannot say. To my mind this suggests that the Uinta Sandstone may be considered Devonian — an opinion which I would yield upon the slightest paleontologic evidence to the contrary. GRAND CANON GROUP. The Grand Cafion Group rests uncomformably upon the crystalline schists. The evidence of this is complete, for the lower sandstones and conglomerates first filled the valleys and then buried the hills of schistic rocks, and these conglomerates at the base of the group are composed of materials derived from the metainorphic hills about ; and hence metamor- phism was antecedent to the deposition of the conglomerates. The plane of demarkation separating this group from the Tonto Group is very great. At least 10,000 feet of beds were flexed and eroded in such a manner as to leave but fragments in the synclinals. Then followed a period of erosion during which beds of extravasated material were poured over the fragments, and these igneous beds also were eroded into valleys prior to the deposition of the Tonto Group. Fossils have been found at the base of the Grand Canon series, but they are not well preserved and little can be made of them. Still, on geo- logical evidence, I am of the opinion that these beds should be considered Silurian. RED CREEK QUARTZITE AND GRAND CANON SCHISTS. These are believed to be Eozoic. ******* THIS GROUPING TENTATIVE. 71 The grouping which I have given above should be considered as merely tentative, and will probably need some modification hereafter ; it may possibly need radical changes ; it would be very unsafe with our present knowledge to assume otherwise ; I know that it will need some interpolation in the Cretaceous groups in the southern part of the province. I should have been pleased to have delayed its publication until the entire province had been more thoroughly surveyed, but circumstances render it necessary that I should do something more than make general statements of the methods and results of the work which I have been doing. Congress has appropriated money from year to year for the work on the representa- tion of a few leading scientific men of the country that the work was being done with reasonable skill and economy ; but only the few who had time and were willing to examine the work in manuscript at the office could understand what we were doing, and it seemed but reasonable that a demand should be made for the publication of some specific results. Hav- ing concluded to commence the publication before the province was com- pletely surveyed, it was absolutely necessary that some grouping of the geological formations should be used. The map must be colored to show the distribution of geological formations, and of course names must be given to the formations thus represented on the map, and a nomenclature is necessary for discussion ; hence the publication of the table. But I shall be willing to modify it to any extent as facts are collected which seem to demand such a change, whether such facts are the results of my own labors or those of others. Still I present the table with some degree of confidence. The groups of rocks have been traced over broad areas, and in the district, the geology of which I am to describe in this report, the grouping fully represents the state of my knowledge. On account of the discussions which liave arisen concerning the age of certain beds of lignitic coal, the plane of demarkation between the Cenozoic and Mesozoic may subject me to criti- cism ; but, geologically, the plane is important, as it represents a decided physical change, and it certainly harmonizes with the opinion of paleontolo- gists to a degree that is somewhat surprising. All of the plants described by Professor Lescmereux and collected by himself and others within this province have been referred by him to divisions in the Tertiary, and are 72 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE. found in strata above this physical break, and hence I agree with him in considering them Tertiary. In subdividing the Cenozoic or Tertiary, Professor Lesquereux has attempted to draw very fine lines, dividing these beds into Eocene and Mio- cene, and further subdividing each of these two groups into upper, middle, and lower. In doing this he has done violence to the stratigraphy, and sometimes his upper, middle, and lower cross each other; but, in a general way, his Miocene is higher than his Eocene. All of the fossils described by Mr. Meek which have been found above this physical break, he has referred unhesitatingly to Tertiary, and all of the fossils found below the physical break, he has referred, unhesitatingly with some, doubtfully with others, to the Cretaceous. There is a single excep- tion to this in Ostrea Wyomingensis, which is a new species; and I am sure no paleontologist would insist that a new species of ostrea could be used as conclusive evidence in deciding the age of a group of beds. That Mr. Meek did not discover the physical break is not strange, for he did not see it. When he made his exploration in this region he was in ill health, and trav- eled by rail from station to station, stopping at these places and examining the rocks only in the vicinity of the stations. His health would not permit him to make long excursions in the country on foot, and it was impossible for him to obtain horses. He passed the physical break above mentioned on a railroad car, and his sections at Hallville and Point of Rocks are not connected by several hundred feet, as he states, and as I have since verified by passing over the ground; and the physical break is found in the gap. In like manner, on the opposite side of the Aspen Mountain uplift, he passed it in the cars between Point of Rocks and Green River Stations. The conclusions reached from a study of the vertebrate paleontology by Professors Leidy, Marsh, and Cope entirely harmonize with this division of the Cenozoic and Mesozoic. There is a single exception to this; Pro- fessor Cope described a dinosaur found near Black Buttes Station as Creta- ceous. I have verified the determination of the stratigraphic horizon by examining the place and finding other dinosaur bones; but this horizon is above the physical break, and the evidence of the dinosaur seems to be con- tradicted by the evidence furnished by many other species described by Professor Cope from about the same horizon. DIFFEKENT SUCCESSION OF COALS. . 73 LIGNITIC COAL. An examination of the section will reveal the fact that lignitic coal is found abundant from the base of the Cretaceous through the recognized groups of that division, and in three of the groups of the Tertiary, giving a horizon of 11,500 feet. I know of no lignite bearing group in the Pla- teau Province which may be said to be richer in this product than others, and it would have led to confusion to characterize any group as the " Lig- nite beds." While lignitic coal is found in great abundance through a long succes- sion of formations or groups, it is rarely or never the case that any partic- ular bed is persistent over a great area. In the Point of Rocks Group I have at one place found eleven beds, varying from ten inches to four feet in thickness, and three miles away where the exposure was complete so that no mistake could be made except by careless observation I have found each one of these beds represented by carbonaceous shales ; and facts simi- lar to this have been noted in all the other groups. It is frequently the case that, in studying the same group at two places separated by a few miles, a ver}^ different succession of coals will be observed. It seems that they were formed in small, irregular basins, from time to time, beginning with the Lower Cretaceous and ending high up in the Cenozoic. Dr. C. A. White has prepared a catalogue of the species which, so far, have been collected in the Plateau Province, by myself and those assisting me in the work, and tabulated them in groups agreeing with the above scheme. He has also appended to each an additional list of fossils collected by others. The general correlation of the section to established successions elsewhere must at present rest on the evidence furnished by this catalogue. CHAPTER III. INVERTEBRATE PALEONTOLOGY OF THE PLA- TEAU PROVINCE, TOGETHER W1TII NOTICE OF A FEW SPECIES FltGM LOCALITIES BE- YOND ITS LIMITS IN COLORADO, By Charles A. White, M. D. Washington, D. C, February 1, 187G. Sir: I have the honor to present the following- preliminary report upon the paleontological collections made by parties under your direction during the years 18G8 to 1875, inclusive; more especially upon the invertebrate fossils. The collections are large and important, comprising, besides the inver- tebrate fossils noticed and described on following pages, vertebrate remains from strata of the Carboniferous, Jurassic, Cretaceous, and Tertiary periods; and plants from those of the Cretaceous and Tertiary periods. The plants, from strata of the last named period especially, are abundant and interest- ing, comprising as they do representatives of the classes Acrogens, Endo- gens, and Exogens, the latter being greatly in excess of the others. Among the vertebrate fossils are the remains of fishes (Selachians, Gan- oids, and Teliosts), reptiles, and mammals. Besides these, a small collection borrowed from Mr. W. Cleburn contains part of the skeleton of a Passerine bird which was discovered by him in the Lower Green River Group, near Green River Station, Wyoming Territory. Some of the other discoveries of vertebrate remains are also worthy of notice here, among which may be mentioned two or three species of teliost fishes at the base of the Creta- i A. ccous series of Wyoming and Utah, and fragments of the skeleton of a very GENERAL OBSERVATIONS. 75 large reptile in Jurassic strata of Northwestern Colorado. The collection of Mr. Cleburn also contains two or three species of insects. The study of the collections as a whole, reveals many interesting" facts bearing upon the physical conditions of the regions examined, during the deposition of the strata from which they have been collected, some of which are briefly discussed on following pages. Among the more important of these is the identification of the marine genera Oculina,Phorus, Dcntalium, Patella, Venus, Mesodesma, &c, from the Tertiary strata of Bijou Basin, forty miles east of Denver, Colorado. This indicates the extension of open-sea marine deposits much farther into the interior of the continent during the Tertiary period than has been previously known. Upon following pages I present a classified catalogue of all the inver- tebrate species, following which are descriptions of the new species. This catalogue enumerates two hundred and sixty-two species in all, forty-eight of which are new to science, and described herein for the first time. Very respectfully yours, C. A. WHITE. Professor J. W. Powell, Geologist in charge of the Second Division United States Geological and Geographical Survey of the Territories. GENERAL OBSERVATIONS. The fossils of the collections of which the following pages are occupied in large part by a classified and partially descriptive catalogue, have been obtained from strata of the Carboniferous, Triassic, Jurassic, Cretaceous, and Tertiary periods; very largely from the immediate vicinity of the Green and Colorado Rivers and from portions of Northern Utah and Southern Wyom- ing. The areas from which they have been collected are very small com- pared with that of the great Plateau Province, the study of the invertebrate paleontology of which the preparation of this report is only a beginning. It is, therefore, too early to draw final conclusions concerning the general lessons which full collections from that great region will be sure to teach us, or to deduce at present, any very satisfactory generalizations; but it may not be unprofitable to mention some of the facts, in their order, that 76 INVERTEBRATE PALEONTOLOGY. [white. have been observed while making the collections in the field and also dur- ing- their more critical investigation in the laboratory. Some of these facts have an interesting bearing upon the characteristics of the fossil faunae of the periods which the collections represent, the relation of those faunae to each other, and to both fossil and recent faunae of the whole Plateau Province as well as those of other regions. For the purpose of facilitating reference to the groups of strata which have furnished the fossils, the following table is introduced. The classifi- cation of the formations used in this report is, for the geological ages and periods, the same as that of Dana's Manual of Geolog}^ (1874,) and for the groups of strata of the Pleateau Province, that of Professor Powell in his section of the Uinta Mountain region. Table of the formations of the Uinta Mountain Region. Thickness iu feet. Groups. Periods. Ages. 1,800. Brown's Park Group 2,000. Bridger Group 500. Upper Green River Group . 800. Lower Green River Group. 3,000. Bitter Creek Group Tertiary > Cenozoic. 1,800. 1,800. 2,000. 500. 1,100. 1,100. 1,800. 1,000. 1,000. 2,000. 460. Point of Rocks Group . . Salt Wells Group Sulphur Creek Group . . Henry's Fork Group White Cliff Group. ... Vermilion Cliff Group Shinarump Group — . Upper Aubrey Group . Lower Aubrey Group Red Wall Group Lodore Group > Cretaceous 1,200. Flaming Gorge Group . . . . > Jurassic ► Mesozoic. Triassicf > Carboniferous . > Carboniferous. GENERAL OBSERVATIONS. 77 In the following brief review of the faunal characteristics of the dif- ferent groups represented in the collections it is well to consider how far any peculiarities they present, different from those which characterize their position in time, may have been occasioned by the then and there prevail- ing physical conditions under which the strata were accumulated. Some of those conditions were limited both in extent and duration, but others were of a more general and constant character. Almost all of the fossils of these collections are the remains of mollusks and other aquatic animals. It is a well-known fact that the character of the material composing the bottom upon which such animals live constitutes one of the most important elements in their habitat; that not only species, but even genera and families, are often separated from each other in the same waters by a difference in the character of the material composing the bottom. It is this gradually-accumulating bottom material that has constituted the strata from which we now obtain the fossil remains. The prevailing material of the strata which have furnished the greater part of the fossils of our collections, especially those of Mesozoic and Cenozoic ages, having an aggregate thickness of not far from three and a half miles, is sand. The bottom of the waters, salt, brackish, and fresh, of all the periods of both those ages, was almost constantly, either wholly or in very large part, composed of sand. Such a condition as this, continued for so long a time, necessarily pro- duced a marked effect upon the faunae of those periods, giving them different or modified characteristics as compared with those of the same periods respect- ively in other parts of the world. Again, the evidence afforded by both the vertebrate and invertebrate collections, and by those of the florae of all the periods named in the section on a previous. page, is in favor of the existence during that time of a warm-temperate and uniform climate. Furthermore, the labors of the field geologists have shown that there is a great degree of conformability of the strata of all the subordinate groups, from those of the Carboniferous to those of the Tertiary periods, inclusive ; or at least that the cases of un- conformability are few and of comparatively slight degree. So great a degree of uniformity in such important conditions as these having prevailed, it is not strange that the groups of strata of the different periods respect- 78 INVERTEBRATE PALEONTOLOGY. [white: ively are not in all cases clearly defined by fannal characteristics, even although they may be separated by sufficiently distinct physical characters by the field geologist. The periods are, as a rule, very clearly separated from each other by fannal characteristics, there being a partial exception in the case of those of the upper group of the Cretaceous period and the lower group of the Tertiary. But these facts will be noticed under appropriate heads on fol- lowing pages. Our investigations further show that certain faunal characteristics which have hitherto been relied upon to fix the geological age of strata of marine, brackish and fresh water origin, respectively, are not parallel. In other words, our collections contain types or forms of fresh and brackish water origin that have been regarded as peculiar to the Tertiary period, which were obtained from strata that underlie those containing such marine types as are universally regarded as peculiar to Mesozoic age; showing conclu- sively, that so-called Tertiary fresh and brackish water types and Cretaceous salt water types co-existed. The land shells also that have been obtained from strata herein classified as Cretaceous, are of Tertiary or even of still more recent type. These facts have made it especially difficult to fix the period of our terrestrial, and fresh and brackish water fossils with satisfactory precision, if they were new species and obtained from unique and isolated localities. A striking peculiarity of the strata of the Plateau Province, is the large proportion among them of fresh and brackish water deposits. So far as at present known, all the strata of Carboniferous age are of marine origin, the first unmistakably fresh water accumulations yet discovered in the Plateau Province being of Jurassic age. The only species obtained from these fresh water strata is a Unio, which is one of ordinary recent type; as is also another species of Unio and some Viviparine shells, described by Meek and Hayden, from the valley of the Upper Missouri River. These facts again illustrate the comparatively small value that can be placed upon fresh water invertebrate forms as indices of the passage of geological time. Most of the Mesozoic strata were evidently deposited in water that was salt by virtue of having been a part of, or in communication with, the open GENERAL OBSERVATIONS. 71) ocean; but it is not improbable that many of the brackish water accumula- tions, especially those of late Cretaceous and early Tertiary age, may have been made in land-locked waters which had their saline character continued from former times by the teachings of surface drainage, similar to that of Great Salt Lake, but in a far less proportionate degree. This idea is sug- gested by the fact that the final change to exclusively fresh water lacustrine deposits was so gradual that all the former brackish water species, among which no open-sea forms have been discovered, passed away without any perceptible physical change in the accumulating strata. LOWER SILURIAN AGE. The Lower Silurian age is represented in the collections only by a very few imperfect fossils from Kwagunt Valley, Grand Canon of the Colorado, Arizona, The Brachiopod genera Lingidella and Obolella are recognized with a good degree of certainty, and, distributed through the small masses of rock which contain them, there are apparently fragments of two or three other species. These specimens doubtless belong to the Primordial period, and possess much interest as regards the geological age of the rocks which underlie and overlie them. , UPPER SILURIAN AND DEVONIAN AGES. The present collections contain no fossils from strata of either Upper Silurian or Devonian age, but it is not improbable that rocks of these ages will yet be discovered in the Plateau Province. CARBONIFEROUS AGE. The collections contain fifty species from strata of Carboniferous age, much the greater part of which are from the Lower Aubrey Group. A few are from the Upper Aubrey, and a still less number from the Red Wall Group, while none are reported from the Lodore Group, A large proportion of all these fossils are specifically identical with well- known forms in the strata of the Carboniferous or Coalmeasure period in the States of the Upper Mississippi Valley; and all but two of them belong to such types as we might naturally expect to find in the equivalents of 80 INVERTEBRATE PALEONTOLOGY. [white. those strata. These two belong to the two genera respectively Archimedes and Amplcxus, the former of which, especially, has been regarded as an exclusively- Subcarboniferous genus; and yet they are found in the Lower Aubrey Group, nearly three thousand feet above the base of the Carbonifer- ous series, and also above, and mingled with, types that have not hitherto been found in strata so low as the Subcarboniferous Few or none of the fossils of the collections are of such a character as to suggest the Permian age of the strata from which they were obtained, not even those of the Upper Aubrey Group. I have elsewhere shown* that the prevalence of certain types which have been relied upon to prove the Permian age of the strata containing them may. be due to peculiar physical conditions,. and I therefore regard it as not improbable that the time of the Permian period may be represented in the Plateau Province by the Upper Aubrey Group, although the distinguishing types are want- ing there. In view also of the mixture which we find, of Carboniferous and Subcarboniferous types in the same strata, it seems probable that the time of the whole Carboniferous age, including its three periods, Subcarbonifer- ous, Carboniferous, and Permian, is collectively represented by the four groups recognized in the Plateau Province. It seems probable, therefore, that, although some localities in Nevada and Montana have furnished collections of almost exclusively Subcarbonifer- ous types, we shall not, as a rule, be able to define in this region, the three periods into which the age is divided in other parts of the world. It seems also probable that no divisions of the Carboniferous strata of the Plateau Province can be made that will represent geological periods, well defined upon paleontological grounds, either corresponding to those already estab- lished in other parts of the world, or differing from them. MES0ZOIC AGE. TRIASSIC PERIOD. Some small collections of fossils which possess peculiar interest were collected by Mr. E. E. Howell, in 1874, from the following localities in Utah: At Toquerville ; Virgin River, south of Toquerville ; near Workman's 'Geology of Iowa, 1870, vol. i, page 249. GENERAL OBSERVATIONS- 81 ranch, ten miles east of Toquerville, and also two miles west of Kanab. They were obtained from the lower portion of the Shinarnmp Group, the lowest group of Triassic strata in the Plateau Province. The specimens are all very imperfect, but the following genera have been recognized : Pentacrinus, Rhynclwnella, Camjjtonectes, and Myalina. Besides these there were fragments of other conchifers, the generic relations of which are not recognizable. The specimens of Pentacrinus consist only of joints of the column, like those of P. asteriscus Meek and Hayden, so common in the Jurassic strata of the same region, and, indeed, seem undistinguishable from those of that species. So far as can be determined, the fragments of Bfryn- cJioneUa may be those of the Jurassic, it. gnatliophora Meek, and those of Camptonectes may belong to any one of the several species known to exist in the Jurassic strata of the Plateau Province. In short, if the collections had been placed in my hands for determination, without any statement of their stratigraphical position, I should have referred them to the Jurassic period with no other doubts than those suggested by the imperfection of the specimens. If their stratigraphical position is correctly reported, which I know no reason to doubt, it seems certain that the strata containing them ought to be referred to the Jurassic rather than to the Triassic period. Before such an important conclusion as this is reached, however, it will be necessary to secure more perfect and complete collections. JURASSIC PERIOD. Twenty-seven species have been recognized among the Jurassic fossils of the collections, at least four of which are new. With the exception of two Echinoderms all the species are molluscan. Considerable interest attaches to the fact that a species of TJn'io has been obtained from strata of this period at Flaming Gorge, Utah, indicating the presence of fresh water at that point at one time during the period. The fact is also of still further interest as indicating that the fresh-water molluscan types which became so prevalent in the Tertiary period were introduced early in Mesozoic time if not before. CRETACEOUS PERIOD. A much larger number of species, all of which are molluscan, have been obtained from strata of the Cretaceous than from those of any one of Opo $2 INVERTEBRATE PALEONTOLOGY. [white. the other periods represented in the collections. The entire absence of all articulate and molluscoidean species from all the Cretaceous collections is quite remarkable. All four of the groups of strata are represented in the collections, those from the Henry's Fork Group containing the smallest num- ber of species. The groups as a rule appear to be separated by good paleontological as well as physical characteristics. Those of the Henry's Fork and Sulphur Creek Groups, however, are similar, and the dividing line between the Salt Wells and Point of Rocks Groups appears to be indistinct as regards generic and family types; but, with very few exceptions, the species have not been found to pass from one group to another. The exceptions thus far noticed are those of species that have a very wide geographical as well as an un- usually great vertical range. The Henry's Fork and Sulphur Creek Groups, so far as they have been examined, appear to have been wholly open-sea deposits, no genera of brackish water habitat, except Ostrea and Anomia, which are also open-sea' forms, having been discovered in any of the strata, The Sulphur Creek Group is also remarkable for containing nearly all the Cretaceous Cephalo- pods of the collections; the only exceptions being a specimen of Baculites ovatus Say, from the Salt Wells Group in the valley of Red Creek, Utah, and species of Scapldtes from the same group two miles northwestward from Salt Wells Station, Wyoming. The Salt Wells Group is not only remarkable for its paucity of Ceph- alopods, but also in consequence of the fact that from among its strata we obtain the first Cretaceous fresh- water forms. Even among the fossils of some of its more distinctively marine strata, Ave obtain such forms as are usually found in the brackish and fresh water Cretaceous and Tertiary de- posits of that region. The earliest of the fresh or brackish water Cretaceous deposits that have been discovered in the Plateau Province occurs among strata of this group near Coalville, Utah, a fortunate exposure of which afforded Mr. Meek, a few years ago, species of the genera Unio, Ci/rcna} Physa, Ncritina, &c, all having a remarkably modern aspect; but the strata which contained them are immediately overlaid by those which contain Inoccramus, Gryplica, Anclmra, and-other distinctively Mesozoic forms. GENERAL OBSERVATIONS. 83 The Point of Rocks Group is well represented in the collections by molluscan species, all of which are either Conchifers or Gasteropoda. Among them are a few land shells, many fresh-water species, and all but a few of the remainder belong- to genera of known brackish-water habitat, Further- more, some species of these remaining few genera have been found asso- ciated with brackish-water forms. It thus appears that the formerly pre- vailing marine conditions over the region that we now call the Plateau Province began to draw to a close early in the epoch represented by this group, and had well nigh ceased at its close. - A good illustration of this gradual change is presented by the strata of the Point of Rocks Group at Upper Kanab, Utah, where, toward the base of the series exposed, the fossils are mostly marine; above these a greater proportion of brackish-water forms are introduced ; still higher up fresh-water forms prevail, and the upper strata contain only fresh water and land shells; the deposition of all the strata having evidently been continuous and uninter- rupted. Among the more interesting observations that have been made in rela- tion to the fresh water and land shells of this epoch of the Cretaceous period, are those concerning the great differentiation of types that had thus early taken place. To so great a degree had this differentiation then attained that the species of Unio, Helix, Physa, &c, seem to have been as diversified and well developed as they are at the present time. Indeed the species of these genera are so closely like some of those now living that they need only the fresh condition of recent shells to remove all suspicion of their great antiquity from the mind of the casual observer. After the foregoing statements concerning the fauna! characteristics of the Point of Rocks Group, one might naturally inquire for the reasons that have led to its reference to the Cretaceous rather than to the Tertiary period. Laying aside all considerations suggested by the vertebrate and floral remains that have been collected from its strata, the reply may be briely stated thus: There is no physical break between this group and the Salt Wells Group bejow it. Its strata contain at least three species of Inoceramus, which genus has never been known in strata of later date than the Cretaceous period. Odontobasis, a species of which has been obtained from nenr the summit of the group, is regarded as a Cretaceous genus; and in view of the $4 INVERTEBRATE PALEONTOLOGY. [white. facts before stated, that land and fresh and brackish water mollusks are comparatively valueless as indices of the passage of geological time, the presence of no known forms in its strata forbid the reference of this group to the Cretaceous, period. CENOZOIC AGE. TERTIARY PERIOD. The collections of Tertiary fossils contain sixty species, exclusive of those that were obtained from localities beyond the limits of the Plateau Province. All of them are either brackish of fresh water species; the only truly marine forms of Tertiary age being those obtained at Bijou Basin, Colorado, which have already been noticed, and, as they are also described and catalogued on following pages, they will not be considered in the fol- lowing general remarks, which are intended to apply mainly to that portion of the Province which lies north of the Uinta Mountains. One-half of all these species were obtained from the Bitter Creek Group, the lowest group of the Tertiary series. This difference in the rel- ative abundance of species in the different groups is of course due primarily to the conditions under which the species lived, but evidently in large part also to the very much greater geographical extent, as well as greater thick- ness, of this group than of any of the others. "Among the primary condi- tions referred to, an obvious one was, the continuance of the brackish waters, so common in the last epoch of the Cretaceous period, into the first epoch of the Tertiary in some localities, although they seem to have given place to wholly fresh waters in other localities before the close of the Cre- taceous period. Collections have been made from these brackish-water Tertiary strata at Black Buttes, Point of Rocks, and Rock Spring, all in the valley of Bitter Creek, Wyoming, and where they reach a thickness of from five to seven hundred feet above the base of the Tertiary series. The species are clearly distinct from all others, either of this or any of the other Tertiary groups; but it is not to be denied that, although they are also all specifically distinct from any of the species found in the underlying Point of Rocks Group of the Cretaceous period, there is a prevalent similarity of type between the fossils of the two groups that is apparent upon merely casual inspection. GENERAL OBSERVATIONS. 85 No true or exclusively marine species have been discovered in these brackish-water Tertiary strata, and it is probable that the waters in which they were deposited were previously cut off from the open sea, but yet retaining to a great degree their former saltness. The genera thus far dis- covered are Ostrca, Anomia, Corbula, Corbicula (Leptesfkes), Cyrena (Velori- tinci), and Neritina, besides the more exclusively fresh- water genera Unio, Gouiobasis, Vivipwus, Tulotoma, and Leioplaxf The final change to a wholly fresh, from the brackish water condition, which was never to be resumed, was so gradual that no physical difference appears in the strata accumulated under both conditions ; but from and after that change a uniformity of molluscan type prevailed through all the subsequent epochs of the Tertiary period, as represented in the Plateau Province, that is really remarkable. It is especially so if, as Professor Powell has suggested from stratigraphical considerations, these Cenozoic groups represent the whole of what is generally known as the Tertiary period. Here and there, at different places in each of the Tertiary groups, except the Brown's Park group, which, because of its barrenness of fossils, is not included in this discussion, a few locally restricted species have been found, amounting to a considerable number in the aggregate. But prevail- ing at numerous horizons through all these groups after the brackish-water condition had ceased, and often in great profusion, are the three molluscan genera Unio, Viviparus, and Goniobasis, which are almost invariably imme- diately associated and almost as invariably without other faunal associates except occasionally a large discoid Planorbis. The Unios are of several species, which are defined by characters simi- lar to those upon which accepted recent species of the genus are established; but I have been unable to discriminate with entire satisfaction more than one species each of Goniobasis and Viviparus among these prevailing forms in the northern part of the Plateau Province, from the upper part of the Bitter Creek Group to the top of the Bridger Group, inclusive, with the pos- sible exception of Viviparus Wyomingensis Meek, from the Bridger Group. The Planorbis just mentioned I have usually referred to P. spectabilis Meek, but in the Bitter Creek Group, especially south of the Uinta Mountains, a variety occurs with fewer and broader volutions, in which respect it cor- 80 INVERTEBRATE PALEONTOLOGY. [wi.itk. responds with the description of P. Utahensis Meek. The Vivipams and Goniobasis I have, in the following catalogue, referred respectively to V. paludinceformis Hall sp. and G. tenera Hall sp. Goniobasis nodttl'ifera Meek (— Cerithium nodulosum Hall) and G. Carteri Conrad, are regarded as syno- nyms of G. tenera; and from among the thousands of examples that have been collected from the strata under discussion, it would be easy to make selections that, if found separately, would be taken to indicate an equal number of species, as different from those as they are from each other. Fortunately, however, the specimens in all cases are so abundant that other selections may be made showing full intermediate gradations between all the species that have been, and doubtless all that may yet be, proposed from among them. The character and extent of the variations of these species in their geographical distribution, vertical range, and local association will be dis- cussed in a future report. It is, therefore, sufficient now to suggest that these forms will present some of the best opportunities for the zoologico- historical study of certain species through a great lapse of geological time that paleontology has ever furnished. This remarkable uniformity of moUuscan types through all the groups, together with their almost exact identity with recent types of fresh-water mollusca, seems at first view to present an argument against the supposition that those Cenozoic deposits occupied the whole of Tertiary time, when con- sidered only in relation to the invertebrate remains ; but the slight value of fresh-water mollnscan forms in such generalizations has already been shown. If relied upon at all, their modern aspect would seem to indicate late Ter- tiary time only, while, on the other hand, the physical connection of the lowest group with the uppermost group of Cretaceous strata is such as to leave no doubt that the former represents the earliest epoch of Tertiary time. Besides this several of the species found in the brackish-water layers at the base of the Bitter Creek Group are closely related to species found in similar deposits in Slavonia and referred to the Eocene Tertiary by. Brusina.* (See "Fossile Binnen-Mollusken aus Dalmatien, Kroatien, und Slavonien von Spiridion Brusina, Agram, 1874.") * It is an interesting fact that these collections of Tertiary fresh water mollnsks in Slavonia possess many Unioue and Vivipariue forms that arc of living American, and not European types, while all the American fossil fresh water forms with which I am acquainted are of American recent types. GENERAL OBSERVATIONS. 87 By comparing the invertebrate fauna of those fresh water Tertiary deposits with the faunae of existing fresh waters we observe the entire absence from our collections of all articulates, except a species of Ci/pris and the insects discovered by Mr. Cleburn. The list of Molluscan genera found in those ancient lakes compares closely with those of the great existing American lakes, notwithstanding the fact that the floral remains of the former indicate a uniform and much milder climate than now exists in either of the two regions. Thus far no well defined fluvatile deposits have been discovered, but it is probable that those fresh water species found among brackish water forms constituted portions of the molluscan faunas of rivers that flowed into the ancient lakes or estuaries, because they are specifically different from, and more various than, those of the purely fresh water deposits. This sugges- tion is supported by the well-known fact that the molluscan types of lakes are fewer than those of rivers, while the differentiation is yet greater in brackish and greater still in marine waters. In closing these remarks upon the Tertiary period a question arises similar to the one briefly considered at the close of the remarks upon the Cretaceous period, namely : Why has the dividing line between the strata of the Tertiary and Cretaceous periods been drawn where it is rather than at some horizon either above or below it ? The answer is nearly the same as in the former case There is no physical break in the Cretaceous strata, from the base of the series to the top of the upper, or Point of Rocks Group, at which horizon there is at all observed points, extending over a large region, considerable unconforma- bility by erosion of the lower strata of the Bitter Creek Group, upon the upper strata of the Point of Rocks Group. The separation of the two periods, as represented by the strata of the Plateau Province, is a physical rather than a paleontologieal one. Upon purely paleontologieal ground it is difficult to indicate precisely where the line should be drawn, but it should evidently be somewhere near the one indicated in Professor Powell's section. This being the case, and it being necessary to draw such a line, it is more rational to draw it upon a line of a physical break than through conformable strata either above or below it. / £g INVERTEBRATE PALEONTOLOGY. [wiiitk. CATALOGUE OF THE FOSSILS COLLECTED BY THE VARIOUS PARTIES IN THE FIELD DURING THE YEARS 1868 TO 1875, INCLUSIVE. CARBONIFEROUS AGE. CARBONIFEROUS PERIOD. RED WALL GROUP. 1. Chaetetes milleporaceus Troost. — Gypsum Canon, Colorado River, Utah. The specimens have their characters obscured by silicification, but they doubtless belong to this species. It also occurs in the Lower Aubrey Group. (See No. 4.) 2. Syringopora multattenuata McChesney. — Gypsum Canon, Colorado River, Utah. 3. Campophyllimi f . — Cataract Canon, Utah. A large species, larger than C. torquium Owen, but the specimens are too imperfect for full specific description. LOWER AUBREY GROUP. 4. Chaetetes milleporaceus Troost, — Split Mountain Canon, Green River, Utah. Also obtained from the Red Wall Group. (See No. 1.) 5. Fiskdipora f . — Confluence of Grand and Green Rivers, Utah. Weathered specimens. 6. Syringopora f. — Confluence of Grand and Green Rivers, Utah. Specimens consisting of rather small, flattened, or subspherical masses. Tubes small and much distorted, but imperfect by silicification. 7. Amplexus zapJirenttformis White. — Near Echo Park and at Split Mountain Canon, Utah. Described on a following page. 8. Loplwphyllum proliferum McChesney. — Confluence of Grand and Green Rivers, Utah. Characters more nearly typical than those of the variety called Sauridens found near Santa Fd, New Mexico. - 9. Lithostrotion f — York, Utah ; west base of Wasatch range. 10. Acervularia 1. — Split Mountain Canon, Green River, Utah. CATALOGUE OF FOSSILS. 89 11. Arcliceocidaris cratis White. — Confluence of Grand and Green Rivers, Utah. Described on a following page. 12. Arcliceocidaris trudifer White. — Confluence of Grand and Green Rivers, Utah. Specimens consisting only of imperfect spines. 13. Erisocrinus typus Meek and Worthen. — Confluence of Grand and Green Rivers, Utah. The type specimens of Meek and Worthen were obtained from the Coal-measures of Illinois, and consisted only of calyces. Ours shows about two and a half centimeters in length of the arms, each of which consists of a double, interlocking series of pieces ; the arms when closed lying so closely together as to leave only a linear suture between them. 14. Scaphiocrinus caroonarius Meek and Worthen. — Confluence of Grand and Green Rivers, Utah. 1 5. Eupacliycrinus platybasis White. — Confluence of Grand and Green Rivers, Utah. Described on a following page. 16. Polypora f. — Confluence of Grand and Green Rivers, Utah. A large specimen, having unusually large fenestrates. Obverse side only shown. 17. Fenestella ?. — Near Echo Park, Utah. Obverse side only shown. 18. Archimedes f. — Near Echo Park, Utah. Specimens consist of two axes only, one of which is dextral and the other sinistral in its volu- tions. They are, however, both referred to one species. 1 9. Piscina f. — Bee-hive Point, near Horseshoe Canon, Utah. A single lower valve. 20. Productus punctatus Martin. — Confluence of Grand and Green Rivers, Utah. 21. Productus longispinus Sowerby ?. — Near Echo Park and at the con- fluence of Grand and Green Rivers, Utah. 22. Productus costatus Sowerby? — Near Echo Park, Utah. The speci- mens consist of the ordinary American forms generally referred to that species, but are probably distinct from it, 23. Productus costatus var. — Near Echo Park, Utah. Like No. 22 in 90 INVERTEBRATE PALEONTOLOGY, [white. • essential characters, except that the radiating costse are reduced in size to that of raised stride. 24. Produetus Prattenianus Norwood. — Confluence of Grand and Green Rivers, Utah. Some of the specimens possess the median row of spines or nodes upon the ventral valve, like those which Dr. Newberry named P. nodosus. 25. Produetus semireticulatus Martin. — Confluence of Grand and Green Rivers, Utah. All the examples are of the variety named P. Ivesii by Dr. Newberry. 26. Produetus Nebrascensis Owen. — Confluence" of Grand and Green Rivers, Utah. 27. Produetus muricatus Norwood and Pratten. — Near Echo Park, Utah. 28. Produetus midtistriatus Meek. — Confluence of Grand and Green Rivers, Utah. 29. Chonetes granulifera Owen. — Confluence of Grand and Green Rivers, Utah. 30. Chonetes platynota White. — Near Echo Park, Utah. 31. Hemipronites crinistria Phillips. — Near Echo Park and. at the con- fluence of Grand and Green Rivers, Utah. It also occurs in the Upper Aubrey Group. (See No. 49.) 32. Meekella striatocostata Cox. — Confluence of Grand and Green Rivers, Utah. 33. Spirigera subtilita Hall. — Confluence of Grand and Green Rivers, and near Echo Park, Utah. Occurs also in the Upper Aubrey Group. (See No. 50.) 34. Spirtfer cameratils Morton. — Confluence of Grand and Green Rivers, Utah. 35. Spirifer Rocky montanus Marcou. — Split Mountain Canon and near Echo Park, Utah. Occurs also in the Upper Aubrey Group. (See No. 51.) 36. Spiriferina Kentuckensis Shumard. — Confluence of Grand and Green Rivers, Utah. Occurs also in the Upper Aubrey Group at the same locality. (See No. 52.) 37. Aviculopecten occidentalis Shumard. — Two miles above Belleview, Utah. CATALOGUE OF FOSSILS. 91 38. Myalina -f. — Confluence of Grand and Green Rivers, Utah. The specimens have the aspect of M. recurvirostris Meek and Worthen, but all of them have lost their beaks. (See No. 53.) 39. AUorisma subcuneata Meek and Hay den? — Confluence of Grand and Green Rivers, Utah. The examples of the collection agree with those of this species from the typical localities, as given by Meek and Hayden, and they also agree very nearly with the description and figures given by Dr. Newberry of A. capax. 40. Edmondia Aspenwallensis Meek. — Confluence of Grand and Green Rivers, Utah. 41. Pleuroplionis f. — Confluence of#Grand and Green Rivers, Utah. The species is probably new, but the specimens are too imperfect for full description. 42. Schizodus Wheeleri Swallow. — Confluence of Grand and Green Rivers, Utah. 43. Betterophon f. — Confluence of Grand and Green River§, Utah. 44. Enomplialus 1. — Confluence of Grand and Green Rivers, Utah. The specimens are imperfect, but are probably those of E. luxus White. 45. Pleurotomaria excelsa Newberry. — Confluence of Grand and Green Rivers, Utah. 46. Natkopsis remex White. — Confluence of Grand and Green Rivers, Utah. Described on a following page. 47. PMUipsia f. — Near Echo Park, Utah. UPPER AUBREY GROUP. 48. Discina f. — Bee-hive Point, near Horseshoe Canon, Utah. 49. Hemipronites crinistria Phillips. — Bee-hive Point, near Horseshoe Canon, Utah. Occurs also in the Lower Aubrey Group. (See No. 31.) 50. Spirigera subtilita Hall. — Bee-hive Point, near Horseshoe Canon, Utah. Occurs also in the Lower Aubrey Group. (See No. 33.) 51. Spirtfer Rocky montanus Marcou. — Bee-hive Point, near Horseshoe Canon, Utah. Occurs also in the Lower Aubrey Group. (See No. 35.) 92 INVERTEBRATE PALEONTOLOGY. [white. 52. Spiriferina Kentuckcnsis Shumard. — Confluence of Grand and Green Rivers, Utah. Also occurs in the Lower Aubrey Group at the same locality. (See No. 36.) 53. Myalina P, — Confluence of Grand and Green Rivers, Utah. Occurs also in the Lower Aubrey Group at the same locality. (See No. 38.) 54. Edmondia f. — Confluence of Grand and Green Rivers, Utah. 55. Bdlcroplwn Montfortianus Norwood and Pratten. — Confluence of Grand and Green Rivers, Utah. The specimens are imperfect, but have apparently the marking's and other characteristics of this species as it occurs in the Coalmeasures of the Mississippi Valley, but the shell is evidently more elongate or less compact. • 56. BelleropJion carbonarius Cox, var. subpapillosus White. — Bee-hive Point, near Echo Canon and near Echo Park, Utah. Also at Junction Mountain and near Diamond Peak, Northwestern Colorado. This variety differs from the typical forms of the species in its larger size and in having tl^at part of the last volution, which is plain in the typical shell, marked with distant, slightly-raised papillae, arranged in rows corresponding to and continuous with the revolving striae. MESOZOIC AGE. JURASSIC PERIOD. FLAMING GORGE GROUP. 57. Pentacrinus asteriscus Meek and Hay den. — Flaming Gorge ; Santa Clara River, two miles below Gunlock ; Diamond Valley ; Lower Potato Valley; "White Hills," south of Twelve-mile Creek, near Gunnison; three or four miles south of Kanara, Utah ; and at the Vermilion Hog-backs, Northwestern Colorado. The specimens consist only of joints of the col- umn, the only part of the species yet discovered. 58. Spine of Echinoid, too indefinite for either specific or generic rec- ognition. Santa Clara River, two miles below Gunlock, Utah. 59. Rliy/iclwnella gnatlwpliora Meek. — Flaming Gorge, Utah, and Ver- milion Hog-backs, Northwestern Colorado. CATALOGUE OF FOSSILS. 93 60. Bhynchonclla Myrina Whitfield. — Vermilion Hog-backs, Northwest- ern Colorado. 61. Ostrea strigileada White. — Island Park and Flaming Gorge, Utah; and Vermilion Hog-backs, Northwestern Colorado. 62. Ostrea (Alectryonia) procimibens White. — Vermilion Hog-backs, Northwestern Colorado. Shell of moderate size, irregularly ovate in mar- ginal outline ; margins coarsely dentate ; valves moderately thick, usually attached by nearly the whole surface of the lower one. 63. Camptonectes stygius White. — Lower end of Long Valley ; mouth of Thistle Creek, Spanish Fork Canon ; Upper Kanab ; and three or four miles south of Kanara, Utah. 64. Camptonectes bettistriatus Meek and Hayden. — Three or four miles south of Kanara, Utah. 65. Camptonectes platessiformis White. — North base of Aquarius Pla- teau, Southern Utah. Resembles C. platessa White in its surface-markings, and C. Stygius White in its marginal outline. 66. Gervillia 1. — North base of Aquarius Plateau, Southern Utah. Resembles G. Montanaensis Meek, but the axis of the shell is more oblique to the hinge-line, and the wing narrower than in that species. 67. Pinna f.— Mouth of Thistle Creek, Spanish Fork Canon, Utah. Surface radiately ribbed both above and below the median angle; probably a new species, but the specimens are too imperfect for satisfactory description. 68. Modiola subinibricata Meek. — Vermilion Hog-backs, Northwestern Colorado. # 69. Myophoria f. — Island Park, Utah. 70. Trigonia Americana Meek. — Flaming Gorge, Utah. 71. Trigonia Montanaensis Meek. — North base of Aquarius Plateau, Utah. 72. Trigonia Conradi Meek and Hayden. — Flaming Gorge, Utah. 73. Trigonia f. — Santa Clara River, two miles below Gunlock, Utah. 74. Unio Steivardi WTiite. — Flaming Gorge, Utah. Described on a fol- lowing page. 94 INVERTEBRATE PALEONTOLOGY. [white. 75. Trigonella f. — Island Park, Utah. Shells rather small-exte- rior nearly perfect, but the hinge is unknown, and they are referred to this genus provisionally. 70. Undetermined Conchifers. — Two species. Flaming Gorge; north base of Aquarius Plateau; Square-top Butte, east base of Aquarius Plateau, Utah. 77. Undetermined Conchifer. — -Different from No. 76. Island Park, Utah. 78. Myacites f. — South base of Thousand-lake Mountain, Utah. 79. Neritina f.— "White Hills", south of Twelve-mile Creek, near Gunnison, Utah; and Vermilion Hog-backs, Northwestern Colorado. 80. Neritina ft Powelli White.— Mouth of Thistle Creek, Spanish Fork Canon, Utah. Described on a following page. 81. Undetermined Gasteropods. — Two species, very small, and the speci- mens numerous. Mouth of Thistle Creek, Spanish Fork Canon, Utah. 82. BeleMnitcs densus Meek and Hayden. — Island Park and Flaming Gorge, Utah; and Vermilion Hog-backs, Northwestern Colorado. 83. Ammonites cordiformis Meek and Ha}^den. — A small fragment of the inner volutions. Vermilion Hog-backs, Northwestern Colorado. CRETACEOUS PERIOD. henry's fork group. 84. Ostrea prudentia White. — Head of Water-pocket Canon, Southern Utah. 85. Gryphca Piteheri Morton. — Near Twin Mesas; Upper Pine Creek; near Last Chance Creek; head of Water-pocket Canon and Lower Potato Valley, Southern Utah. The specimens are numerous, and show the usual extreme variations. It occurs also in the Sulphur Creek Group. (See No. 97.) 86. Exof/yra Icevinscula Eoemer. — Lower Potato Valley and south base of Mount Hillers, Southern Utah. It occurs also in the Sulphur Creek Group. (See No. 98). 87. Exogyra ponderosa Roemer. — Head of Water-pocket Canon, South- ern Utah. It occurs also in the Sulphur Creek Group, in Utah, and was obtained from a locality in Middle Park, Colorado. (See Nos. 99 and 202.) CATALOGUE OF FOSSILS. 95 88. Plicatula liydrotlieca White. — Head of Water-pocket Canon, South- ern Utah. Described on a following page. 89. Inoceramus Hoivelli White. — Lower Potato Valley and Upper Pine Creek, Utah. Described on a following page. 90. Avicula linguiformis Shumard. — Lower Potato Valley and Sink Spring, Utah. 91. Camptonectes platessa White. — Head of Water-pocket Canon, South- ern Utah. 92. Undetermined Conchifers. — Lower Potato Valley, Utah. 93. Cardium f. — Head of Water-pocket Canon, Southern Utah. A rather large subspinous species, probably new, but the specimens are all imperfect. 94. Callista Dciveyi Meek and Hayden. — Head of Water-pocket Canon, Southern Utah. The specimens consist only of casts in sandstone. 95. Area f. — Head of Water-pocket Canon, Southern Utah. An elongate species, represented only by a cast in sandstone. SULPHUR CREEK GROUP. 96. Ostrea congesta Conrad. — Fold, ten miles west of Black Bluff, Green River, and Island Park, Utah; base of Diamond Peak and near Vermilion Canon, Northwestern Colorado. The specimens from the last-named locality are unusually large, and a few of them were found free, but most of them were, as usual, found attached to fragments of Inoceramus deformis. The species occurs also in the Point of Rocks Group, Utah, in Western Kansas, and in Middle Park, Colorado. (See Nos. 159 and 200.) 97. Gryphea PitcJteri Morton. — Near Black Bluff, on Green River; Upper Kanab; fold, ten miles west of Black Bluff and Sink Spring, Utah. It also occurs in the Henry's Fork Group. (See No. 85.) 98. Exogyra Icevhiscula Roemer. — Upper Kanab, and near Black Bluff, on Green River, Utah. Occurs also in Henry's Fork Group, Utah. (See No. 86.) 99. Exogyra ponderosa Roemer. — Upper Kanab, Utah. It occurs also in Henry's Fork Group, Utah, and in Middle Park, Colorado. (See Nos. 87 and 202.) 9() INVERTEBRATE PALEONTOLOGY. [whitk. 100. Inoceramns deformis Meek. — Fold ten miles west of Black Bluff on Green River, and Island Park, Utah. Base of Diamond Peak and near Vermilion Canon, Northwestern Colorado. It accurs also at the base of the Point of Rocks Group, near Coalville, Utah; in western Kansas, and in Mid- dle Park, Colorado. (See Nos. 167 and 203.) 101. Lucina siibundata Hall and Meek. — Upper Kanab and Thistle Creek, Utah. A species probably identical with this occurs in the Salt Wells Group at Coalville, Utah. (See No. 132.) 102. Leiopistha Mechii White.— Upper Kanab and Sink Spring-, Utah. 103. Turnus sphcnoideus White.— Upper Kanab, Utah. Described on a following- page. 104. Lunatia concinna Hall and Meek.— Sink Spring", Utah. 105. Anclmra ruida White.— Upper Kanab, Utah, Described on a fol- lowing page. 106. Anchura prolabiata White,— Upper Kanab and Sink Spring, Utah. Described on a following page. 107. TarriteUa Uvasana Conrad. — Upper Kanab, Utah. 108. Cassiope Whitfiddi White.- — Upper Kanab, Utah, 109. Pseadobuccinum Nebrascense Meek and Hay den.— Upper Kanab, Utah. 110. Baculites ovatus Say. — Fold ten miles west of Black Bluffs, Green River, Sink Spring, near Twin Mesas, and Upper Kanab, Utah. Occurs also in the Salt Wells Group. (See No. 157.) ' 111. Scaphites Warreni Meek and Hay den.— Fold ten miles west of Black Bluff, Green River, Utah. 112. Ammonites Woolgari Mantellt— Last Chance Creek, Utah. 113. Ammonites f. — -Fold ten miles west of Black Bluff, Green River, Utah. This species is of the type of A. Woolgari, but the volutions are proportionally deeper and the umbilicus smaller than in that species. 114. Ammonites — f, — Upper Kanab, Utah, Specimens imperfect, but they indicate a species quite different from any others in the collections. 115. Bnchiceras Sivcdlovi Shumard.= — Upper Kanab, Utah, 116. Helicoceras f. — Near Twin Mesas, Utah. The specimens show two rows of long dorsal spines and a crenulated or transversely undu- CATALOGUE OF FOSSILS. 97 la ted surface. They are so compressed in shale that the character of the coil is not shown, and may, therefore, probably belong to the genus Crioceras. 117. Helicoccras f. — Upper Kanab, Utah. A fragment, different from No. 116. 118. Belemnitella f. — Upper Kanab, Utah, and Sulphur Creek, Bear Eiver City, Wyoming. The specimens are more or less imperfect, but they closely resemble, and are probably identical with, B. mucronata, so common in the Cretaceous strata of New Jersey. 119. Serpula intrica White. — Upper Kanab, Utah. SALT WELLS GROUP. 120. Ostrea solemscus Meek. — Coalville, Lower Salina Canon, and near False Creek, Utah; Bear River City, and Hilliard Station, Wyoming. 121. Ostrea (Alectryonia) sannionis White. Weber Valley, near Coal- ville, Utah. Described on a following- page. 122. Ostrea {Alectryonia 1. — Near False Creek, Southern Utah. The specimens are fragmentary, but they indicate an unusually large species of this subgenus. 123. Gryphea f. — Coalville, Utah. The specimens are imperfect, but they seem to indicate a species materially different from G. Pitclieri Morton. ^-^124. Anomia ?>. — Coalville, Utah. 125. Inoceramus probkmaticus Schlotheim. — Lower Salina Canon and Coalville, Utah; Bear River City, Wyoming. 126. Inoceramus ?. — Two miles northwestward from Salt Wells Station, Wyoming. 127. Inoceramus Gilberti White. — Near Last Chance Creek, Southern Utah. Described on a following page. 128. Avicula (Pseudoptera) rhytopliora Meek. — Coalville, Utah. 129. Modiola (Brachydontes) multilinigera Meek. — Coalville, Utah. 130. Area Coalvillensis White. — Coalville, Utah. Described on a fol- lowing page. 131. Macrodon - f. — Coalville, Utah. A rather large, elongate species, represented only by a sandstone cast. 7 P G 98 INVERTEBRATE PALEONTOLOGY. [white. 132. Lucina subundata Hall and Meek! — Coalville, Utah. Apparently identical with that species. (See No. 101.) ^133. Cardium curium Meek and Hayden. — Coalville, Utah. 134. Cardium subcurtum Meek. — Coalville, Utah. ^135. Cyrena (Veloritina) securis Meek. — Coalville, Utah. Mr. Meek's types were from the Salt Wells Group, Sulphur Creek, Bear River City, Wyoming, hut ours, although imperfect, seem to belong to the same species. 136. Gyrena (Veloritina) erecta White. — Upper Kanab, Utah, and Bil- liard Station, Wyoming. Described on a following page. -137. Tellina (Arcopagia) Utahensis Meek. — Coalville, Utah. ' 138. Tellina modesta Meek. — Coalville, Utah. 139. Mactra cirenaria Meek. — Coalville, Utah. 140. Corbida nematophora Meek. — Coalville, Utah. 141. Corbida ?.— Coalville, Utah. 142. Martesia ?.— Coalville, Utah. 143. Physa f. — Coalville, Utah. One imperfect example only was found. It was associated with shells of marine type only, but it never- theless seems to possess the characters of a true Physa. 144. Neritina Bannisteri Meek. — Hilliard Station, Wyoming. The type specimens of this species were obtained by Mr. Meek from among brackish and fresh water forms near Coalville, Utah. No fresh, or exclusively brack- ish water forms were found associated with our examples, although the geo- logical horizon is doubtless identical, or very nearly so, at the two localities. 145. Neritina pisum Meek — Coalville, Utah. 146. Neritina (Velatella) pcdelliformis Meek. — Coalville, Utah. 147. Lunatia Utahensis White. — Coalville, Utah. Described on a fol- lowing page. " 148. Ancliura fusiformis Meek. — Coalville, Utah, and Sulphur Creek, Bear River City, Utah. 149. TurriteUa micronema Meek. — Coalville, Utah. 150. TurriteUa Coalvillensis Meek. — Coalville, and ten miles southeast of Sahara, west of Cone Mountain, Utah. 151. JEidimcUa funicida Meek. — Coalville, Utah. CATALOGUE OF FOSSILS. 99 152. Turbonilla (Chemnitzia) Coalvillensis Meek. — Coalville, Utah, and Hilliard Station, Wyoming-. 153. Gyrodes depressa Meek. — Coalville, Utah. 154. Fusus (Neptunea) Gabbi Meek. — Coalville, Utah. 155. Fusus (Neptunea) Utahensis Meek. — Coalville, Utah. 156. Admetopsis gregaria Meek. — Coalville, Utah. \bl.mBaculites ovatus Say. — Below "Wall Rock," basin of Red Creek, Utah. Occurs most commonly in the Sulphur Creek Group. (See No. 110.) 158. ScapJiites >f. — Two miles northwestward from Salt Wells Station, Wyoming-. POINT OF ROCKS GROUP. 159. Ostrea congesta Conrad. — Near the base of the group, Coalville, Utah. The species occurs most abundantly in the Sulphur Creek Group of the Plateau Province ; but it has a wide geographical, as well as a great stratigraphical, range. (See Nos. 96 and 200.) 160. Ostrea t. — Upper Kanab, Utah. 161. Ostrea f. — Bear River Vallev, near Mellis Station, where it is associated with fresh and brackish water mollusks. 162. Ostrea Coalvillensis Meek. — Coalville, Utah. 163. Ostrea insecura White. — Two miles west of Point of Rocks, Wyo- ming. Described on a following page. 164. Anomia grypliorhynchus Meek. — Two miles west of Point of Rocks, Wyoming. 165. Inoceramus f. — Top of Aspen Mountain, but near the base of the group, Wyoming. The species is nearly like I. sagensis Owen, but the specimens are too imperfect for specific identification. 166. Inoceramus f. — Upper Kanab, Utah. It has the general aspect of both I. Howelli and I. fragiUs, but differs from both in essential details. 167. Inoceramus deformis Meek. — Near the base of the group, Coalville, Utah. This species is most common in the Sulphur Creek Group, but it has a wide geographical, as well as a great vertical, range. (See Nos. 100 and 203.) 100 INVERTEBRATE PALEONTOLOGY. [white. 168. Unio gonionotus White. — Sevier Cliffs, twelve miles above Pan- guitch, Utah. Described on a following page. 169. Unio — . ?. — Associated with the last (168), but differs from it in its more convex beaks and in wanting the plications of that species. 170. Unio bettiplicatus Meek. — Bear River Valley, near Mellis Station, Wyoming. 171. Unio Vetustus Meek. — Bear River Valley, near Mellis. Station, Wyoming, and Canon of Desolation, Utah. 172. Cyrena (Veloritina) Diirkeei Meek. — Bear River Valley, near Mellis Station, Wyoming. 173. Cyrena (Veloritina) ?. — Upper Kanab, Utah. 174. Cyrena (Veloritina) cytlierifprmis Meek and Hayden. — Two miles west of Point of Rocks, Wyoming. 175. Corbula undifera Meek. — Rock Spring, Wyoming. 176. Corbula piriformis Meek. — Bear River Valley, near Mellis Station, Wyoming. 177. Corbula tropidopliora Meek. — Two miles west of Point of Rocks, Wyoming. 178. Limncea f. — Upper Kanab, Utah. 179. Limncea 1. — Bear River Valley, near Mellis Station, Wyo- ming. 180. Planorbis (Batliyomplialus) Kanabensis White. — Upper Kanab, Utah. Described on a following page. 181. Pliysa Kanabensis White. — Upper Kanab, Utah. Described on a following page. 1 82. Pliysa f. — Bear River Valley, near Mellis Station, Wyo- ming. 183. Physa f. — Upper Kanab, Utah. Associated with No. 181, but it is a larger species, and has a much shorter spire, the volutions of which are more broadly shouldered on the proximal side of the suture. 184. Rhytophorus priscus Meek. — Bear River Valley, near Mellis Sta- tion, Wyoming. 1'85. Rhytophorus Meekii White. — Bear River Valley, near Mellis Sta- tion, Wyoming. Described on a following page. CATALOGUE OF FOSSILS. 101 18G. Helix f. — Cafion of Desolation, Utah. 187. Helix Kanabensis White. — Upper Kanab, Utah. Described on a following page. 188. Goniobasis nitidula Meek. — Bear River Valley, near Mellis Station, Wyoming. 189. Goniobasis insculpta Meek. — Rock Spring, Wyoming. 190. Goniobasis chrysalis Meek. — Bear River Valley, near Mellis Sta- tion, Wyoming. 191. Goniobasis Nebrascensis Meek and Hayden. — Canon of Desolation, Utah. . ' 192. Goniobasis clirysaloidea White. — Bear River Valley, near Mellis Station, Wyoming. Described on a following page. 193. Goniobasis Cleburni White. — Bear River Valley, near Mellis Sta- tion, Wyoming. Described on a following page. 194. Goniobasis f. — Upper Kanab, Utah. — It is associated with Pyrgidifera Jmmerosa Meek, and bears some resemblance to G. Cleburni, but it has a proportionally much shorter spire. The specimens are all sand- stone casts. 195. Pyrgulifera Jmmerosa Meek. — Bear River Valley, near Mellis Sta- tion, Wyoming, and Upper Kanab, Utah. 196. Viviparus PanguitcJiensis White.— Sevier Cliffs, twelve miles above Panguitch, and Upper Kanab, Utah. 197. Campeloma macrospira Meek. — Bear River Valley, near Mellis Station, Wyoming, and Canon of Desolation, Utah. 198. Odontobasis buccinoidea White. — Two miles west of Point of Rocks, Wyoming. Described on a following page. 199. Turritella f. — Upper Kanab, Utah. Near the base of the group. CRETACEOUS FOSSILS FROM BEYOND THE LIMITS OF THE PLATEAU PROVINCE. 200. Ostrea congesta Conrad. — Western Kansas, and near Platte Canon, Middle Park, Colorado. 201. Ostrea ■ ?.— Near Platte Canon, Middle Park, Colorado. A large biconvex species. 102 INVERTEBRATE PALEONTOLOGY. [white. 202. Ezogyfa ponderosa Roenier. — Near Platte Canon, Middle Park, Colorado. 203. Inoceramus deformis Meek. — Western Kansas. 204. Inoceramus ( Volviccramus) exogyroides Meek. Three miles north- eastward from Hot Springs, Middle Park, Colorado. 205. Inoceramus Barabini Morton?. — The specimens vary from the typical forms in being deeper from hinge-line to base. 206. Avicula ParJcensis White. — South of Grand River, Middle Park, Colorado. Described on a following page. 207. Heteroceras f. — Three miles northwestward from Hot Springs, Middle Park, Colorado. The species is represented by a fragment only. CENOZOIC AGE. TERTIARY PERIOD. BITTER CREEK GROUP. 208. Ostrea Wyomingensis Meek. — Point of Rocks, Black Buttes, and Rock Spring, Wyoming. 209. Ostrea arcuatilis Meek. — Black Buttes, Wyoming. 210. Anomia — f. — Black Buttes, Wyoming. 211. Unio proplieticus White. — Black Buttes, Wyoming. Described on a following page. 212. Unio petrinus White. — Black Buttes, Wyoming. Described on a following page. 213. Unio f. — Black Buttes, Wyoming. A large massive species, but much shorter than U petrinus, with which it is associated. 214. Unio f. — Near Evanston, Wyoming. A large, elongate species, but the specimens are too imperfect for specific recognition or de- scription. 215. Unio Leanus Meek'?. — South Fork of Vermilion River, near Dia- mond Peak, Northwestern Colorado. 216. Unio bracliyopisthus^N\\\tQ. — Black Buttes, Wyoming. Described on a following page. 217. Corbicula {Leptestltes) fracta Meek. — Black Buttes, Wyoming. CATALOGUE OF FOSSILS. 103 218. Cyrena (Veloritina) Bannister i Meek. — Point of Rocks, Wyoming. 219. Pisidiwn saginatwn White. — Almy Coal Mines, near Evanston, Wyoming-. Described on a following page. 220. Corbula subundata White. — Point of Rocks, Wyoming. Described on a following page. 221. Corbula crassitelliformis Meek. — Black Bnttes, Wyoming. 222. Planorbis Utahensis Meek. — South base of Pine Valley Mountains, Utah. (See No. 245, and also general remarks on page 85.) 223. Planorhis f. — Almy Coal Mines, near Evanston, Wyoming. 224. Planorbis (Bathyomphalus) f. — Almy Coal Mines, near Evanston, Wyoming. The specimens consist of fragments only, but they indicate a large, well marked species of this subgenus. 225. Physa pleromatis White — Southeast flank of Quien Hornet Mount- ain, Wyoming ; east base of Pine Valley Mountains, Utah, and many other localities. 226. Physa f. — Almy Coal Mines, near Evanston, Wyoming. 227. Helix ?. — Almy Coal Mines, near Evanston, Wyoming. 228. Helix ?.— Different from No. 227. East base of Pine Valley Mountains, Utah. 229. Helix peripheria White. — South base of Pine Valley Mountains, Utah. Described on a following page. 230. Neritina volvilineata White. — Black Buttes, Wyoming. Described on a following page. 231. Goniobasis tenera Hall sp. — Various localities. (See Nos.' 247, 259, and 265, and also general remarks on page 85.) 232. Goniobasis f . — Almy Coal Mines, near Evanston, Wyoming. This species is related to G. Nebrascensis Meek and Hayden, but is more elongate. 233. Goniobasis Wyomingcnsis Meek. — Black Buttes, Wyoming. 234. Hydrobia recto White. — Almy Coal Mines, near Evanston, Wyoming. Described on a following page. 235. Hydrobia Utahensis White. — West base of Mu-si-ni-a Plateau, 1,000 feet below its summit, Utah. 104 INVERTEBRATE PALEONTOLOGY. [white. 236. Viviparus plicappressus White. — Black Buttes, Wyoming". De- scribed on a following1 page. 237. Viviparus trochiformis Meek. — West base of Mn-si-ni-a Plateau, tain, 1,000 feet below its summit, 238. Viviparus trochiformis var. — Associated with No. 337. 239. Viviparus paludincBformis Hall sp. — Various localities. (See Nos. 248, 260, and 266, and also general remarks on page 85.) 240. Tulotoma Thompsoni White. — Black Buttes, Wyoming. Described on a following page. 241. Leioplaxf turricula White. — Black Buttes, Wyoming. Described on a folloAving page. LOWER GREEN RIVER GROUP. 242. JJnio Shoshonensis White. — West side of Snake River, six miles north of Junction Mountain ; cliffs four miles northwestward from the head of Vermilion Canon and Dry Mountains, Northwestern Colorado. Described on a following page. It occurs also in the Upper Green River Group. (See No. 249.) 243. Unio f . — Two miles east of Lawrence Station, Wyoming. Base of the group. 244. Sphccrium 1. — Four miles northeastward from the head of Vermilion Canon, Northwestern Colorado. 245. Planorbis Utahensis Meek. — West side of Snake River, six miles north of Junction Mountain, Northwestern Colorado. It occurs also in the Bitter Creek Group. (See No. 222, and also general remarks on page 85.) 246. Helix riparia White. — Eight miles below Green River Station, Wyoming. Described on' a following page. 247. Goniobasis tenera Hall sp. — Various localities. (See Nos. 231, 259, and 265, and also general remarks on page 85.) 248. Viviparus paludinceformis Hall sp. — Various localities. (See Nos. 239, 260, and 266, and also general remarks on page 85.) UPPER GREEN RIVER GROUP. 249. Unio Shoshonensis White. — Henry's Fork and Alkali stage-sta- CATALOGUE OF FOSSILS. 105 tion, Wyoming. Described on a following page. It occurs also in the Lower Green River Group. (See No. 242.) 250. Unio f. — Henry's Fork, Wyoming. 251. Splicerium f. — Alkali stage-station, twenty-one miles north- ward from Green River Station, Wyoming. 252. Planorhis spectabiUs Meek. — Henry's Fork, Wyoming. Occurs also in the Bridger Group. (See No. 263, and also general remarks on page 85.) 253. Planorbis — — f . — Henry's Fork, Wyoming. A small species, marked with fine revolving1 lines. 254. Pliysa f. — Henry's Fork, Wyoming. 255. Succinea papillispira White. — Alkali stage-station, Wyoming. De- scribed on a following j)age. 256. Helix f. — Henry's Fork, Wyoming. A small species, somewhat resembling the recent H. perspectives. 257. Pupa incolata White. — Henry's Fork, Wyoming. Described on a following page. 258. Pupa arenula White. — Henry's Fork, Wyoming. Described on a following page. 259. Goniobasis tenera Hall sp. — Various localities. (See Nos. 231, 247, and 265, and also general remarks on page 85.) 260. Viviparus paludinaformis Hall sp. — Henry's Fork and Alkali stage- station, Wyoming, and various other localities. At the first-named locality the specimens are below the usual average size. (See Nos. 239, 248, and 266, and also general remarks on page 85.) 261. Cypris f. — Henry's Fork, Wyoming. This species seems to be specifically different from C. Leidyi Evans and Shumard. BRIDGER GROUP. 262. Unio Haydeni Meek. — Near Fort Bridger, Wyoming. 263. Planorhis spectabiUs Meek. — Henry's Fork, east of Fort Bridger, and six miles west of Badland Mountains, Wyoming. Occurs also in the Upper Green River Group. (See No. 252, and also general remarks on page 85.) 106 INVERTEBRATE PALEONTOLOGY. [white. 264. Flujm- Bridgerensis Meek. — Henry's Fork, east of Fort Bridger, Wyoming. 265. Goniobasis tenera Hall sp. — Various localities. (See Nos. 231, 247, and 259, and also general remarks on page 85.) 266. Viviparus paludincB for mis Hall sp. — Various localities. (See Nos. 235), 248, and 260, and also general remarks on page 85.) 267. Viviparus Wyomingensis Meek. — Near Fort Bridger, and six miles west of the Cameo Mountains, Wyoming. This seems to be specifically dis- tinct from the prevailing form that I have referred to V. paludinceformis, being a larger, thinner, and more inflated shell. brown's pakk group. 268. Physa f. — This is the only invertebrate species discovered in the strata of this group, and all the examples of it are too imperfect to .serve as the basis of a specific description. TERTIARY FOSSILS FROM BEYOND THE LIMITS OF THE PLATEAU PROVINCE. 269. Flustra f. — Bijou Basin, forty miles east of Denver, Colo- rado. The specimens are found incrusting the oyster, No. 270. 270. Ostrea f. — Bijou Basin, forty miles east of Denver, Colo- rado. The species is a very large one ; the largest example is nearly a foot in length and proportionally broad. 271. Cyrena ( Veloritina) f. — Fresh-water Tertiary deposits, Crow Creek, Colorado, where it was found associated with No. 278. 272. Corbicula Poivelli White. — Bijou Basin, forty miles east of Denver, Colorado. Described on a following page. 273. Venus 1. — Bijou Basin, forty miles east of Denver, Colo- rado. The specimens are fragmentary, but the hinge is shown. 274. Petricola ?. — Burrows only. Bijou Basin, Colorado. 275. Mesodesma Bishopi White. — Bijou Basin, forty miles east of Den- ver, Colorado. Described on a following page. 276. Dentalium f. — Bijou Basin, Colorado. A small longitudi- nally striated species. DESCRIPTIONS OF NEW SPECIES. 107 277. Dentalium f. — Bijou Basin, Colorado. Much like No. 276, except that its surface is marked only by encircling lines of growth. 278. Melania Larunda White. — Crow Creek, Colorado, where it is associated with No. 271. Described on a following page. 279. Patella ?. — Bijou Basin, Colorado. A single small exam- ple. 280. PJiorus exonerates White. — Bijou Basin, Colorado, forty miles east of Denver, Colorado. Described on a following page. 281. Cerithhim f. — Bijou Basin, Colorado. A single, small, imperfect example. DESCRIPTIONS OF NEW SPECIES OF INVERTEBRATE FOS- SILS FROM STRATA OF THE CARBONIFEROUS, JURASSIC, CRETACEOUS, AND TERTIARY PERIODS. CARBONIFEROUS PERIOD. R a d i at a. Actinozoa. Genus AMPLEXUS Sowerby. Amplexus zaphrentiformis (sp. nov.). — Corallum having the external aspect of Zaphrentis rather than of Amplexus, being elongate-conical in form, more or less curved and tapering to a point or small pedicil at the base; epitheca well developed, having its surface marked by the usual concentric wrinkles and lines of growth, and with longitudinal lines marking the position of the septa, the latter not being very distinct; calyx circular or subcircular, the plain portion of the surface at its bottom equal to one-third or more of the diameter of the corallum; septal fossette well developed, situated at the con- cave side of the corallum; septa thirty or forty in number, rather strong; transverse plates numerous, well developed, somewhat irregular, and ending exteriorly against a moderately well developed external wall, which is dis- tinct from the epitheca proper. This external wall contains no vesicles and apparently consists of solid coralline substance. 108 INVERTEBRATE PALEONTOLOGY. [white. The largest example in the collection is nearly nine centimeters in length, the calyx having a diameter of twenty-five millimeters; but the average size of nearly one hundred examples is considerably less. This species differs from all other species of Amplexus known to me in its zaphrentoid form, but its plain calyx-bottom, its broad transverse plates, and the absence of a vesicular zone, leave no doubt as to the propriety of referring it to the genus Amplexus. Position and locality. — Lower Aubrey Group; Split -Mountain Canon, and near Echo Park, Utah. Echinodermata. Genus EUPACHYCRINUS Meek and Worthen. JEnpachycrinus platybasis (sp. nov.). — Calyx nearly flat; basal pieces small, concealed by the first joint of the column, which is proportionally large; subradial pieces rather small or of medium size, their inner ends also covere'd by the first joint of the column; judging from the portion of them that is visible, they are all of nearly regular rhombic outline; first radials niuch broader than long, broadly convex from side to side and abruptly convex from within, outward, all of them ending with a regular obtuse angle between the subradial pieces except the left anterior one, the angle of which is made a little irregular by the interposition of the second anal plate ; first anal piece of the same size and shape as the subradial pieces; second anal piece apparently nearly as large as the first, between which and the left anterior first radial piece it is interposed, reaching nearly as far inward as the first radial piece does, and at which point it ends with an acute angle; plates all massive. Remainder of the structure unknown. Sutures all linear; surface nearly or quite smooth. Diameter 'of the calyx, eighteen millimeters. This species differs from the typical forms of the genus in the extreme flatness of its calyx, but the arrangement, number, and general character of the pieces composing it leave no doubt as to the propriety of referring it to JEitpacliycrinus. Position and locality. — Lower Aubrey Group; confluence of Grand and Green Rivers, Utah. DESCRIPTIONS OF NEW SPECIES. 109 Genus ARCH^EOCIDARIS McCoy. Arch ceocid aris cratis (sp. nov.). — Spines slender, gradually tapering from base to point; shaft ornamented with sharp, distant spinules, each about one and a half millimeters long and pointing strongly upward; basal ring promi- nent, plain, except the fine crenulation of its edges, and situated very near the proximal end of the spine. Surface apparently smooth. Length about six centimeters; diameter just above the basal ring nearly three millimeters; diameter of basal ring about four millimeters. The collections of the Geological Survey of Nebraska in the cabinet of the Smithsonian Institution contain a single spine of this species, which, together with that of these collections, is all that is known of the species. It may be readily recognized by its smooth, slender shaft, with its distant, sharp spinules. Position and locality. — Lower Aubrey Group; confluence of the Grand and Green Rivers, Utah. Mollusca. Gasteropoda. Genus NATICOPSIS McCoy. Naticopsis remex (sp. nov.). — Shell of ordinary size, very oblique when adult, by the elongation and enlargement of the last volution ; volutions about four, convex, increasing rapidly in size, the last one large and much produced ; spire small and short ; suture impressed. Surface marked by the usual lines of growth, and, although that of the specimens in the collec- tion is not very well preserved, there are some indications of the presence of faint revolving striae also. Length across the longest diameter of the aperture and body volution of an average-sized specimen, twenty-three millimeters ; short diameter of the same, seventeen millimeters. Position and locality. — Summit of the Lower Aubrey Group ; confluence of the Grand and Green Rivers, Utah. HO INVERTEBRATE PALEONTOLOGY. [white. JURASSIC PERIOD. Mollusca. Conchifera. Genus UNIO Retzius. Unio Stewardi (sp. nov.). — From the Jurassic strata at Flaming- Gorge of Green River, near the northern boundary line of Utah, some portions of a moderately large Unio were obtained that belong to an undescribed species. The valves are broadly oval in marginal outline, broadly but somewhat uniformly convex; beaks very near the anterior end; lest massive ; surface apparently marked only by the ordinary lines and imbri- cations of growth ; cardinal and lateral teeth both strong ; the lower lateral tooth of the left valve, and also that part of the hinge of the right valve against which it shuts, both strong and rounded into the cavity of each valve respectively, and both end posteriorly by abruptly rounded ends. Length of largest example, eight and a half centimeters ; height, sixty- two millimeters. Compared with U. nucalis Meek and Hayden, the only other species of the genus known to me from American Jurassic strata, it is larger, more massive, the beaks placed more anteriorly, and the cardinal and lateral teeth more massive. Specific name given in honor of Mr. J. F. Steward, of Piano, 111., its discoverer. Gasteropoda. Genus NERITINA Lamarck. Neritini ? ? Powelli (sp. nov.). — Shell moderately large, obliquely sub- ovate in outline ; volution;; about three or three and a half, rapidly increas- ing in size, the last one much expanded ; spire depressed, the apex scarcely appearing by side view of the shell ; suture slightly impressed ; aperture large, broadly subcircular or subtetrahedral ; a broad rounded revolving prominence extends around the volutions, nearer to their distal than prox- imal side, and another less prominent one between the first one and the suture ; the first one, especially, gives a degree of angularity to the last volution and to the margin of the aperture. DESCRIPTIONS OF NEW SPECIES. HI Surface marked by ordinary lines of growth, and also by somewhat prominent folds parallel with them ; the folds being stronger upon the revolving prominences before mentioned than elsewhere, and disappear upon the under surface of the shell. Greatest diameter of the largest example, twenty-eight millimeters; breadth of the same, twenty millimeters ; height, the aperture resting upon the table, fifteen millimeters. By carefully digging out the stony filling I have been unable to find any trace of a thickened inner lip such as characterizes the Neritidse, but the body seems to be small, simple, and without even a proper columella. The shell has the external aspect of a member of the family Neritidse, but it is not without much hesitation that I refer it to the genus Neritina. Indeed, this reference of it is made only provisionally until further investi- gation can be made. This disposition of it is made partly because it seems properly referable to no other established genus, and partly in view of the facts published by Brinkhorst in his Monog. Gast. et Ceph. de la Crate Sup. du Limbourg, 18G1. In that work lie describes and figures two species, Nerita rugosa Hoeninghaus, and N. parvula Brink., which he shows to have been so fossilized that the callus which formed the thickened inner lip was entirely removed by a natural process of solution, leaving the remainder of the shell intact, and in a condition similar to that of the species here described as regards the absence of an inner lip, but natural casts of his species showed that they originally possessed a well developed one. No such casts have been found with our shells, and it is not improbable that they were originally without any thickened inner lip. If so, our shell cannot be properly referred to any genus with whicjj I am acquainted, and in case further investigation shall leave no doubt that the shells have not been changed from their original character, I propose for it the generic name of Lyosoma. Specific name given in honor of Prof. J. W. Powell, geologist in charge of the Second Division United States Geological and Geographical Survey. Position and locality. —Flaming Gorge Group; mouth of Thistle Creek, Spanish Fork Canon, Utah. 112 INVERTEBRATE PALEONTOLOGY. [white. CRETACEOUS PERIOD. Mollusca. Conchifera. Genus OSTREA Linnaeus. Subgenus Alectryonia Fischer. Ostrea (Alectryonia) sannionis (sp. nov.). — Shell rather small, alate at both sides of the beak, irregularly subquadrate in marginal outline, its longitudinal axis curved, the convexity of the curve being forward, almost as wide across the alations as at the base, but constricted in the middle ; beaks small, not prominent, directed slightly backward ; lower valve mod- erately convex ; scar of attachment at the beak small or absent ; ligament- area short, rather broad ; its longitudinal furrow shallow but well defined, transversely striated, and pointing obliquely backward; posterior alation narrower than the anterior one, and a little longer than the corresponding alation of the other valve ; muscular scar comparatively large, situated nearly mid-length of the valve and near the posterior margin, curved- spatulate in outline, the broadest end being toward the base of the shell ; upper valve nearly flat, but in other respects corresponding with the lower. Surface of both valves marked by the ordinary lines and lamellations of growth common to the genus and by numerous crenulated radiating pli- cations, four or five of which upon each valve reach the base of the shell, giving that margin a coarsely zigzag or toothed condition. The other pli- cations are smaller and die out at the sides of the shell and upon the alations. Length from base to beak of a large example thirty-eight millimeters; breadth near the front the same; across the wings, thirty-three millimeters. This is one of the most distinctly defined species of the genus known to me, and numerous examples of it show that it was subject to compara- tively little variation. Position and locality. — Near top of Salt Wells Group; Weber Valley, near Coalville; Utah. Ostrea insecura (sp. nov.). — Shell rather small, thin, elongate-suboval in outline when adult, snboval or snbcircular when young ; beaks and area DESCRIPTIONS OF NEW SPECIES. J13 small; scar of attachment usually small and sometimes absent; surface com- paratively smooth for an oyster; a few faint radiating plications appearing upon some examples. Length of largest example nearly five and a half centimeters ; breadth twenty-nine millimeters. Position and locality. — Point of Rocks Group; two miles west of Point of Rocks, Wyoming. Genus PLICATULA Lamarck. Plicatula hydrotJieca (sp. nov.). — Shell of ordinary size, irregularly sub- ovate in marginal outline; beaks rather narrow ; lower valve broadly con- vex ; hinge teeth well developed ; upper valve nearly flat, or slightly concave near the beak. Surface of both valves marked by small, slightly raised radiating plications, which are crenulated, a little irregular and more or less distinct upon all parts of the surface of both valves. Length, three centimeters ; greatest breath, twenty-four millimeters. Position and locality. — Henry's Fork Group; head of Water-pocket Canon, Southern Utah. Genus INOCERAMUS Sowerby. Inoceramus Gilberti (sp. nov.). — Shell irregularly suboval in marginal outline, the transverse diameter being greater than the vertical; front flat- tened; valves nearly or quite equal, both being gibbous and sometimes quite ventricose; umbones broad and elevated; beaks very near the front, incurved but not projecting beyond the front margin ; front nearly straight vertically, and forming nearly a right angle with the hinge; front margin rounded below to the basal margin, which is broadly convex for more than half the length of the shell; postero-basal margin extending obliquely upward, with a slight emargination to the posterior extremity, which is abruptly rounded to meet the downward-sloping postero-clorsal margin; dorsal margin straight, its length equaling more than half the long diameter of the shell. Upon each valve there is an obscure radiating shallow furrow or de- pression extending from the umbonal region to the postero-basal border and ending at the emargination there, before mentioned. >p G 114 INVERTEBRATE PALEONTOLOGY. [wi.itk. Surface marked by the usual lines of growth, and also by numerous extravagant and irregular concentric folds or wrinkles. This species belongs to the section of the genus that Brongniart has designated under the name of CatiUus. It is a peculiarly well-marked species and easily distinguished from all others found in the rocks of the great Rocky Mountain region. Transverse length of an average-sized specimen seven and a half centi- meters; height from base to hinge, five centimeters. Specific name given in honor of its discoverer, Mr. G. K. Gilbert, geologist of one of the survey- ing parties. Position and locality. — Salt Wells Group; near Last Chance Creek, Southern Utah. Inoceramus Hoivelli (sp. nov.). — Shell of medium size, obliquely and irregularly suboval in marginal outline, the vertical diameter being greater than the transverse; both valves having considerable convexity, that of the left valve greater than the other; beaks narrowed, prominent, the prominence of the left one greater than the other, both of them elevated above the hinge line, and also curving forward beyond the front of the shell; front flattened, extending almost straight downward from the front end of the hinge, with which it forms nearly a right, or slightly obtuse, angle. Antero- basal margin abruptly rounded to the base; basal margin short; postero- basal margin extending obliquely upward to the posterior extremity, straight- ened or slightly emarginate; posterior extremity abruptly rounded to meet the almost straight postero-dorsal margin. Between the axis of the body of the shell and the postero-dorsal margin there is* upon each valve a rather broad, shallow, but more or less distinct furrow or depression, extending from the umbonal region to the postero- basal margin, and ending at the emargination before mentioned. There is also a distinct alation upon each valve, separated from the body portion by a tolerably well-defined auricular furrow. Surface marked by the ordinary lines of growth, and also by moder- ately distinct concentric folds, but the surface has a rather smoother aspect than is usual with species of this genus. Height of an average-sized example, DESCRIPTIONS OF NEW SPECIES. 115 from base to beaks, seven and a half centimeters; greatest breadth, which is near the base, five centimeters; length of hinge, thirty-seven millimeters. This shell somewhat resembles I. frag'dls Hall and Meek, but differs from it in possessing the shallow radiating furrow upon the body of the valve, and also in having a distinct posterior ear, separated from the body of the valve by an auricular furrow. It also resembles an example of /. striatus Mantell, in the cabinet of the Smithsonian Institution, from Saxony, but the beaks of our species are more elevated and turned more forward than they are in that species. I. striatus is also without the shallow radiat- ing furrow before mentioned. It differs from I. flaccidus White in its smaller size, its smoother surface and more gibbous valves, that species being coarsely and extravagantly wrinkled. Specific name given in honor of Mr. II E. Howell, who discovered it while geologist of one of the surveying parties. Position and locality. — Henry's Fork Group; Lower Potato Valley and Upper Pine Creek, Utah. Genus AVICULA Klein. Avicula Parkensis (sp. nov.). — Shell small, slightly inequivalve, very oblique, elongate, thin at all the margins except the cardinal; anterior wing of ordinary size and shape; posterior wing rather large and long; both valves broadly but regularly convex; body of the shell broadest behind the middle; antero-basal border broadly convex; posterior extremity regularly rounded; postero-dorsal border nearly straight from the posterior border to the base of the posterior wing; beaks of ordinary prominence; surface ap- parently smooth. Length from the end of the anterior wing to the posterior extremity of the shell, thirty-four millimeters ; breadth across the widest part of the body, fifteen millimeters. This species resembles A. Ungidifera Shumard, but differs from that species in its more elongate form and more oblique hinge line. Position and locality. — Cretaceous strata; south of Grand River, Middle Park, Colorado. Genus ARCA Linnaeus. Arcaf Coalvillensis (sp.nov.). — Shell longer than high, moderately thick; test somewhat massive; beaks depressed, situated near the anterior end; 11(3 INVERTEBRATE PALEONTOLOGY. [white. umbones broad; anterior end rounded or subtruncate; base nearly straight or very broadly convex, and often slightly emarginate about the middle; posterobasal border rounded upward to the posterior extremity, which is abruptly rounded to the downward sloping, nearly straight postero-dorsal border, the latter forming an obtuse angle with the hinge border; hinge equal in height to about two-thirds the entire length of the shell. A slight depression or flattening extends from the umbo of each valve to its base, causing the straightening or slight emargination of the basal border before mentioned. Area nearly obsolete; hinge rather slender; two or three long, slender transverse teeth occupy its middle portion; seven or eight teeth cross the surface of its posterior end obliquely downward and inward, and about an equal number of smaller ones cross the anterior end almost vertically; the inner ones of the latter set of teeth being very small and situated nearly beneath the beaks. Surface marked by ordinary lines of growth, and by fine radiating lines, which are often obscure. Length, five centimeters; height, thirty- three millimeters. Position and locality. — Salt Wells Group; Coalville, Utah Genus UNIO Retzius. TJnio gonionotus (sp. nov.). — Shell elongate-subelliptical in marginal out- line; flattened' and thin when, young, but becoming gibbous or almost cylin- drical with age; dorsal margin broadly convex; base nearly straight; front regularly rounded; the rounding of the posterior end somewhat irregular, in consequence of the plications of the valves at that part; beaks obsolete, the umbonal region of each valve so flattened that they form an acute angle at the dorsum in the young, the angle increasing with age, so that it is very obtuse in the adult shell. Surface of the anterior portion of the shell marked by only the ordi- nary lines and lamellations of growth, but the posterior portion, comprising more than half the length, is marked by strong, more or less irregularly radiating plications, which begin faintly a little forward of the middle, and increase gradually in strength to the posterior and postero-basal margins, and increase in number by a few bifurcations toward those margins; curv- DESCEIPTIQNS OF NEW SPECIES. 117 nig- upward and backward from the uppermost of the longer plications there are several smaller, short ones that end at the postero-dorsal margin. Length of the largest example in the collection, sixty-three millimeters ; height, thirty-five millimeters. Young examples have very different propor- tions, as well as a marginal outline of different shape. This species differs conspicuously from any other fossil Unio known to me, although young examples of it have some resemblance to those of the recent species TJ. midti/plicatus, but the adult specimens have a very different aspect, It differs from TJ. oelliplicatus Meek, from equivalent strata in South- western Wyoming, in its general shape and in the position and distribution of the plications, they being most conspicuous on the anterior portion of that shell, while the corresponding portion of ours is plain. Position and locality. — Point of Rocks Group; Upper Kanab, Utah. Genus CYRENA Lamarck. Subgenus Veloeitina Meek. Cyrena (Vcloritina) erecta (sp. nov.). — Shell of medium size, subovate in marginal outline when adult, but subcircular when young, gibbous, espe- cially the upper median portion, but somewhat compressed laterally at the postero- basal portion; front and basal margins regularly and continuously rounded; postero-basal extremity somewhat abruptly rounded upward to the sloping, broadly rounded postero-dorsal margin; umbones elevated; beaks small, incurved, and pointing forward; postero-dorsal margin of each valve flexed strongly inward, so that the hinge-ligament is hidden from sight by side view of the shell. Surface marked by the ordinary lines of growth. Length, thirty millimeters; height from base to umbones, thirty-four millimeters. Position and locality. — Salt Wells Group; Upper Kanab, Utah, and Bil- liard Station, Wyoming. Genus TURNUS Gabb. Turwus sphenoidcus (sp. nov.). — Shell elongate-cuneate, inflated in front, narrowed, and laterally flattened behind; beaks anterior, incurved, adjacent; 118 INVERTEBRATE PALEONTOLOGY. [white. postero- dorsal margin sloping from behind the beaks to the posterior ex- tremity, and apparently capped by a slender, accessory plate; posterior extremity abruptly rounded; basal margin nearly straight; front regularly rounded, both laterally and vertically; anterior gape consisting of a narrow, vertical slit that occupies the middle of a somewhat prominent projection at the antero-basal portion of the shell, which projection has the shape of a Norman shield, as seen by front view, when both valves are in their natural position; umbonal groove distinct and moderately deep, causing a distinct groove upon the stony internal casts of the shell, which is of about the same dimensions and character as that which is left by the radiating internal rib; besides these two grooves, there is another, somewhat broader furrow radiating from behind the beak of each valve to near the posterior end. A broad, cake-like accessory plate covers the beaks and the space between them; and, apparently, two others, one upon each valve, occupy the space between the umbonal plates and the top of the Norman shield-shaped pro- jection before mentioned. Surface marked by fine, concentric, raised lines, besides the radiating furrows before mentioned. The masses of rock from which our specimens were broken out, contained what appear to have been calcareous, siphonal tubes, but none of them were found to be unmistakablv connected with the shells. Length, thirteen millimeters; greatest height, seven millimeters ; breadth at the front, six millimeters. Position and locality. — Sulphur Creek Group; Upper Kanab, Utah. Gasteropoda. Genus RHYTOPHORUS Meek. Bliytopliorus Meekii (sp. nov.). — Shell subfusiform; spire moderately pro- duced, nearly one-third as long as the entire length of the shell ; volutions about six, convex, the last one somewhat large, elongate, convex, and taper- ing from the middle toward the anterior end ; suture impressed, and upon the proximal side of it there is an almost equally impressed revolving line, having the aspect of a second suture; folds of the columella well developed. Surface marked by the ordinary lines of growth and also upon the DE60KIPTIONS OF NEW SPECIES, 1 19 spire by numerous small longitudinal folds, parallel with the slightly oblique direction of the lines of growth. These folds appear upon the distal portion only of the last volution. Length of the largest example obtained, twenty-five millimeters; diam- eter of the body volution, twelve millimeters. This species differs from B. priscus Meek, with which it is associated in the less robust and more elongate form of the shell, its proportionally longer spire, more delicate and finer markings, and the less abrupt convexity of the volutions upon the proximal side of the suture. The specific name is given in honor of the author of the genus. Position and locality. — Point of Rocks Group; Bear River Valley, near Mellis Station, Wyoming. Genus PLANORBIS Guettard. Subgenus Bathyomphalus Agassiz. Planorbis (Bathyomphalus) Kanabensis (sp. nov.). — Shell rather small; spire flat or nearly so, suture impressed; volutions five or six, narrow, regularly increasing in size to the aperture, broadly convex upon the upper side ; periphery abrubtly rounded to the broadly convex under side, the latter extending obliquely downward and inward to the well defined, mod- erately broad, and deep umbilicus. Surface marked by ordinary lines of growth. Diameter of coil, twelve millimeters. Position and locality. — Point of Rocks Group; Upper Kanab, Utah. Genus PHYSA Draparnaud. Physa Kanabensis (sp. nov.). — Shell rather under the average size; very elongate ; spire extended ; volutions about six, broadly convex ; aperture very narrow, ending sharply at its distal end and abruptly rounded at the proximal end. The specimens of the collection are all imperfect, but the species is peculiarly distinguished by its very slender elongate form, its extended spire, spire, and its very narrow elongate aperture. Position and locality. — Point of Rocks Group; Upper Kanab, Utah. 120 INVEKTBI3KATE PALEONTOLOGY. [white. Genus HELIX Linnaeus. Helix Kanabcusis (sp. nov.). — Shell having- the general external shape and character of //. paUiata Say, but, besides being1 considerably smaller, it presents some differences in its aperture. Like that species, its lip is re- flexed, and it has a similar large tooth upon its parietal wall. In addition to the latter there are four short linear ridges upon the inner surface just within the upper and outer portion of the aperture, at the margin of which they terminate exteriorly, but extend inward in the direction of the whorl from two to three millimeters. The lowermost of these small ridges is shortest, but more prominent and tooth-like than the others. Only a single specimen was obtained, and that is very imperfect. It is described and named here because of its value as showing the great differentiation of Ilelecine types so early as the Cretaceous period. Position and locality. — Point of Rocks Group; Upper Kanab, Utah. Genus ANCHURA Conrad. Anchura ruida (sp. nov.). — Shell rather small ; spire moderately elon- gate ; volutions about seven, convex ; suture impressed ; wing moderately large, contorted, bearing at its extero-posterior corner a falciform process which points backward in the direction of the spire ; the outer border of this process and also that of the body of the wing continuously and broadly rounded to the extero-anterior corner of the wing, which is abruptly rounded ; thence the anterior border of the wing extends nearly straight inward to a somewhat broad curved sinus adjacent to the columella, which sinus corresponds to the anterior canal in other species; inner border of the falciform process broadly concave ; and between that process and the spire the distal border of the wing* is shortly concave and a little reflexed, sug- gestive of a broad posterior canal, especially as the anterior canal is more than usually broad; inner lip provided with a distinct callus, which in some cases at least extends beyond the distal end of the aperture across the next volution ; columella not much produced in front ; volutions of the spire marked by many longitudinally oblique folds, which extend to the suture on the proximal side of the volutions, but not much beyond the middle on the distal side, and do not appear at all on the body volution or wing. DESCRIPTIONS OF NEW SPECIES. 121 The whole surface marked by fine revolving stria', which are more distinct upon the last volution and wing-; last volution also marked by a moderately strong- revolving carina, which extends outward upon the wing" and is continued to the point of the falciform process. Length, sixteen millimeters; breadth across the body volution, includ- ing- the wing, twelve millimeters. This species resembles A. Americana Meek and Hay den in general form and surface markings, but it differs from that shell by its large anterior sinus, the inflection of the anterior border, and the reflexion of the posterior border of the wing, and also in the general shape of the wing. Position and locality. — Sulphur Creek Group; Upper Kanab, Utah.. Anchura prolabiata (sp. nov.). — Shell rather above medium size, sub- fusiform ; spire elongated and tapering, with nearly straight sides, to a point ; volutions, nine or ten, convex, the last one proportionally more en- larged than the others ; suture impressed ; wing large, broad, its outer border nearly straight or slightly convex, its anterior and posterior corners abruptly rounded ; posterior border bearing a strong, broad, blunt process about midway between the spire and the outer margin of the wing, the outer margin of the process having a direction parallel with that of the outer margin of the wing ; posterior border of the wing concave between the outer corner and the base of the process, and also regularly and con- tinuously concave from the spire to the end of the process ; anterior border of the wing broadly and regularly concave to the base of the anterior canal, which is apparently rather short. Inner lip unknown. Surface of the volutions of the spire marked by numerous vertical or slightly oblique folds or ridges, which disappear upon the body volution and wing ; these folds are crossed by numerous fine revolving raised lines, which are hardly visible without the aid of a lens, except those adjacent to the sutures, which are stronger ; these revolving lines are perceptible upon the body volution, but are very faint upon the wing. No revolving ridge passes out upon the wing from the body volution, such as is common upon shells of this genus. Length about four and a half centimeters ; breadth, measured across 122 INVERTEBRATE PALEONTOLOGY. [white. the wing and body volution, twenty-nine millimeters; diameter of the body volution, fifteen millimeters. This species differs from all others known to me by the projection of the outer border of the wing- beyond the posterior process. Position and locality. — -Sulphur Creek Group; Upper Kanab and Sink Spring, Utah. Genus LUNATIA Gray. Lunatia Utahensis (sp. nov.). — -Shell globose ; spire small, acute, but not much extended ; volutions about eight, the last one much inflated, suture moderately impressed ; aperture semilunar, somewhat abruptly rounded anteriorly, callus of the inner lip apparently not much thickened, but thicker anteriorly than posteriorly. Surface marked by the ordinary lines of growth. Length from the apex to the anterior end of the aperture about four centimeters; diameter about three centimeters. Position and locality. — Salt Wells Group; Coalville, Utah. Genus GONIOBASIS Lea. Goniobasis Cleburni (sp. nov.). — Shell large, gradually tapering from the last volution to the apex, the sides of the spire being only slightly convex; volutions apparently nine or ten, graduall}' increasing in size, the last one not being proportionally larger than the others; suture slightly impressed; sides of the volutions nearly flat or slightly convex, the outer and anterior sides of the last one broadly and regularly convex; aperture ovate; outer lip broadly sinuate. Surface of the spire marked by strong longitudinal or slightly flexed and oblique ridges or folds which disappear toward the aperture of the last volu- tion. Upon the anterior surface of the last volution beyond the distal end of the aperture, there are several slightly raised revolving lines, and the edges of the vertical plications are also sometimes seen to be faintly crenu- lated as if by incipient revolving lines. The specimens of the collection have all lost the apex, but the length of a full grown one is estimated at five centimeters; diameter of the last volution, nineteen millimeters. DESCRIPTIONS OF NEW SPECIES. 12 n This is the largest species of Goniobasis known to occur at the locality where it was found, and which has furnished three other distinct species. The specific name is given in honor of Mr. W. Cleburn, division en- gineer of the Union Pacific Railroad. Position and locality. — Point of Rocks Group ; Bear River Valley, near Mellis Station, Wyoming. Goniobasis chrysaloidea (sp. nov.). — Shell of medium size, gradually taper- ing from the last volution to the apex; volutions about seven or eight, those of the spire slightly convex, the last one broadly rounded to the anterior end; suture impressed, the apparent impression being increased by the pro- jecting fold of the distal edge of each volution, which is appressed against the proximal edge of the next preceding one. Surface marked by more or less distinct longitudinal, slightly bent folds, which are crossed by several revolving lines that appear only upon the folds and not between them, giving them a knotted or crenulated appearance; anterior surface of the last volution also marked by distinct raised revolving- lines. Length twenty-eight millimeters; diameter of the last volution, nine millimeters. This species differs from G. chrysalis Meek in its much larger size, much greater apical angle, straighter sides, and in the details of its ornamen- tation. Position and locality. — Point of Rocks Group ; Bear River Valley, near Mellis Station, Wyoming. Genus VIVIPARUS Montfort, Viviparus Panguitcliensis (sp. nov.). — -Shell elongate-trochiform ; spire considerably produced in the case of some of the examples, but less so in others, convex- conical, diminishing more rapidly near the apex than at the proximal half of the shell ; apex acute ; volutions about six, flattened upon the outer side, especially the last two volutions; anterior side of the last volution broadly rounded and forming a more or less distinct angle with the outer side; the distal side of each volution concave to receive the convex 124 INVERTEBRATE PALEONTOLOGY. [white. proximal side of the next preceding one, but projects a little beyond it so that an angular shoulder is formed upon the proximal side of the suture. Aperture subtrihedral in outline. Surface marked by the ordinary lines of growth, and also by numerous minute, raised revolving striae, upon both the outer and anterior sides of the volutions. There is considerable variation in the flattening of the outer side of the volutions in different examples and in different parts of the same example. The volutions near the apex of all the shells are usually convex and not much if at all flattened; in some cases the outer side of the last volution is broadly convex, while in others it is not only flattened but a little concave, especially the part nearest the suture. Length of an average sized example, thirty millimeters; diameter of the last volution, twenty millimeters. Genus ODONTOBASIS Meek. Odontobasis buccinoidea (sp. nov.). — Shell of medium size somewhat robust; volutions six or seven, regularly convex; suture faintly impressed; surface marked by somewhat strong longitudinal folds which end at the suture upon the proximal side of the volutions of the spire, but do not quite reach the suture upon the distal side, and upon the last volution they die out before reaching the anterior end of the shell; the whole surface also marked by somewhat coarse revolving raised lines, which in crossing the longitudinal folds give them a crenulated appearance. The revolving lines upon a narrow space on the proximal side of the suture, and also upon the space in front of the revolving furrow of the columella, are finer than the others. Odontoid process not very prominent, forming a small angular pro- jection at the end of the revolving furrow of the columella. Length, thirty-seven millimeters; diameter of the last volution, twenty- two millimeters; but these proportions vary considerably in different shells of the species. Position and locality. — Point of Rocks Group; two miles west of Point of Rocks, "Wyoming. i J CD DESCRIPTIONS OK NEW SPECIES. 125 TERTIARY PERIOD. Mollusca. Conchifera. Genus UNIO Retzius. Unio petrinus (sp. no v.). — Shell very large, transversely elongate, moder- ately thick; test massive; basal and dorsal margins subparallel; the latter broadly but slightly convex and the former nearly straight or faintly emargi- nate about, or a little behind the middle; front abruptly rounded; postero- dorsal and postero-basal margins somewhat abruptly rounded to the pos- terior margin, giving, in some cases, a subtruncate appearance to the posterior end of the shell; beaks depressed, situated near the anterior end; umbones broad; hinge massive, both cardinal and lateral teeth being very strong. Surface apparently marked in no other manner than by the ordinary lines and imbrications of growth. The outer prismatic layer is well preserved, and the umbones, like those of all the species of Unio I have examined, from the Mesozoic and Cenozoic strata of that region, appear to have suffered, while living, no erosion, such as is common in the case of the recent Unio- nidae of the Mississippi and its tributaries. Length of the largest example in the collection, fifteen centimeters ; height of the same, seven and a half centimeters. In the case of young examples the length is proportionally greater. This species may be readily distinguished from all others at all likely to be confounded with it by its great size, elongate form, and its subparallel dorsal and ventral margins. Position and locality. — Bitter Creek Group; Black Buttes, Wyoming. Unio proplieticus (sp. nov.). — Shell small or of medium size, obliquely subovate in marginal outline, moderately thick, the greatest thickness being a little below the umbones; test rather thick; umbones prominent, directed forward; beaks curved inward and forward, reaching as far as, or a little farther than, the front of the shell; front broad, nearly perpendicular; front 'margin slightly convex above, but abruptly rounded to the basal margin below; basal margin broadly rounded, or sometimes a little straightened at 12(5 INVERTEBRATE PALEONTOLOGY. [white. the middle; posterior extremity abruptly rounded; dorsal margin broadly rounded obliquely downward to the posterior extremity; the dorsum of each valve elevated and its margin flexed inward and downward to the cardinal ligament, so that the latter is hidden from sight by side view of the shell. Surface marked by the ordinary lines of growth and by numerous fine radiating striae, which appear also in the substance of exfoliated portions of the test. Length, five centimeters; height from base to umbones, thirty-seven millimeters. This species is of the type of U. clavus Lamarck, which it much resem- bles in general aspect. It is so different from any other known species of Unio in the Tertiary rocks of America that it cannot be mistaken for any of them. Position and locality. — Bitter Creek Group; Black Buttes, Wyoming. Unio brachyopisthus (sp. nov.).— Shell small or of medium size, some- what gibbous, subcircular in marginal outline, the length and height being about equal ; umbones broad, not prominent ; beaks depressed, situated near the middle of the dorsum ; postero-dorsal portion broad, depressed so that rounded umbonal ridges are formed, which extend to the postero-basal extremity, and the hinge ligament is hidden from sight by side view of the shell. Surface marked only by the ordinary lines and lamellations of* growth. Length and height of the largest example discovered, each forty -four millimeters. This species may be readily distinguished from all others by its sub- circular, marginal outline and its extremely short and abruptly-rounded posterior. The shortness of the posterior portion does not appear so con- spicuously in the young shell as in the adult, because the additions by growth are made more rapidly upon the basal and antero-basal borders than elsewhere. Position and locality— Bitter Creek Group ; Black Buttes, Wyoming. Unio Slioshonensis* (sp. nov.). — Shell of ordinary size, broadly subel- * The so-called tribal name is applied by the Indians theinselves to their country or laud, not to the tribe. DESCRIPTIONS OF NEW SPECIES. 127 liptical or subovate in marginal outline ; valves moderately and somewhat regularly convex ; test not massive ; dorsal margin broadly arched ; front margin regularly rounded ; basal margin broadly and regularly rounded ; posterior margin somewhat abruptly rounded, the postero-dnrsal portion sometimes obliquely truncated and sometimes sloping to a more prominent posterior extremity ; beaks well defined, but not prominent ; umbones broadly convex. Surface marked by the ordinary lines and lamellations of growth. Length of the largest example in the collection, nearly seven centi- meters ; height of the same, five centimeters. This species bears some resemblance to U. Haydeni Meek, from the Bridger Group, but differs from that species in its larger size, its convex instead of straight dorsal margin, its rather -more prominent umbones, and its greater proportionate height. Position and locality. — Upper Green River Group; Henry's Fork and Alkali Stage Station, Wyoming; also in Lower Green River Group; west side of Snake River, six miles north of Junction Mountain ; Cliffs, four miles northeastward from Vermilion Canon ; and Dry Mountains, North- western Colorado. Genus CORBICULA Muhlfeldt. Coroicula Powell i (sp. no v.). — Shell rather small, subelliptical in mar- ginal outline ; valves thin, slightly but somewhat uniformly convex ; beaks small, not prominent ; cardinal and lateral teeth well developed ; both anterior and posterior lateral teeth finely crenulated transversely ; middle cardinal tooth of each valve having a shallow vertical groove along its middle; a very faintly-raised ridge extends downward from beneath the beak on the inner surface of each valve, and dies out before reaching the base. Surface nearly smooth, but marked by fine lines of growth. Length, twenty-three millimeters ; height, from beak to base, fifteen millimeters ; thickness, eight millimeters. This shell differs from typical forms of Corbicida in its elliptical out- line, slight thickness, and in the delicacy of the test. All the species associated with it, except an oyster, are exclusively marine forms. ' 128 INVERTEBRATE PALEONTOLOGY. [white. Specific name given in honor of Prof. J. W. Powell, geologist in charge of the Second Division United States Geological and Geographical Survey. Position and locality. — Tertiary strata, probably late Eocene ; Bijou Basin, forty miles east of Denver, Colorado. Genus PISIDIUM Pfeiffer. Pisidium saginatimi (sp. nov.). — Shell small, subcircular in marginal outline ; anterior side slightly longer than the posterior ; valves inflated, the convexity from beak to base being sometimes irregular in consequence of one or more abrupt concentric flexures. Surface marked by ordinary lines of growth. Length, five millimeters ; height, five and a half millimeters ; thick- ness, five and a half millimeters. Position and locality. — Bitter Creek Group; Almy coal mines, near Evanston, Wyoming-. Genus MESODESMA Deshayes. Mesodesma Bisliopi (sp. nov.). — Shell small, subovate or subtrihedral in marginal outline, moderately gibbous ; umbonal ridges somewhat distinct, the posterior pair more so than the others ; umbones prominent ; beaks small ; both anterior and posterior lateral teeth well developed and trans- versely striated, as in Corbicula; cartilage pit beneath the beak small; car- dinal tooth in front of it rather small and V-shaped; pallial sinus deep; muscular scars distinct ; right valve unknown. Surface nearly smooth, and marked by very fine lines of growth. Length, about one centimeter ; height, about six millimeters. This shell differs from typical forms of Mesodesma in its V-shaped car- dinal tooth, transversely striated lateral teeth, and deep pallial sinus. Specific name given in honor of Prof. F. M. Bishop, of Salt Lake City, Utah. Position and locality. — Tertiary strata, probably late Eocene ; Bijou Basin, forty miles east of Denver, Colorado. DESCRIPTIONS OF NEW SPECIES. 129 Genus CORBULA Bruguiere. Corbula suhundtfera (sp. nov.).— Shell of ordinary size ; marginal out- line subtriheclral or subovate ; valves only slightly unequal ; beaks con- tiguous ■; umbones moderately prominent ; beaks incurved and directed a little forward; front obliquely truncate, concave, producing indistinctly defined anterior umbonal ridges; abruptly rounded below to the basal margin, which is broadly rounded ; posterior extremity low, prominent, and sharply rounded ; postero-dorsal margin sloping from the dorsum to the posterior extremity ; this margin of each valve is bent abruptly inward and downward, producing a narrow, shallow furrow, bordered at each side by a' somewhat prominent ridge, which extends from behind the beak to the posterior extremity of the shell. Surface marked by numerous, more or' less strongly elevated, con- centric folds, which disappear before reaching the anterior and posterior margins. Between these folds, and upon those parts of the surface unmarked by them, the surface is marked by ordinary lines of growth. Length, twenty-five millimeters ; height, eighteen millimeters. This species closely resembles C. undifer Meek, from the Point of Rocks Group at Rock Springs, Wyoming, but differs from that species in its less extended posterior extremity, its less angular posterior umbonal ridges, its less sharply elevated, concentric folds, and in wanting the peculiar flattening of the umbones between the posterior and anterior umbonal ridges which that species possesses. Position and locality.— Bitter Creek Group; Point of Rocks, Wyoming. Gasteropoda. Genus SUCCINEA Draparnaud. Succinea papillispira (sp. nov.).— Shell rather small, ovate or subelliptical in lateral outline; spire minute but prominent; last volution much expanded and broadly convex. Surface marked by the ordinary lines of growth, and, under a lens, faint, close-set, revolving striae are to be seen. Length, eleven millimeters; breadth of aperture, six millimeters. 9p G ]30 INVERTEBRATE PALEONTOLOGY. [white. This species possesses peculiar interest from the fact that it is the first Succwea that has been discovered in the Tertiary strata of that great region. Although there are so few salient, specific characters in any species of the genus, this shell may be readily recognized by its minute spire, the length of which is only a very small part of the full length of the shell, and also by its broadly convex last volution. Position and locality. — Upper Green River Group; Alkali Stage Station, twenty-two miles northwward from Green River Station, Wyoming. Genus HELIX Linnaeus. Helix riparia (sp. no v.). — Shell of medium size, subcorneal; volutions about five, moderately convex; suture slightly impressed; spire considerably produced for a species of this genus, equal in length to about three-sevenths of the entire length of the shell; proximal side of the last volution broadly and continuously rounded from the outer side; umbilicus small, rather deep; outer lip unknown; aperture oblique, broadly subovate in outline. Surface marked by the ordinary distinct lines of growth. Position and locality. — Lower Green River Group; eight miles below Green River Station, Wyoming. Helix periplieria (sp. nov.). — Shell of ordinary size, sublenticular in form; spire low and broadly convex; volutions about five, each broadly convex between the sutures; the last volution abruptly, almost angularly, rounded at the periphery of the shell; under side broadly convex and rounded sharply into a small, deep umbilicus. Lip apparently not reflexed. Surface marked by the ordinary distinct lilies of growth. Peripheral diameter, about fifteen millimeters. Position and locality. — Bitter Creek Group; south base of Pine Valley Mountains, Utah. Genus PUPA Lamarck. Pupa incolata (sp. nov.). — Shell small, turreted, regularly tapering to the apex; volutions about six, convex, regularly increasing in size to the aperture, the last one not being contracted; suture impressed; aperture sub- ovate in outline, its length a little more than one-third that of the whole shell; outer lip thickened, reflexed. DESCRIPTIONS OF NEW SPECIES. 131 Length, five millimeters; diameter of last volution, two millimeters. This species is of about the same size as the recent species Pupa fullux Say, and closely resembles it in form and general character. Position and locality. — Upper Green River Group; Henry's Fork, Wyo- ming, where it is associated with the following species: Pupa arenula (sp. nov.). — Shell minute, ovate; volutions five or six, con- vex; suture impressed; aperture contracted; teeth of the aperture unknown. Length, two millimeters. This shell is of about the same size and shape as Vertigo ovata Say, and in general aspect it closely resembles that species. It appears, however, to be a true pupa; at least the characters which should separate it from that genus are not apparent. Position and locality. — Upper Green River Group; Henry's Fork, Wyo- ming. Genus NERITINA Lamarck. Nerit'ma volvilineata (sp. nov.). — Shell small, subovate in lateral outline; volutions three and a half or four, regularly convex; spire short, as is common in this genus, but somewhat prominent; suture slightly impressed; aperture semilunar; inner lip broad, plain, flat, its inner edge not clearly seen, but if crenulated at all, it is not conspicuously so. Surface marked by numerous raised, revolving lines of unequal size, which increase in number by implantation as the volutions increase in size; the revolving lines crossed by the usual lines of growth, which give the surface, upon some parts, at least, an indistinctly cancellated appearance under the lens. Greatest diameter of the largest example discovered, nine millimeters; height, lying with its aperture upon the table, five millimeters. Position and locality. — Bitter Creek Group; Black Buttes, Wyoming. Genus MELANIA Lamarck. Mclania Larunda (sp. nov.). — Shell large, elongate; volutions apparently eleven or twelve, uniformly increasing in size, moderately convex, bearing a revolving row of prominent, strong, outward projecting, laterally sharp- ened tubercles, which extend from the apex to the aperture; suture linear; 132 INVERTEBRATE PALEONTOLOGY. [white. surface of the- volutions on the distal side of the row of tubercles without revolving stria), or having one or two indistinct ones; surface upon the prox- imal side of the row of tubercles marked by numerous elevated, slightly waved, revolving striae, which are more distinct about midway of the. space than elsewhere, and are very close together near the columella. Only three or four of these stria3 appear upon the volutions of the spire, because the remainder are covered by each succeeding volution. Aperture oval or sub- elliptical; outer lip having a broad, shallow notch, the retreating angle of which is opposite the row of tubercles, anterior portion moderately extended and abruptly rounded to the columella. Length, about nine and a half centimeters, when entire ; diameter of the last volution, twenty-two millimeters. This species is more nearly like a true Melania of Old World type than any of the so-called Melanians of North America with which I am ac- quainted. Position and locality. — Tertiary strata ; Grow Creek, Colorado, where it was obtained by Mr. W. Cleburn. Genus HYDROBIA Hartmann. Hydrobia recta (sp. nov.). — Shell small, very slender, sides of the spire straight ; volutions convex, apparently twelve or more, increasing regularly and uniformly in size from apex to aperture. Surface marked by the ordinary lines of growth. Length of one example in the collection, nine millimeters ; diameter of the last volution of the same, one and a half millimeters. Other exam- ples indicate a length nearly twice as. great as that here given. Position and locality. — Bitter Creek Group ; Almy coal-mines, near Evanston, Wyoming. Hydrobia Utahensis (sp. nov.). — Shell rather small, elongate-conical, spire moderately produced, its sides straight or nearly so ; volutions about six, convex ; suture impressed ; aperture ovate, a little longer than wide, its distal extremity slightly angular, its anterior end prominent and rounded. Surface marked by the ordinary lines of growth. DESCRIPTIONS OF NEW SPECIES. 133 Length, about five millimeters ; diameter of the last volution, nearly two millimeters. Position and locality. — Bitter Creek Group ; west base of Mu-si-ni-a Plateau, 1,000 feet below the summit, Utah. Genus VIVIPARUS Montfort, Viviparus plicapressus (sp. nov.). — Shell rather under medium size ; spire, conical ; sides nearly straight ; volutions about seven, convex, the outer and anterior convexity of the last one continuous^and uniform ; suture impressed. At the distal side of each volution there is a small, more or less distinct, revolving groove or furrow, by which that part is folded and closely appressed against the proximal side of the adjacent volution, the fold form- ing a slight projection upon the proximal side of the suture. Surface marked by the ordinary lines of growth, and upon some examples there appears a faintly raised revolving line or incipient angulation near the middle of the outer side of the volutions. Length, about twenty-five millimeters ; breadth of last volution, twelve millimeters. Position and locality. — Bitter Creek Group ; Black Buttes, Wyoming. Genus LEIOPLAX Troschel. Leioplax t turricula (sp. nov.). — Shell of ordinary size, elongate conical ; volutions about eight, gradually increasing in size ; convex angular, the angle being sharp, prominent, and situated a little in advance of the middle of the side of the volutions of the spire ; suture slightly impressed ; last volution broadly rounded from the revolving angle to the umbilicus ; umbil- icus narrow, deep and marked within by two or three revolving lines. Sur- face upon both sides of the revolving angle of the volutions marked more or less distinctly by two or three revolving raised lines. Length, thirty millimeters ; diameter of last volution, fifteen millime- ters. This shell has the aspect of some forms of Goniobasis, but the presence of an umbilicus excludes it from that genus. It also varies from the typical forms of Leioplax, but appears to be more nearly related to this than 134 INVERTEBRATE PALEONTOLOGY. [white. to tiny other established genus and is accordingly referred to it provision- ally. Position and locality. — Bitter Creek Group ; Black Buttes, Wyoming. Genus TULOTOMA Haldeman. Tidotoma Thmnjpsoni (sp. now). — Shell moderately large, having the general form of shells of this genus; spire elevated, its sides broadly convex; volutions six or seven, their outer side flattened or only slightly convex; proximal side of the last volution also flattened or slightly convex, produc- ing a more or less prominent revolving angle between them; suture linear or faintly impressed ; umbilical chink minute or wanting. Surface of the three or four first volutions of the spire convex and unmarked, except by the ordinary lines of growth, but the last two or three volutions are con- spicuously marked by prominent tubercles in two or three revolving rows, extending to the aperture, and which sometimes seem to be connected in their respective rows by slightly raised revolving lines. The distal row of tubercles is strongest and is situated near the suture, on its proximal side. The proximal row is immediately upon the distal side of the suture, the tubercles of which are more elongated transversely than the others, but not so prominent, Between these two rows there is sometimes another obscure one, but upon some shells it is reduced to only a raised line. Length of a large example, thirty-eight millimeters ; diameter of the last volution, twenty-five millimeters. This shell resembles the recent species T. magnified Conrad, but differs from that shell in its more convex volutions, its faintly impressed suture, and the different arrangement of its tubercles. It also resembles T. ( Viviparus) Strossmayeriana Pilar, as published by Brusina, but differs in the less con- vexity of its volutions, especially the proximal side, and in the different character and position of the tubercles that adorn its surface. Genus PHORUS Montfort, PJiorus exoneratus (sp. nov.). — Shell small, concavo-convex, the convexity of the upper side being slight and nearly uniform ; volutions one and a halt or two; suture not distinctly shown; surface apparently quite plain or marked DESCRIPTIONS OF NEW SPECIES. 135 only by lines of growth; without extraneous bodies attached to the periphery; aperture very oblique and very narrow. Diameter of the shell, thirteen millimeters. Position and locality. — Tertiary strata, probably late Eocene; Bijou Basin, forty miles east of Denver, Colorado. CHAPTER IV. GEOGRAPHIC DISTRIBUTION OF THE GEOLOGICAL FORMATIONS IN THE UINTA MOUNTAINS AND A DISTRICT OF COUNTRY ADJACENT THERETO. I propose to give a brief description of the geology of a part of the Uinta Mountains and a district of country lying to the north, stretching beyond the Union Pacific Railroad. The region is embraced within the meridians of 108° '40' and 109° 52 '.5 west longitude, and between the par- allels of 40° 15' and 41° 40' north latitude. The Green River runs through the middle of the district, having a general northerly and southerly course, but from which it deflects in great curves. The Uinta Mountains are composed of elevated valleys, tables, and peaks, the latter having a very irregular distribution, due to geological structure. The axis of the range is the axis of a great flexure, having a total displacement (or exhibiting an upheaval) of more than 30,000 feet. This flexure terminates on the east in the little valley separating the Uinta Mountains from Junction Mountain. The latter represents a short, abrupt, anticlinal flexure, having a north and south axis The Uinta uplift has brought up all of the Mesozoic and Carboniferous Groups with the Uinta Sandstone, and in one locality a still older group of rocks, viz, the Red Creek Quartzite, is exposed. On the flanks of the range, both to the north and south, Cenozoic groups are found. The grand Uinta displacement is only a flexure in its general characteristics, as the down-throw on the north side of the axis is, in some localities, in part produced by faulting; while on the south side of the axis faults are found having1 throws on the north side of the fissure. Thus the faults, instead of being* a part of the general RED GREEK QUAKTZITE. j 37 flexure of the slope, are opposed to it, and the faults themselves, in a part of their courses, change to flexures. In addition to the complications thus mentioned, there are other minor flexures within the greater. All of these complications will be spoken of further on. Within the district which I undertake to describe, another great flexure must be mentioned. This has a north and south axis, and brings to view in the region north of Aspen Mountain the Sulphur Creek Cretaceous. On the flanks of tins flexure we find the Salt Wells and Point of Rocks Creta- ceous, and the Bitter Creek, Lower Green River, Upper Green River and Bridger Tertiaries, all of which groups took part in the movement which made this flexure; but there is no evidence that the Brown's Park Group or the Bishop Mountain Conglomerate was involved in the movement. The southern extremity of the flexure is well seen at the head of Red Creek, where the rocks dipping south from the end of the Aspen flexure become horizontal, and again are turned up by the great Uinta flexure, thus forming a synclinal between the flank of the greater flexure and the end of the lesser. The characteri sties of this displacement also will be discussed here- after. I now proceed to describe the geographic distribution of the groups or formations in this district, and to give their general stratigraphic character- istics, and also to note some interesting facts concerning their conformities and unconformities. All of the groups of rocks tabulated in Chapter II are found within this area except the Grand Canon Group and the Grand Canon Schists. RED CREEK QUARTZITE. The only locality where this group has been found within the territory embraced in the discussion is in the vicinity of Red Creek, a small tributary of the Green River, emptying into the latter at the head or western end of Brown's Park. Its geographic extension is well shown on the map, and needs no further description. Red Creek separates Quartz Mountain and Mount Wheeler by a tor- tuous, flaring, craggy canon whose sides rise to an altitude of about 2,0U() feet above the creek, and here the interior structure of the group is revealed. 138 GEOGRAPHIC DISTRIBUTION. The group embraced under the name is the lowest horizon found within the region under discussion. It is composed in large part of a quartzite, very crystalline and white, and having the general aspect of virgin quartz. Only in a few places is the original granular structure apparent. Intimately associated with the quartzite are very irregular aggregations of hornblendic and micaceous schists, the latter sometimes bearing garnets. Originally these schists were perhaps argillaceous strata between the thicker strata of pure siliceous sandstone. The whole group has been greatly metamor- phosed, producing a crystallization that in many places has quite, and in the remainder almost, obliterated the original granular or sedimentary structure, so far as it is apparent to the naked eye. Besides this recrystallization they have been profoundly plicated, or I should rather say implicated. It is only in a general way that any original stratification can be observed. This original structure can best be seen when standing at some distance from the beds to be studied. Its relation to the Uinta Sandstone above it is exhibited in the lower end of the canon of Red Creek and along the escarpment which faces Brown's Park on the south side of Mount Wheeler, up the canon of an intermittent stream four miles farther west, and also up the canon of Wil- low Creek. Other facts relating to the junction of the two groups are seen on the summit of Quartz Mountain. These facts are as follows: A part of the Uinta Group,- which is later and higher, terminates abruptly against the quartzite. The thickness of the beds thus limited is about 8,000 feet, and as the beds are traced from the southward to this plane of junction they rapidly change from finer to coarser sediments, often appearing as conglom- erates in the vicinity of the quartzite; but the total thickness of the beds is not increased by the transition from finer to coarser sediments, though particular beds may thicken, such thickening being compensated by the thinning out or disappearance of others. In these conglomerates the coarser materials are of quartzite, hornblendic rock, &c, similar to those of the Red Creek Group, held in a matrix of siliceous, hornblendic and micaceous sands, which are quite ferruginous. The position of the quartzite is on the flank of the great Uinta flexure, not its axis, and the junction of the lower two or three thousand feet of the Uinta Sandstone with the quartzite is not RED CREEK QUARTZITE. 139 seen; while from two to three thousand feet of the upper members of the Uinta Sandstone were deposited over the summit of the quartzite. From these facts we may safely infer that this was a great headland of quartzite standing out in the old Uinta Sea from some island, or perhaps from the mainland ; that it rose above its waters as a lofty mountain, while from two to three thousand feet of these sandstones, whose junction with the quartzite is unseen, and while 8,000 feet of sandstone whose junction is seen, were deposited. Then this mountain headland was buried with two or three thousand feet of the upper members of the Uinta Group. During that great movement which began during Cenozoic time, and which has con- tinued intermittently unlil the present, and which has given us the Uinta upheaval, this quartzite behaved in a general way as an integral part of the sandstone, flexing when the sandstone flexed, and faulting when the sand- stone faulted. In the upper part of Figure 11 we have a diagram exhibiting U. Uinta Group, li. Red Creek Quartzite. C. Cretaceous. Fig. 11.— Section and diagram of the Red Crock Unconformity. the relation of these two groups as now seen; the lower part of the same figure represents a restoration of the same section to the position these two groups held prior to the inception of the Uinta upheaval. It will be seen that the old shore line, in vertical outline, was now a bold cliff against which' 140 GEOGRAPHIC DISTRIBUTION. the waves of the Uinta Sea dashed, forming- deep caverns in the mural rock, and then at other horizons was a retreating slope. A further study of the facts shows that on a horizontal plain the projecting rocks inclosed dee}) bays. But we must remember that as the beds were deposited denudation pro- gressed ; so that the slope seen does not represent it as it existed at any one time during the deposition of the beds, but only the slope which was finally produced. At the beginning of the Uinta epoch it must have been much steeper than it is represented in the diagram. About 10,000 feet of the Uinta Sandstone is found to have been de- posited against the old quartzite headland before it was buried by the upper members of the Uinta Group. Hence, this headland must have been at least 10,000 feet high; but doubtless the quartzite itself was steadily de- nuded during this time, and we may suppose that it wasted away by erosion above quite as rapidly as it was buried below. Certainly this supposition is not violent ; and this would lead to the conclusion that the great headland was 20,000 feet high at the time when the lowest known number of the Uinta Sandstone was formed. We may now with some degree of probability restore in imagination one feature of that ancient geography and see a mountain more gigantic in its proportions than any which now pierces the clouds floating over North America. Stand on the- great plain by the Platte River and look at Long's Peak; on it pile all that can be seen of Pike's Peak from the banks of the Arkansas, and over these place all of Gray's Peak that stands above the same plain, and the mountain thus, built up in imagination would not equal in altitude this quartzite mountain, whose feet were bathed in the old Unita Sea. Geologists have arrived at the conclu- sion that these quartzites and schistic rocks which appear over many portions of the earth were originally accumulated as sediments and subsequently metamorphosed. In the case of this group the metamorphism was anterior to the deposition of the sandstones as seen from the facts mentioned above, viz, that the sandstones are composed of material denued from the meta- morphic group. But the sandstones have great thickness and underlie un- conformably an extensive series of Carboniferous rocks. From this we infer that the quartzite is of great geological antiquity. DEVELOPMENT OF UINTA SANDSTONE. 141 UINTA GROUP. As shown by the map, the great mass of the Uinta Range is composed of sandstones of tills group. Intercalated with the sandstones some shales are found, the latter being arenaceous, with a small portion of argillaceous material. In a few places the sandstones have assumed a crystalline struc- ture, forming a quasi quartzite. The whole group is exceedingly ferruginous. Thin seams of clay ironstone are often seen to separate the strata of sand- stone, and many of the shales contain large quantities of iron. Many of the sandstones are seen to be ferruginous on the interior when broken, but some of the beds are buff and light gray on fresh surfaces. The general color of the walls of the canons and mountain escarpments is red and brown, due to the more complete oxidation of the iron. In the canons and gulches, where bays of quiet water are formed, considerable accumulations of steel- gray iron sands may often be seen. These sometime form a pigment which the Indians of the region were accustomed to use as paint in former days. The great mass of the sandstones are fine grained, but occasionally throughout the series strata of pebbles are found; near its junction with the Red Creek Quartzite these are conglomerates. Those peculiarities or markings of strata, known as ripple marks, are very abundant at many hori- zons from the top to the lowest known strata and mud rills, and rain drop impressions are sometimes found. A very few concretions have been found in the group. Weeks and months have been spent in the search yet no fos- sils have been found. Within the territory embraced in the description the base of the group is never seen. The Green River runs along the axis of the Uinta flexure for many miles but its bed is yet in the Uinta Sandstone so that it is impossible to determine the entire thickness of the group, but that which is exposed has a wonderful developement, no less than 12,500 feet of these sandstones and shales being seen. I have already stated my reasons for considering this formation to be older than Carboniferous, and I have given it provisionally a Devonian color on the map. Professor Marsh in his article in the American Journal of Science and Arts, in the March number of 1871, "On the geology of the eastern Uinta Mountains," in speaking of these formations says, " * * * * and a subsequent examination of apparently a portion of the same series, 142 GEOGRAPHIC DISTRIBUTION. on the western side of the river, rendered it probable that a part of them at least are of Silurian age." In that article the professor does not mention the finding of any fossils in the formation, and on what facts his statement is based I do not know ; but his conclusion is entitled to great consideration, for, although his study of this region was of short duration, he fully appre- ciated the great series of formations brought into view by the Uinta upheaval, and in clear comprehensive language gives, in the article mentioned, a sum- mary statement of the structural geology of the eastern Uintas. The following section was made by Mr. John F. Steward in the sum- mer of 1871. It commences at Beehive Point at the head of Red Canon and ends at the foot of the canon where the river debouches into Brown's Park. Lower members of the group are seen farther down the river but are not brought into the section. UNITA SANDSTONE. 143 Fig. 12.— SECTION OF UINTA SANDSTONE EXPOSED IN RED CANON. •0,(100 3 T-r Xo. 1, 420 feet. Arena- ceous shales and Hand- stones; gray, pink, and brown. No. 2, 285 feet. Sand- stones andarenaceons sbales. a, 2 feet. Sandstones ; dark brown. 6, 4 feet. Sbales ; not well exposed. c, 3 feet. Sandstones ; gray ; coarse ; break - iug into irregular fragments on expos- are to the weather. d, CO feet. Sandstones ; dark red ; not well exposed. e, 7 feet. Sandstones ; pinkish-gray; thinly and irregularly lam- " inatod. /, 13 feet. Arenaceous sbales ; dark purple; very friable. c o0"oao ' f* ..** S\ rm „i *> *. r »o o. 10, 000 144 GEOGRAPHIC DISTRIBUTION. A good section can be obtained by passing- over the O-wi-yn-knts plateau. On the northeast, this plateau culminates in a high ridge of cherty and brecciated limestone which is the base of the Red Wall Group. By starting at the eastern extremity and foot of this ridge and going south west- ward across the plateau and descending into Brown's Park until the axis ot the flexure is readied, yon pass over the upturned edges of the Uinta Sand- stone. This section gives a thickness to the beds of more than 13,000 feet. The factors used in the measurement were the distance between the extrem- ities of the line along which the section was made as determined by the topographers, and the observed dips along the line at snbecpial distances of about 200 yards. In 1871 we attempted to make a section from the axis, through the Cation of Lodore, but the difficulty of navigating the river was so great that we conld not perform the task with satisfaction; but the thick- ness of the beds found along this line was not less than 13,000 feet. The Uinta Sandstone crops out along the base of the wall through the upper part of Whirlpool Canon. On the north side of the Yampa Plateau, south of the Yampa River there is a monoclinal flexure and fault by which the Carboniferous rocks are uplifted several thousand feet. There are three canons running across this displacement which cut through the Carbonif- erous rocks and reveal in their walls several hundred feet of the upper members of the Uinta Group. The anticlinal uplift which forms Junction Mountain is bisected by the Yampa River. The gorge through which the river runs is called Junction Mountain Canon. In the heart of the cation Uinta Sandstones are seen. UNCONFORMITY AT THE SUMMIT OF THE UINTA GROUP. A period of erosion or dry land condition intervened between the deposi- tion of the Uinta Sandstones and of the Carboniferous Groups. In Whirlpool Canon the red sandstones of the Uinta Group are thrust up into the sandstones and shales of the Lodore Group, and in some cases almost sever them; that is, the Uinta Sandstones were deeply eroded into abrupt valleys with steep cliffs, some of them 400 feet high, anterior to the deposition of the Lodore Group. There is a difference of dip between the UNCONFORMITY OF THE SUMMIT "OP THE UINTA GROUP. 145 two groups of about four degrees, the lower group having the greater incli- nation to the south. The following section illustrates the facts observed here: 1,000 5,000 feet. E. Red Wall Group. L. Lodorc Group. V. Uinta Group. Fig. 13. — Section showing the unconformity between the Lodore and Uinta Groups in Whirlpool Canon. At the foot of the Canon of Lodore the unconformity is represented by a difference of dip of from 5 to 6 degrees, -and the Lodore Group steadily overlaps the upper members of the Uinta Group, cutting off more than 2,000 feet of the latter. Here, also, the Uinta Sandstone is protruded into the Lodore shales. These facts are illustrated in the following1 section : 0 5.000 feet. M. Red Wall Group. L. Lodore Group. U. Uinta Group. Fig. 14. — Section showing the unconformity between the Lodore and Uinta Groups in tbe Canon of Lodore. On the northeast side of the O-wi-yu-kuts Plateau the Lodore Group is wanting, and the massive limestone at the base of the Red Wall Group rests upon the Uinta Sandstone. In passing from the northwest end of the ridge along the strike of the sandstone to the southeast, the upper beds of the Uinta Sandstone are seen to disappear, having been cut off by erosion before the deposition of the limestone, and there is from one to two thou- sand feet more of the Uinta Sandstone at the former end of the ridge than at the latter. ' This unconformity can also be seen in the canon of Junction Mountain, and it has been observed on the southern side of the Uinta Mountains, west of the district covered by the map, in the canon cut by the tributaries of the Uinta River. 10 PG 146 GEOGRAPHIC DISTRIBUTION. THE CARBONIFEROUS GROUPS. CERTAIN GEOGRAPHIC DISTRICTS DESIGNATED. In describing the geographic distribution of the Carboniferous and Mesozoic Groups it will be found convenient to designate under general terms certain districts of country, as follows : FLAMING GORGE DISTRICT. There is a belt of country, extending from Bruce Mountain westward to the border of the map, where most of the Carboniferous and Mesozoic and certain of the Cenozoic formations are turned up on edge, so that in a limited area nearly all these groups can be studied. The Green River enters the Uinta Mountains by a flaring, brilliant, vermilion gorge, a conspicuous and well known locality, to which, several years ago, I gave the name Flaming Gorge, and this name has been generally accepted. I shall call this the Flaming Gorge district, PO CANON DISTRICT. East of Bruce Mountain, for many miles, the Uinta displacement is chiefly by faulting, and with slight exception the Carboniferous and Meso- zoic Groups have been carried down and are concealed. But southeast from Diamond Peak the displacement changes again into a flexure, and.once more the Carboniferous and Mesozoic Groups are found turned up on edge. This region is at the eastern end of the O-wi-yu-kuts Plateau, the plateau itself culminating in a high monoclinal ridge at its eastern extremity, and the plateau is bounded on this side by a deep monoclinal canon which divides it from a region of Mesozoic and higher Carboniferous hogbacks. This canon is also a well marked and well known geographic feature. Some years ago I gave it the name Po Canon, and that name has been accepted throughout the country. This I shall call the Po Canon district. YAMPA DISTRICT. In the Yampa Plateau by a series of flexures and faults the whole Meso- zoic and Carboniferous series are brought to view. East from the Yampa Plateau there is a simple anticlinal upheaval where all these groups are CERTAIN GEOGEAPIC DISTRICTS DESIGNATED. 147 again seen. I shall call the Yampa Plateau and adjacent country, together with the region embraced in the Junction Mountain uplift, the Yampa dis- trict. ISLAND PARK DISTRICT. Finally, west of the lower end of the Canon of Lodore and Whirlpool Canon there is a zone stretching to the westward where all these groups are in like manner exposed. At the foot of Whirlpool Canon lies the beau- tiful valley known as Island Park, which is embraced in this zone. I shall call this the Island Park district. LODORE GROUP. This group of rocks is seen in Lodore Canon, from which locality it takes its name. Here it fills valleys in the- Uinta Sandstone and buries the ancient cliffs and hills of the dry land period. These facts were set forth in the last section. The group is composed of soft sandstones and shales with conglomerates at the base and against the ancient hill sides. Its outcrop on the northwest side of the canon is of very limited extent and is not represented on the map, but on the southeast side of the canon it mounts the wall for several miles and appears in Dunn's Cliff, where its thickness was measured and found to be 460 feet. Its outcrop is represented on the map by a narrow .line. On the north side of the Uinta Mountains these rocks have been seen at but one point, viz, a little west of Beehive Point, and there is some uncertainty about this observation. Carboniferous fossils have been found in these beds. The area of the outcrop at the bottom of Whirlpool Canon is so narrow that the color has not been introduced on the map in that locality. RED WALL GROUP. Extensive outcrops of the Red Wall Group are found on the flanks of the Uinta Mountains. On the north side the entire group is composed chiefly of limestone, many of the beds being cherty. On the south side of the mountains many sandstones are intercalated with the limestone. About ten miles from Flaming Gorge in a southwestely direction, these beds are found dipping to the north, and as they are followed along the strike to the 148 GEOGRAPHIC DISTRIBUTION. westward they are seen to rise in a high monoclinal ridge. This ridge is not well developed until we pass beyond the area embraced on the map. Another outcrop is seen on the northwest corner of the O-wi-yu-kuts Pla- teau ; here the beds are standing vertically. On the eastern end of the same plateau, in the Po Canon district, another outcrop appears where the beds dip a little north of east in a lofty monoclinal ridge. The central mass of Junction Mountain is Red Wall limestone, and the group crops out in an unbroken but irregular zone along the south side of the Uinta Mountains on the east side of the Canon of Lodore, in the Escalante Peaks, and on the west side of the Canon of Lodore in the Island Park district. The Ti-ra-yu-kuts like the Escalante Peaks are composed of the hard cherty limestones of the Red Wall Group and are true flanking peaks. Here the beds all dip to the south usually at a rather low angle, and along the northern margin of the outcrop the cherty limestones stand in peaks. Another outcrop is seen at the bot- tom of Split Mountain Canon, and, last, these limestones are exposed on the Yampa Plateau on an escarpment formed by a fault or a monoclinal flexure which faces the Yampa River, and which is crowned by many towering peaks. All these outcrops are well represented on the map. LOWER AUBREY GROUP. This group is made up of rather soft sandstones with intercalated lime- stones; altogether the rocks are much more friable than the last mentioned group, and they also yield much more readily to atmospheric degradation than the beds of the Upper Aubrey. . Where the beds of the Red Wall and Upper Aubrey Groups stand in monoclinal ridges the beds of the Lower Aubrey are found in the inter-ridge or valley spaces. It is seen outcropping in the vicinity of Flaming Gorge and extending in a narrow zone westward beyond the region embraced on the map. On the east side of the O-wi-yu- kuts Plateau its outcrop can be traced along the eastern base of the mono- clinal ridge, which is composed of Red Wall limestones as described above. Here the valley lies between the two monoclinal ridges and is known as Po Caiion. Thpse beds are also found on both flanks of the Yampa Plateau and along the southern slope of the Uinta Mountains from its eastern extrem- LOWER AUBREY— UPPER AUBREY. 149 ity in a narrow'zone to the western border of the region under discussion. These beds outcrop again in Split Mountain Canon in a deep gulch running westward from its head, and again on the Yampa Plateau. Here some of its harder limestones are occasionally found standing in low peaks. UPPER AUBREY GROUP. In the Uinta Mountains the Upper Aubrey is composed of two mem- bers, a massive, homogeneous,, light gray sandstone at the base, which I have called the Yampa Sandstone, having a thickness of a thousand feet or more; and above, a cherty limestone from 150 to 200 feet in thickness, which I have called the Bellerophon Limestone. These beds from their indura- tion and homogeneity are well adapted to the formation of ridges. The group is seen outcropping in the Flaming Gorge district, and in a zone stretching westward from Horseshoe Canon for many miles. A little patch has been caught in the fault on the west side of Quartz Mountain and thrust between strata of Cretaceous Age, and its area is marked on the map. The monoclinal ridge on the east side of Po Canon is of this age. It is seen on all sides of Junction Mountain. Yampa Canon is carved through this sandstone. Here the rocks dip to the south and the homogeneous Yampa Sandstone on the north side of the canon is cut by a multitude of little can- ons, the channels of rainy day brooks. The entire slope is minutely carved in this manner and the spaces between the meandering cafions in many places are but narrow Avails, and sometimes these walls are broken where the channels approach too closely, and by this process buttes with narrow bases, and towers and pinnacles are formed. Along the courses of these intermittent streams great numbers of pot-holes are found. This topography is too minute to be represented on the map. On the eastern end of the Yampa Plateau this sandstone forms the slope of the plateau where it de- scends into the valley, and is in like manner carved with innumerable gulches whose courses are interrupted by pot-holes. This group has an extensive outcrop in the Yampa Plateau, and finally it has been traced from Whirlpool Canon westward beyond the limits of the map. * * * * * * * 150 GEOGRAPHIC DISTRIBUTION. The outcrop of these Carboniferous groups has been traced from point to point throughout the areas described above. In most places the exposures are complete and the relations of the beds can be well understood, and nowhere has any unconformity between its members been observed. Nor has any unconformity between the Upper Aubrey and the lower Mesozoic been observed; but as the lowest beds of Mesozoic Age are of very friable ma- terial, the exact junction is rarely seen. In the line of the fault between the Flaming Gorge district and the Po Canon district there is a fragment of Red Wall limestone, as seen on the map, ojfi the northwest corner of the O-wi-yu-kuts Plateau, which was not carried down by the fault ; i. e., the fault is to the north. JURA TRIAS GROUPS. SHINAKUMP GROUP. These beds are shales and soft sandstones, and hence in this region, which is plicated, they are found in valley spaces. The Lower Aubrey on one side and the Vermilion Cliff on the other stand in ridges. At the foot of the cliff on the south side of Flaming Gorge the Green River runs into the beds of this age and soon passes across them to enter the Upper Aubrey beds. Looking westward a towering cliff is seen on the right and a broken slope on the left and a narrow valley immediately in front, which may be followed until the bank of Sheep Creek is reached ; then turning up Sheep Creek that stream is found to run nearly its entire course, as represented on the map, in beds of this age. The steep wall of vermilion sandstone on the north side of this valley is, except at one point, an'impassable barrier. Eastward from Flaming Gorge the outcrop of the Shinarump Group is seen in a narrow valley between two ridges, for about six miles, until it is cut off by the great Uinta fault. Outcrops are also found in the Po Canon district. Here again the beds are found in the spaces between the ridges. The same is true along the foot of the Yampa Plateau to the east, south, and west ; and also in a general way in its outcrop from, the foot of Whirlpool Canon through the Island Park district. But this topographic peculiarity is not shown on the map in JURA TRIAS GROUPS. 151 the last mentioned region, as the area of the outcrop of all of the Jura Trias beds has its topography cut up so minutely by reason of many minor dis- placements and transverse lines of erosion that only a generalized represen- tation could be given. There is an island of Shinarump beds south of Echo Park, lying at the foot of the Yampa Plateau. VERMILION CLIFF, WHITE CLIFF, AND FLAMING GORGE GROUPS In this region the Vermilion Cliff and White Cliff Groups are massive sandstones, and hence stand in monoclinal ridges. Sometimes the base of the White Cliff Group is a series of softer beds, and two ridges are formed. Elsewhere the White Cliff Group rises high over the Vermilion Cliff beds in a wall which faces the axis of the Uinta upheaval on either side. Through- out this entire region the White Cliff sandstone is lighter colored than the Vermilion Cliff Group and everywhere exhibits that oblique structure known as false bedding. The Flaming Gorge Group with its limestones and sandstones is of heterogeneous stratification and breaks down into comparatively low hills, which are found on the backs of the great White Cliff ridges. The area of outcrop is parallel and coextensive with that of the Shinarump Group, except in the region near Flaming Gorge and the district immediately south of Echo Park. About UDur miles southeast from Diamond Peak there is a small outcrop of the Flaming Gorge beds standing on edge, with the summit of the group facing the plateau or axis of the Uinta upheaval. It is an interesting fact that the bad-land sandstones of the Flaming Gorge Group, both above and below the Mid-Group Limestone, are of fresh- water origin. The following is a section of the Jura Trias groups, made in the hills and cliffs west of Flaming Gorge and beginning above at the base of the conglomerate which underlies the teleost shales, and extending to the summit of the Bellerophon Limestone. In this region the limits of the section can be easily determined. 152 GEOGRAPHIC DISTRIBUTION. SECTION OF THE JURA TRIAS GROUPS. FLAMING GORGE GROUP. No. 1, 110 feet. — Gray, greenish gray, pink, purple, and chocolate beds ; very friable ; bad -land beds. No. 2, 200 feet. — Bluish-gray limestone; Mid-Group Limestone. No. 3, 500 feet. — Coarse red sandstone ; (unio beds.) No. 4, 250 feet. — Limestone; bluish-buff; compact; sometimes shaly and interstratified with orange shales and thin beds of gypsum. WHITE CLIFF GROUP. No. 5, 1,025 feet. — Massive sandstone; light gray and light orange, everywhere exhibiting false stratification in many directions and at many angles. VERMILION CLIFF GROUP. No. 6, 300 feet. — Sandstone ; massively bedded ; gray, drab, and brown within, but weathering with bright vermilion surfaces ; well exposed on the summit of Flaming Gorge. No. 7, 6 feet. — Shales, somewhat argillaceous. No. 8, 359 feet. — Sandstones ; rather friable, with intercalated shales ; the latter containing much gypsum ; weathering in variegated bright colors. SHINARUMP GROUP. No. 9, 1,095 feet, — Shales and sandstones containing much gypsum; weathering in man y colors, but brown and chocolate tints prevailing; in many places constituting bad-land beds. These beds all dip to the north at a great angle. It will be seen that the Jura Trias groups are exposed in outcrops on the north side of the Uinta Mountains in isolated patches, and these out- cropping beds in the Flaming Gorge district dip to the northward. In the Po Canon district they dip in a direction a little north of east. These two areas of outcrop are separated by a long space where these groups are earned down by the great Uinta fault, and their non-appearance at the surface is due ^ THE CRETACEOUS GROUrS. 153 chiefly to this cause, as they are not usually covered on this side of the range by unconformable Tertiaries. The exceptions will be noted hereafter. On the eastern end of the Uinta Mountains, between the Po Canon district and the Junction Mountain region, the upturned edges of Jura Trias rocks occasionally protrude through the overlying unconformable beds of Brown's Park age, but these protruding masses are too small to be shown on the map. About the Junction Mountain uplift the eroded edges of the Trias are sometimes buried beneath unconformable beds of Brown's Park age. On the south side of the Uinta Mountains the area of outcrop of the Jura Trias groups is very much greater. Near the head of Ashley's Creek the three upper groups of the Jura Trias are buried by unconformable rocks of Tertiary Age. Farther west, beyond the area covered by the map, these unconformable Tertiary rocks ride high up on the groups of Carboniferous beds. THE CRETACEOUS GROUPS. The Henry's Fork Group, which is the lowest Cretaceous formation, has an outcrop parallel and approximately co-extensive with the several groups of Jura Trias; that is, like those groups it was brought up by the great Uinta upheaval and the elevation of the Yampa Plateau. The same is true of the higher Cretaceous groups, but the latter are also brought into view in the Aspen Mountain upheaval ; and hence, in the discussion of the geographic distribution of these formations it is necessary to refer to a dis- trict of country not heretofore mentioned in connection with the Carbon- iferous or Jura Trias groups. I shall call this the Aspen Mountain district. henry's fork group. Nothing further need be said of the geographic occurrence of this form- ation. The group is composed of sandstones, indurated arenaceous shales, and conglomerates. These shales ring under the hammer, and are of steel- gray color, and rarely afford footing to vegetation, and can be traced in a bright band everywhere through the outcrop of the formation. The con- glomerates contain many gravels and bowlders of pre-existing schistic rocks. 154 GEOGRAPHIC DISTRIBUTION. They have a much more extensive development on the south than on the north side of the Uinta Mountains. On the south side of the Yampa Plateau, where the Fox Creek and Cliff Creek flexures unite, these conglomerates stand on edge with a dip of about 85 degrees to the southeast, and are firmly cemented, and stand as high walls, separated by a long, narrow valley, strewn with fragments of the conglomerate which have tumbled down from either side. Farther east, along the southern slope of the Yampa Plateau, they are very conspicuous features in the topography, as they are found standing in ridges and monu- ments. Here the topography is exceedingly complex, too much so to be rep- resented on the map which presents but a crude generalization of the many wonderful features of this region. SULPHUR CEEEK GROUP. These beds are soft argillaceous and arenaceous shales of dark color, but sometimes weathering a light gray. By reason of their exceeding fria- bility the areas of outcrop are everywhere valley regions, often diversified with broad stretches of low, bad-land hills in many places quite naked of vegetation, but elsewhere covered with patches of cactacece. Conspicuous among these is a species of opuntia, with its minute, subtle thorns hedging the hills with a threat of festering wounds. Its most extensive area of outcrop is in the Island Park sag, and it has a small outcrop in the northern portion of the Aspen Mountain uplift. A fragment of these beds is seen southeast of Diamond Peak, which, with a fragment of the Flaming Gorge beds on one side and a fragment of Salt Wells on the other, is standing on edge. It will be noticed that these beds dip toward the axis of upheaval, that is, the highest beds are found nearest the mountain, and they all stand with an inclination from the horizon of 90 degrees. SALT WELLS GROUP. It is unnecessary to speak in detail of the outcrop of the Salt Wells beds, as the attention of the reader has already been called to the outcrop on the flanks of the Uinta Mountains and in the Aspen Mountain district. It is worthy of remark that in the Uinta Mountain region these beds are THE CRETACEOUS GROUPS. 155 usually friable arenaceous and argillaceous shales, while in the Aspen Mountain district they are arenaceous shales and thinly bedded sandstones, and the greater induration of some of the beds in the last mentioned dis- trict causes the valley spaces, which are characteristic of this group, t,o be diversified with low ridges and cliffs. POINT OF EOCKS GROUP. The beds of this group can usually be divided into three somewhat well denned members, the Upper Hogback, Middle Hogback, and Golden Wall Sandstones, which are usually separated by a few feet of shaly sand- stones, and these stratigraphic characteristics under conditions of upheaval and erosion usually result in the production of three ridges, which are the topographic features giving names to the several members. The upper sandstone is usually massive and of light gray color weathering unequally on exposed surfaces, which inequality is not determined by lines of stratifi- cation. Here an irregular mass tumbles down and a cave is formed ; there an irregular mass is more indurated than the general body to which it belongs and stands in relief, often in some fantastic form ; and such weathering gives the cliffs which are usually found along the outcrop of these beds a strange and weird appearance. The general structure is sub- concretionary, and true concretions sometimes weather out. The same weathering is sometimes found in the Middle Hogback Sandstone. The Golden Wall Sandstone is often homogeneous and of a bright yellow color in the Uinta region, and often stands as a sheer wall ; hence its name ; but in the Aspen Mountain district these yellow sandstones are broken into strata, and light gray sandstones and shales are intercalated. The ridge like topography characteristic of this group of beds so preva- lent everywhere, renders it easy to trace every outcrop, and the peculiar and persistent characteristics of the upper member greatly facilitate the study of the relation between the Cretaceous below and Tertiary groups above. In the Uinta Mountains the unconformity at this horizon is every- where apparent, The difference in dip is from two to fifteen degrees, and the evidence of intervening erosion is apparent ; but in the Aspen Mountain J 50 GEOGRAPHIC DISTRIBUTION. country the difference of dip is not easily distinguished, but the evidences of erosion are usually apparent. No evidence of unconformity between the Cretaceous formations has been discovered, and the planes of demarkation in many places are not well exhibited. In such a case the lines are drawn on the map only as approxi- mations. Nor is there any evidence of unconformity between the lowest Cretaceous and the highest Jura. Here, also, the stratigraphic plane is sometimes obscure. The teleost shales contain the lowest Cretaceous fossils which have yet been found, and the bad-land beds below the conglomerates contain the highest Jurassic fossils found. The intervening conglomerates I have thought best to call Cretaceous. In a general way the horizon of conglomerates can be easily traced ; still, it is a variable one. Here the sandstones are found with conglom- erates of small pebbles which cannot be easily separated from the sand- stones as they merge into them by imperceptible gradations. Elsewhere well developed conglomerates are found, and sometimes heavy beds of coarse conglomerate prevail. ******* The following section of the Cretaceous Groups was made on the east side of the Green River above Flaming Gorge. POINT OF ROCKS GROUP. Upper Hogback Sandstone. — No. 1, 60 feet. Sandstones ; indurated ; light gray ; stained in patches with iron. No. 2, 60 feet. Sandstones ; gray ; on exposed surfaces stained brown with iron ; containing fragments of coal. No. 3, 25 feet, Sandstones ; very massive ; light gray. No. 4, 5 feet. Carbonaceous shales, with seams of coal. No. 5, 35 feet. Sandstones ; indurated ; gray. No. 6,18 feet. Carbonaceous shales, with seams of coal. No. 7, 80 feet. Sandstones ; indurated ; dark gray. No. 8, 60 feet. Sandstones : massive ; liffht gray. No. 9, 4 feet, Carbonaceous shales, with seams of coal. SECTION OF THE CRETACEOUS GROUPS. 157 No. 10, 110 feet. Sandstones; homogeneous; massive; light gray; indurated. Middle Hogback Sandstone. — No. 11, 275 feet. Sandstone; buff; heavily bedded with intercalated shales and seams of ferruginous clay. No. 12, 75 feet. Friable sandstones and carbonaceous shales. Golden Wall Sandstone. — No. 13, 600 feet. Sandstones ; yellow ; rather massively bedded, Avith intercalated carbonaceous shales. No. 14, 80 feet. Sandstone ; massive ; bright yellow. All the beds of the above group dip to the north about 45 degrees. SALT WELLS GROUP. No. 15, 1,860 feet. Friable sandstones and arenaceous shales. SULPHUR CREEK GROUP. No. 16, 2,000 feet. Dark argillaceous and arenaceous shales. henry's fork group. No. 17, 25 feet. Conglomerates ; pebbles very small, the largest not being more than half an inch in diameter. No. 18, 80 feet. Sandstones; mottled light gray and yellow; showing false stratification. No. 19, 70 feet. Shales; (teleost shales.) No. 20, 135 feet. Sandstones; rather heavily bedded above, but thinly bedded below ; drab. No. 2 I, 40 feet. Sandstones; coarse; buff. No. 22, 100 feet. Sandstones; very friable ; gray, greenish-gray, pink, purple, and chocolate. No. 23, 50 feet. Sandstones ; coarse ; sometimes appearing as a con- glomerate of fine pebbles. No. 24, 100 feet. Sandstones; gray, greenish-gray, pink, purple, and chocolate ; very friable. No. 25, 75 feet. Conglomerate ; dark ; in some places a coarse sand- stone. ******* 158 GEOGRAPHIC DISTRIBUTION. Below I reproduce the section made by Professor Meek on Sulphur Creek to which reference has been made in a previous chapter. I copy his numbers and characterization of the beds, but group them in accordance with the scheme presented in this report. I also invert the order. SECTION OF THE ROCKS EXPOSED ON SULPHUR CREEK, NEAR BEAR RIVER, WYOMING. POINT OF. ROCKS GROUP. No. 1 (28), 200 feet. — Numerous thin seams and layers of dark car- bonaceous shales, with harder thin bands of various colored argillaceous, arenaceous, and calcareous matter, including a few very thin streaks of coal ; the whole being highly charged with vast numbers of fresh and brackish- water shells, such as species of Unio, Corbicula, Corbida, Pyrgulifera, Viri- parus, Meiampus, &c. Dip nearly east, about 75° below the horizon; thick- ness 175 to 200 feet exposed. No. 2. (27). — A long space of perhaps 260 yards or more, with only a few low exposures of light-gray sandstone, showing a slight westward dip. No. 3 (26), 80 feet. — Gray sandstone in place, apparently connected with some masses (that may not be in place) so as to include space enough for 60 to 80 feet, — forms crest of a hill. No. 4 (25), 800 feet. — Brownish and reddish clays with a few distantly separated thin beds and layers of gray sandstone, altogether 750 to 800 feet in thickness. No. 5 (24), 20 feet. — Conglomerate and some red clays. No. 6 (23), 40 feet. — Whitish sandstone — forms crest of hill about 220 to 240 feet in height. No. 7 (22), 110 feet. — Brownish clays and beds of sandstone, the latter light gray below. No. 8 (21), 60 feet. — Brownish clays and sandy layers. No. 9 (20), 40 feet. — Greenish white sandstone. No. 10 (19), 600 feet. — Slope showing above some masses of con- glomerate, like that of division 18, perhaps not in place, with, at places below this, some reddish clays; altogether space enough for 500 to 600 feet in thickness. SULPHER CREEK SECTION, BY PROFESSOR MEEK. 159 No. 11 (18), 40 feet. — Hard gray conglomerate, standing nearly ver- tical, and forming crest of hill about 350 feet high. SALT WELLS GROUP. No. 12 (17), 115 feet. — Brownish and bluish clays, with some beds of white, greenish, and brownish sandstones. No. 13 (16), 45 feet. — Clays and sandstone below, (20 feet), and gray and brown pebbly sandstone above, (25 feet). No. 14 (15), 125 feet. — Bluish laminated clays, with, at top (left or west side), a two-foot layer of sandstone, containing fragments of shells not seen in a condition to be determined. No. 15 (14), 40 feet. — Ferruginous sandstone in thin layers, dipping northwest about 80° below horizon. No. 16 (13). — A valley or depression showing no rocks, perhaps 150 yards across. No. 17 (12), 150 feet. — Light gray sandstones and clays, including a bed of good coal, said to be 7 J feet in thickness; all dipping south-south- east 55° below horizon, and the sandstone above the coal containing many casts, Inoceramus problematicus, with a few casts of Cardium and undeter- mined univalves; altogether showing about 150 feet. No. 18 (11). — Slope and unexposed space, perhaps 200 yards or more across. No. 19 (10), 20 feet. — Light gray sandstone. No. 20 (9), 255 feet. — Gray sandy shales with alternations of sand- stone and clays. No. 21 (8), 95 feet. — Heavy massive bed of light colored sandstone, about 90 feet in thickness, standing nearly vertical, with some 3 to 5 feet of sandy clay between it and the coal of division 7. No. 22 (7), 7 feet 6 inches. — Bed of good coal, said to be 7 J feet in thickness. No, 23 (6), 100 feet. — Greenish and bluish gray sandy clays, with some dark shale at places. No. 24 (5), 100 feet. — Two or three rather heavy beds of light yel- lowish gray sandstone, separated by clays, probably occupying some of the 160 GEOGRAPHIC DISTRIBUTION. space included in division 4. Near the lower part two layers 15 to 18 indies each, of sandstone, containing- Ostrea soleniscus, Trapezium micronema, &c. Altogether 00 to 100 feet or more. No. 25 (4), 300 feet. — Covered space, probably occupied by clays, but showing some sandstone that may or may not be in place; perhaps room enough for 250 to 300 feet. No. 26 (3), 90 feet. — Soft light grayish sandstone, nearly vertical. SUMMIT OF SULPHUR CREEK GROUP. No. 27 (2), 100 feet, — Slope apparently occupied by clays, thickness perhaps 100 feet or more. No. 28 (1 ). — Black shale, only seen in bottom of Sulphur Creek, thick- ness unknown. * * * * * * * BLACK BUTTE QUARTZITE. Southwest of Black Butte Station on the Union Pacific Railroad there is a conspicuous topographic feature known as Black Butte. It is carved from beds of the Point of Rocks Group and is crowned with a dark indurated and exceedingly tough quartzite, which, in the distance, has the appearance of a bed of extravasated material, and even .on closer examination I was deceived by its apparent similarity to some rhyolites. Rocks having a similar appearance and structure are found on the sum- mit of Aspen Mountain, and I unhesitatingly considered the latter to be quartzites; but, on visiting Black Butte, the general weathering and exceed- ingly dark appearance of these beds created the impression that they had been extravasated, though hand specimens had the appearance of quartzite, and I left the field with many doubts as to their nature. -Captain Dutton has since made sections of this rock and examined them under the micro- scope and pronounces it a quartzite. Such a conclusion in connection with the or-eological relations of these beds is very interesting Quartzites, from geological considerations of structure and erosion, are usually supposed to have been at some time deep seated and are often shown to have been involved in profound plication, or TIIE OENOZOIC GEOUPS. 161 implication, and are usually considered to be metamorphosed sandstones, the rnetamorphism due to deep seated agencies; but this quartzite is of very late Cretaceous Age or may even belong to higher unconformable Tertiaries. In either case the same strata on every hand are soft, comparatively frkible, granular sandstones; they are immediately underlaid by great thicknesses of sandstones of like characteristics. They have not been implicated or even plicated. No extravasated material is found in the immediate vicinity to which reference can be made as the origin of crystallization, and these beds on Black Butte are more than 200 feet in thickness, and metamorphism from contact with eruptive rocks, so far as my studies extend in this western coun- try, is exceedingly slight, and indeed such slight change is rarely shown. There is nothing in the surroundings to suggest metamorphism. Is it possible that conditions obtained here favorable to the deposition of silica by chemical precipitation*? This question has been often suggested by facts observed at many other places in the Plateau Province. In my remarks on the Uinta Group I mentioned that some of the sandstones were quasi quartzites, and where such beds of quartzite are found the quartzite structure is invariably local. The same beds traced laterally are typical sandstones; and above and below, soft sandstones and excessively friable shales are found, and there is no local disturbance of these beds. They have simply been displaced in the grand upheaval in common with the sand- stones and shales ; and if this lithologic characteristic is due to conditions of deposition and have not been imposed by the agencies of metamorphism, at what place in the table of sedimentary groups shall we begin to consider quartzites to be products of metamorphism? At Black Butte the quartzite is as high at least as the very summit of the Cretaceous; in the Uinta Mount- ains the quartzites are low down in the Paleozoic series and these are sepa- rated by nearly 30,000 feet of sedimentary accumulations. May we go one foot farther down in the rocks, but across the great gap of unconformity, and say that the Red Creek quartzites were such from original constitution? THE CENOZOIO GROUPS. This description of the geographic distribution of the Cenozoic Groups will be confined to the region north of the Uinta Mountains, except in the 11 P G 1G2 GEOGRAPHIC DISTRIBUTION. case of the Brown's Park Group and the Bishop Mountain Conglomerate. A small strip of country on the south side of the mountains has been given a Tertiary color on the map for the purpose of presenting an interesting- fact in the relation of the groups of that region ; but this is only the border of a broad area through which Cenozoic formations are distributed, and to discuss this border with clearness it is necessary to enter into a consideration of the whole area, which can be done much better when we have the map of that country before us. In the Uinta and White River basins, south of the Uinta Mountains, where these Tertiaries have a great development, the lower formations of this Age have been pretty thoroughly worked out, but there are higher beds not so well understood. I now turn to a consideration of the country north of the Uinta Moun- tains. BITTER CREEK GROUP. Here the Bitter Creek beds have an extensive exposure on the flank of the Uinta upheaval and on either flank of the Aspen Mountain uplift. In the Flaming Gorge district, west of the Green River, the beds of this group rapidly attenuate until they disappear, and here their lithologic character is changed, as the fine grained friable sandstones are replaced by conglomerates ; and as the beds here are dipping at a great angle to the north, so that their upturned edges are well exposed, the harder conglomer- ates are seen to stand in high ledges and w,alls. Eastward from the Green River the beds rapidly thicken until, at Richard's Peak and Quien Hornet Mountain, a section of more than 5,000 feet is presented, and here at the base we have a great development of conglomerates. Richard's Peak itself is a monoclinal ridge of this conglomerate. The disappearance of these beds by attenuation on the west side of the Green River and their increase above the normal thickness east of that stream, together with the change in their lithologic constitution, leads us to infer that we here have the beds exposed near the old shore line that was established by the upheaval of the Uinta Mountain region. Conglomerates are found at the base of the group in many places on the north side of the Uintas, and I suppose the conglomerates on the west side of the Green THE OENOZOIC GROUPS. 168 River to be at the same horizon, namely, at the base of the series, and that the attenuation is due to the non-deposition of the upper beds over the area here brought to light. Of this, conclusive evidence was not obtained, and it may possibly be that these conglomerates represent higher beds which, farther from the shore, were .sandstones of more thoroughly comminuted material. But, while I suggest this possible explanation, I am inclined to consider them as belonging to the lower members of the group, and that after their deposition the area was left as dry land, while the sands were accumulating in the bed of the lake farther from the axis of upheaval. From the Green River eastward, nearly to the foot of Richard's Peak, the base of the group is composed of bad-land sandstones with more indu- rated beds intercalated ; the latter are usually light gray, sometimes quite white ; the former are exceedingly ferruginous and sometimes shaly; but from the western base of Richard's Peak, nearly to the outcrop of the Red Wall limestone, conglomerates are found, and here the whole thickness of the group is much increased. It is interesting to notice that these con- glomerates are found opposite the outcrop of the Red Creek Quartzite. But the materials of which the conglomerates are composed seem not to have been derived from the quartzite, if I may trust my notes : and I should here state that the geographic relation between the quartzite and the con- glomerate did not occur to me while in the field, and. in my notes on the conglomerate I have mentioned that its bowlders are sandstones and lime- stones, and that some of the latter contain Jurassic fossils; but I have recorded observations at only two points — one at Richard's Peak, the other at Bruce Mountain. With the facts now at my command I am inclined to think that when this conglomerate was formed, erosion had not progressed through the Carboniferous groups and Uinta Sandstone so as to reach the quartzite on the upheaved side, but that the conglomerate is composed of sandstones from the Cretaceous groups, and limestones and sandstones of the Jura Trias, and possibly, to some extent, from Carboniferous beds. It would seem that the appearance of the conglomerate here is to be explained by geographic, rather than by geological, considerations — that is, the line of exposure of the base of the group in this region is near to the old shore line ; for it is manifest that here was a headland projecting from the Uinta 164 GEOGRArniC DISTRIBUTION. region into the old Bitter Creek lake, while westward, from Richard's Peak to the Green River, the present exposure of the strata is across the bed of an ancient bay. West from Richard's Peak the plane of separation between the Bitter Creek and Point of Rocks Groups is masked to a greater or less extent on account of the exceeding- friability of the lower beds of Bitter Creek age ; still careful examination reveals the fact that they are unconformable, and this unconformity is very clearly exhibited at the eastern end of the mono- clinal ridge, composed of the Upper Hogback Sandstone of the Point of Rocks Group, near the foot of Richard's Peak, in an amphitheater of erosion at the head of a dry gulch. Between -the western end of the outcrop of Red Wall limestone on the northwest end of the O-wi-yu-kuts Plateau and the Po Canon district the base of the Bitter Creek series is not seen, as it has been carried down bv the fault. On the north side of Diamond Peak the Bitter Creek beds are lying horizontal, and, studying this mountain from that side, it would seem to be composed of Bitter Creek beds, perhaps capped by beds of the Lower Green River, but on climbing the mountain its summit is seen to be composed of angular fragments of sandstones piled in an indiscriminate maimer, the age of which was not fully determined ; descending it on the south side tlys same confusion is observed. Of what the principal mass of this peak is composed I do not know. In the Po Canon district along the channel of Vermilion Creek and many of its lateral tributaries, deep corrasion has produced many steep escarpments of the Bitter Creek beds. Here we find the Point of Rocks Group standingon edge, and near by, and separated from the former only by narrow gulches, Bitter Creek beds of a horizon about midwa}^ in the group are found lying hoiizontally; but in a few places lower beds of the Bitter Creek series are turned up on edge with the Point of Rocks beds and the middle beds of the Bitter Creek Group lie over their upturned and eroded edges unconformably, and over some of the upper beds of the Point of Rocks Group in like manner. Thus the middle beds of the Bitter Creek overlap the lower beds, not because they were deposited over a broader area, but because the lower beds in a part of their extent were exposed to erosion and THE CENOZOIC GKOUPS. 165 carried away prior to the deposition of the middle beds. These facts are illustrated in Fig. 15. I do not think that the base of the Bitter Creek series is found exposed in this vicinity. The displacement here has evidently been exceedingly complex, and its study is rendered difficult by unconformities, and it is not always easy to determine to which class of agencies certain O 500 nui urn inii — 1000 1SOO /* North B. C. Bitter Creek Group. P. R. Point of Rocks Group. Fig. 15. phenomena are due. In some portions of the line of displacement the beds are marked by certain late Tertiaries of Brown's Park age as will be more fully explained hereafter. West of Bishop Mountain, stretching across the many tributaries of the Vermilion, there is a broad expanse of country where the beds of this age are exposed in naked bad-land hills, and on either flank of the Aspen Mount- ain uplift they are seen usually forming regions sterile and desolate. At the head of Little Bitter Creek there is a stretch of table land where beds of Bishop Mountain Conglomerate are found. In the late redistribu- tion of this conglomerate its materials have been carried quite over the line separating the Bitter Creek from the Point of Rocks Group, so that the junction is completely masked, but in the escarpment south of the plateau which faces Quien Hornet Mountain the junction is well revealed ; and the same is true farther to the north in, lateral canons along the upper course of Little Bitter Creek. The conglomerates found at the base of the series on the flank of the Uh}tas are not seen on the flanks of the Aspen Mountain uplift, and the Bitter Creek beds attenuate toward the north. From these facts I infer that the materials of the Bitter Creek Group were derived in large part at least from the Uinta region, that is that the bad-land rocks of Mesozoic Age were earned from the Uinta region and redistributed as bad-land beds of the Bitter Creek period. In this great fresh water basin conditions favorable to the deposition of 166 GEOGRAPHIC DISTRIBUTION. carbonaceous shales and lignitic coal obtained from time to time, now here now there, and such shales and coals are found distributed in great profu- sion throughout the entire area which has been studied. In a section made on the south side of the railroad between Lawrence Section House and Rock Springs more than 30 seams and beds of coal are noted. The coals of this horizon in the vicinity of Black Butte Station have been frequently described by other geologists. It is not my purpose to discuss the distribution and character of the lignitic coals in this report. LOWER GREEN RIVER GROUP. In the Flaming Gorge district the Lower Green River Group overlaps the Bitter Creek Group, and farther westward disappears by attenuation. The course of the Green River from the northern border of the area embraced on the map to the hogback six miles north of Flaming Gorge is through the beds of this group, and an irregular escarpment of these beds having deep reentrant angles, and spaces broken into low hills, faces the axis of the Aspen Mountain uplift. The escarpment known as Pine Bluffs on the east side of the uplift is of this age. Another outcrop is found north of Dry Mountains and west of the Po Canon district, where their upturned edges are exposed on the border of a basin of displacement or sag due to a downthrow. This group is composed chiefly of bituminous shales and impure lime- stones, the latter being both arenaceous and argillaceous; but to the south, near the Uinta uplift, the group is much thickened and the shales are replaced by sandstones, and conglomerates of fine pebbles appear. From this fact it is inferred that the beds of this group are derived from the Uinta region, and that the material was supplied from limestones and sandstones of Carboniferous Age. Conditions favorable to the accumula- tion of Carbonaceous shales and lignitic coal are less frequent than in the former period, but a fine bed of coal has been found at the base of this group on the bank of the Green River, about eight miles below the station, and Carbonaceous shales and thin seams of coal have been found at other hori- zons elsewhere. THE CENOZOIO GROUPS. 167 UPPER GREEN RIVER GROUP. The beds of this group are well exposed in high escarpments on either side of the Green River from the northern boundary of the district embraced on the map nearly to the hogback six miles above Flaming Gorge, and they stretch in a continuous but irregular belt on the west side of that stream for the same distance, and are exposed on Henry's Fork for many miles. On the east side of the Green River they are found in outlying discon- nected patches. The most important of the latter are colored on the map. They are also seen in the district east of Po Canon with their edges upturned around the basin of displacement previously mentioned. It is probable that these beds are also found east of Pine Bluffe, but when that country was studied in 1868, I had not separated the Upper from the Lower Green River beds, and not having visited the country since, I am not prepared to give any facts concerning the matter. In a former 'chapter I stated that the Upper Green River beds were, interpolated between Bridger and Lower Green River only through a por- tion of the great Tertiary basin north of the Uinta Mountains. These beds have their greatest development in the region about Green River Station, extending for 20 or 30 miles to the north and south, and it is probable that the material of which they are composed was derived in part, at least, from other than the Uinta region, though doubtless this region yielded a share of the detrital matter. Carbonaceous shales and lignitic coal are found at this horizon on Henry's Fork. Two of the coal beds have been explored and when tested are said to have yielded fair coals. I have already in a former chapter described the Tower Sandstone at the base of this group, and explained the nature of ihe unconformity between the Upper and Lower Green River Groups. BRIDGER GROUP. The Bridger beds are found outcropping on the western border of the district under discussion north of Henry's Fork, and again to the east of the Po Canon district in the sag of displacement north of the Dry Mountains. No unconformity has been discovered between the Bridger and Upper 168 GEOGBAPHIC DISTEIBUTION. Green River, and the plane of demarkation is obscure, or rather there is no plane of demarkation, but the separation is transitional ; but the bad-land beds of the Bridger Group are very distinct from the limestones and sand- stones of the Upper Green River. In the latter, sandstones usually rather massive, and in the case of the Tower Sandstone greatly so, have impure limestones intercalated. In the former, bad-land sandstones prevail, and these are largely green sands, but irregular beds and aggregations of chalcedony are abundant, and high in the series two well marked and persistent lime- stones are found. These beds of chalcedony afford the moss agates for which the region about Fort Bridger has been noted. I suppose them to have been deposited by chemical precipitation from waters highly charged with silica. The limestones are in many places crypto-crystalline, and break with a conchoidal fracture and often have the ring of phonolite. I consider these also to be chemical precipitates. Fresh water fossils are sometimes found imbedded in the crystalline masses, but can rarely be obtained in a perfect state, but fossils are more abundant in the arenaceous and argilla- ceous partings, and can be obtained in a good state of preservation. In the green sands vertebrate fossils have been found in abundance, and concern- ing them much has already been written by eminent paleontologists. No coal has been discovered in the Bridger Group. brown's park group. These beds are found in the valley known as Brown's Park and a dis- trict of country stretching thence to the southwest beyond the Snake and Yampa Rivers. In Brown's Park they lie in a deep basin of erosion, the bottom and sides of which are composed of Uinta Sandstone. This basin is in the very axis of the Uinta uplift. Eastward, both on the north and south sides of the area of outcrop, the beds are seen to rest unconformably upon all of the Carboniferous, Mesozoic, and Cenozoic formations previously mentioned. Its unconformity with the Upper Green River, Lower Green River, and Bridger beds is well exhibited in the Dry Mountains in many fine exposures. Its structural relations to these beds will be discussed here- after. Its sandstones are bad-land rocks of exceedingly fine texture. In THE CENOZOIC GKOUPS. 169 some places these rocks are composed of thin laminae of many delicate colors, but they do not readily part along the planes of stratification, but crumble easily and often break in large masses. Extensive beds and irregu- lar aggregations of chalcedony are found and I suppose them to have been deposited by precipitation. Conglomerates are found, at the base, in some localities having a great development. The beds incline slightly from the wall of the park on the south side ; this inclination may be due to the bottom on which they were deposited. On the north side the beds are turned up at a great angle, showing much displacement since they were deposited, and immediately outside of the irregular line of outcrop a fault has been observed with its throw to the south. In Brown's Park the streams which come down from the mountains on either side have in many places cut through these beds and reveal in the depths of their channels the old floor of Uinta Sandstone. But a few hun- dred feet of these beds are left in Brown's Park, but eastward a much greater thickness remains preserved from denudation. It is probable also that this greater thickness is due in part to greater sedimentation. In the northeast portion of the Po Canon district there is another out- crop Of this group. Here the beds rest unconformably on the Uinta Sand- stone, the several Carboniferous groups, the several Mesozoic groups, on Bitter Creek beds, and also on the heterogeneous mass of sandstones of which Diamond Peak is composed. BISHOP MOUNTAIN CONGLOMERATE. This conglomerate is found only in isolated patches as remnants adven- titiously preserved from the general erosion to which this widely spread formation has been subjected. An outlying patch or fragment is found on the north side of Sage Creek overlying unconformably the beds of' Lower Green River age. Another is found on the plateau where Sage, Little Bitter, and Pretty Creeks have their sources; here the conglomerate rests on Point of Rocks beds. Another is found on the summit of Quien Hornet Mountain resting on Lower Green River beds. Another is found on Bishop Mountain resting on Bitter Creek . beds. On the south side of the Uinta Mountains a fragment is found west 170 GEOGRAPHIC DISTRIBUTION. of Echo Park resting- on Carboniferous beds. Another fragment is found ten or twelve miles west of the Canon of Lodore resting on Carboniferous and Jura Trias beds. A fragment is found west of Brush Creek also lying on the Car- boniferous and Jura Trias beds ; and the Wa-ka-ri-chits are capped with this conglomerate, which here rests on Sulphur Creek beds. These are the only fragments which I have discovered in the area em- braced on the map, but to the westward, on both flanks of the Uinta uplift, this formation has a much more extensive geographic development and it is also found in greater thickness. On the north side of Connor Basin, at the head of Sheep Creek, this conglomerate has a thickness of more than a thou- sand feet. » There are some conglomerates on the peaks of the Dry Mountains which at one time I believed to belong to this period, but I now think they are of the Brown's Park age. In the destruction and redistribution of this formation, the materials of which it was composed have been scattered in many places here and there on either flank of the Uinta uplift. The conglomerate is composed of bowl- ders and pebbles of sandstone, quartzite and crystalline schists, but sand- stones and quasi quartzites probably of the Uinta period greatly prevail; but in the original beds and redistributed materials found so abundant north and northeast of Mount Wheeler where the Red Creek Quartzite is exposed, white quartz and crystalline schists are far more abundant than elsewhere. Sometimes at least the cement is calcareous. In the fragment west of Echo Park large and somewhat angular blocks of Uinta Sandstone are found. I think that many geologists would ascribe this conglomerate to the action of ice, but throughout all that portion of the Rocky Mountain region which I have studied, I have so frequently found gravels and conglomer- ates of sub-aerial origin, and have in so many cases found reason to change my opinion concerning them, often having attributed a drift like deposit to glacial action, and afterward on further study abandoned the theory, being able to demonstrate its sub-aerial origin, and witnessing on every hand the accumulation of such gravels in valleys and over plains where mountains rise to higher altitudes on either side, and having in many cases actually seen the cliffs breaking down and the gravels rolling out on the floods of a THE CENOZOIC GROUPS. 171 storin, I am not willing- to disregard explanations so obvious and so certain for an extraordinary and more violent hypothesis. Irregular accumulations of clay, accumulations of sand, of gravels, and bowlders having in a general way all the lithologic characteristics of " drift" are very common in the Rocky Mountain region, and in many cases I am convinced that their origin can be traced to ordinary atmospheric agencies acting- on the adjacent hills and mountains; and no glaciers or icebergs are needed for their explanation. Nor need the thickness and extent of this Bishop Mountain Conglomer- ate serve to weaken this explanation, for the sub-aerial gravels in the valleys between the ranges in the Basin Province are of equal and often of greater development. Whenever a low plain, valley or basin is for a comparatively long period but little elevated above the base level of erosion, and during this time mountains and hills stand about the lowlands, there must be a great accumulation of drift, and where the highlands are areas of progressive ele- vation and the lowlands areas of progressive subsidence this accumulation may continue indefinitely. Thus it is that I attribute the drift of the Rocky Mountain region to sub-aerial ag-encies, chiefly the action of rains and streams. Mountains are not degraded by the slow washing down of their surfaces Jbut they are dug down by the corrasion of deep channels and the undermining of ledges and cliffs ; and the materials thus loosened from the great rock masses to which they originally belonged are carried down to the lowlands by storms. In one hour of storm more material is carried to the lowlands than in days, weeks, or months when the mountain streams are clear brooks. Yet there has been glacial action in the Uinta Mountains, for there are found undoubted MORAINAL DEPOSITS. The deep valleys that lie at the feet of the axial peaks of this great range have been beds of now extinct glaciers. Morainal deposits, roclies moutonnees, glaciated grooves, and morainal lakelets are found in very many of these elevated valleys. Often the valleys are so choked with the materials thus accumulated by the action of ice that travel across them is of great difficulty. From the crevices between these ice piled rocks high pines 172 GEOGRAPHIC DISTRIBUTION. and firs are growing, and hundreds, thousands of little basins filled with clear, cold water are found. These glacial deposits are doubtless of much later origin than the Bishop Mountain Conglomerate; often they are min- gled with and masked by drift which has been brought down from the heights by storms, and in many places it is impossible to separate that which is due to this latter agency from that which is due to the agency of ice ; and as you descend the valleys away from the peaks where the glacial snow was accumulated the mingling of the two increases by an increase in the amount of drift until at last the glacial formation is lost and drift only appears; taken throughout the Uinta Mountains, the glacial material is far less in quantity than the drift material. What I have thus described as glacial action is exceptional or local and trivial as compared with drift agencies, "which must always obtain in mountain regions alike when they are free from glaciers or when the elevated valleys are filled with ice. Thus the glacial epoch in the Uinta Mountains was doubtless a reality; the evidences of such a time are abundant, but they are found only high up on the range, and the gravels and bowlders of the lowlands attest only to the ordinary action of drift agencies. I may remark here that the evidences of the same glacial epoch are abundant in the Park Mountains; but there also the glaciers were confined to the elevated ranges. The gravel beds on the lowlands are true drift. LIGNITIC COAL. But little reference has been made to the lignitic coals found in the Uinta region; it is expected that the coals of the Plateau Province will be discussed in a separate volume. OHAPTEE V. STRUCTURAL GEOLOGY. In the preceding" chapters many of the facts relating- to the structural geology of the region under discussion have been presented, but they were given only to serve purposes relating to the subjects of which I was then treating. In the first chapter it was necessary to refer to this region in characterizing the three provinces ; in the second, other facts were presented in explanation of the grouping of the sedimentary rocks ; and in the fourth, still other facts were given in discussing geographic distribution. I now pro- pose to assemble these facts with others relating to structural geology, for the purpose of more clearly setting forth the geological structure of the Uinta Mountains, Yampa Plateau, Junction Mountain, Diamond Peak, the Dry Mountains, Brown's Park, and the Aspen Mountain district in the order thus indicated. DESCRIPTION OF ILLUSTRATIONS. For the purpose of more clearly setting forth these facts certain illus- trations have been prepared and will be found in the atlas. Structure Sections. — On Plate I is grouped a series of sections through the Uinta Mountains, from south to north, and six miles apart. In each section the structure observed has been projected below the line of sight to the level of the sea, that the facts observed might be represented in a more graphic manner. This hypothetic projection represents the most prob- able condition of underground structure to that depth, yet there may be unconformities unknown to us and of which no hint is given in the stra- tigraphy at the surface or in the structural geology of the surrounding country ; but from the absence of these indications, such unconformities are rendered improbable. As the Uinta upheaval began at the close of the Point of Rocks period, 173 174 STRUCTURAL GEOLOGY. this gives us a datum point from which to measure displacement, degrada- tion in the region of uplift, and sedimentation in the region of downthrow. For this reason the group is graphically accented in each section. Displacement Diagrams. — On Plate II is grouped a series of diagrams designed to represent displacement and degradation. Each diagram corre- sponds to and is derived from a section in Plate I, and is composed of three lines: the sea level line and the surface line, which are the same as those in the corresponding section, and a third, a displacement line, which is the accented line of the section, projected in the region of uplift from the observed outcrop of the group which it represents (Point of Rocks Group), to the position it would have in the section had there been no degradation but displacement only. We thus take the sea level as the zero from which to measure displace- ment; and by introducing the surface line, the accented line above becomes a zero for the measurement of degradation in the region of uplift; and as this accented line represents the position of the last bed deposited prior to the inception of the upheaval (which is the highest Cretaceous bed), it also forms a zero line from which to measure the sedimentation on the flanks of the upheaval which occurred subsequent to the inception of the displace- ment; or, in other words, a zero line from which to measure Post-Cretaceous sedimentation. Hence in the region of downthrow, with the accented line as the zero, the surface line measures the amount of Post-Cretaceous sedi- mentation, minus an unknown loss by degradation. It may be well here to explain the method by which the position of the displacement line was determined. In the topographic survey the altitude of many points on the surface is fixed with a reasonable approximation to accuracy by the use of the barometer and theodolite. These points are the junction of drainage lines, the summits of peaks, and many other salient and conspicuous topographic features ; and from these, contour lines are drawn by inspection. Hence the topographic map fixes the position of any bed appearing on the surface with all the accuracy necessary for the scale on which these sections and diagrams are drawn. Another factor used is the general thickness of the beds. This is deter- mined by measuring them where they outcrop on the flanks of the uplift. DESCRIPTION OF ILLUSTRATIONS. 175 The surface lines, the outcrop of the beds along these lines, and the thick- ness of the beds are factors sufficient for the construction of the sections and diagrams, but the observed dips and strikes afford many valuable checks in their construction. A single diagram represents displacement and degradation in two dimen- sions; that is, in a vertical plane from south to north across the axis of up- heaval. A group of these diagrams constructed on parallel planes, separated by equal intervals, and having the scale of these intervals in the group the same as the vertical and horizontal scale of each diagram, serves to repre- sent displacement and degradation in three dimensions. Stereogram. — To more fully bring the displacement into visual compre- hension, the stereogram, Plate III, has been constructed. Here the lines representing the level of the sea, and those representing the present surface are omitted, leaving only the displacement lines; and between these others have been interpolated, so that the intervals are but 3,500 feet; and this has the effect of projecting the region in relief, as it would appear in a bird's-eye view had there been displacement but no degradation. To fully compre- hend the meaning of this stereogram, it is necessary to remember that every deviation of a line from horizontality represents a corresponding inclination of the beds, and careful inspection will show that absolute horizontality very rarely occurs. The stereogram fails to represent the abruptness of flexure in some places, as the lines of displacement show the intersection of vertical parallel planes with the summit of the reproduced bed, and these planes have a north and south direction. Wherever thev do not cross a flexure in the direction of the dip, but to a greater or less extent oblique to it, to such extent do the displacement lines fail to represent the abruptness of the flexure or angle of dip ; in other words, the stereogram does not fully represent dis- placement in an east and west direction. But the axis of flexure in the Uinta Mountains has an easterly and westerly direction, and all other displace- ments are subsidiary to this ; and as the displacement lines are drawn trans- verse to this axis, the general characteristics are well represented. It fails also to give the relation of the displacement to the level of the sea except in the case of the first line in the foreground. I am indebted to Mr. Gilbert for this method of illustration. 17G STRUCTURAL GEOLOGY. It will be shown hereafter that pari passu with upheaval, degradation progressed, and with downthrow, sedimentation, and it is probable that degradation and sedimentation were necessary to upheaval and downthrow. Yet, for certain purposes, it is desirable that displacement be considered in- dependent of the degradation with which in nature it must always be more or less complicated, and hence the stereogram has been constructed. Bird's-HJye View. — The difference between upheaval and degradation in the region of uplift can be determined by examining the diagrams in Plate II; but to give a more graphic representation of this important fact in the Uinta uplift, the bird's-eye view, Plate IV, has been constructed. Other sections, diagrams and stereograms are found in the atlas, to which reference will be made in appropriate place. All of these sections, diagrams and stereograms are constructed on symmetrical scales ; that is, vertical and horizontal scales are the same and all agree with the map. THE EASTERN PORTION OF THE UINTA MOUNTAINS. DISPLACEMENT. The Uinta Mountains have been produced by the degradation of a great upheaved block having its axis in an east and west direction. This axis is not a straight line ; in that portion of the range under discussion it makes a great curve to the north; on the western border of the district the axis is found at Leidy's Peak. It runs a little north of Mount Lena, and in Brown's Park it passes about two miles north of Swallow Canon, then it deflects southward and is found again On Vermilion Creek about four miles above its mouth. The total upheaval above the sea level, along its axial line, is about 30,000 feet. The method by which the amount of uplift is ascer- tained is as follows: It is in evidence that the upheaval began at the close of the Point of Rocks period. The thickness of the rocks exposed on both flanks of the uplift below that horizon is a little more than 25,000 feet, and the lowest bed seen is 5,400 feet above the level of the sea. The Uinta Sandstone has not been lifted as high at Leidy's Peak as it has at the mouth of the Vermilion by about 2,000 feet, but the Mesozoic groups attenuate from east to west, in the same distance, something more than 2,000 feet, and DISPLACEMENT. 177 hence the summit of the Point of Rocks Group was earned about as high in the western as in the eastern region. From the axis on either side the beds are flexed in a gentle curve to the north and south for many miles until the flanks of the range are reached, where the beds are seen to drop down by abrupt flexures or faults, and these lines of maximum displacement are subparallel with the axis. Thus a great block having its longest axis in an easterly and westerly direction was uplifted. In some places this block was severed from the adjacent country by fracture ; in some places by more or less abrupt flexure; and it was itself flexed gently from the axis either way. Nothing more is needed to explain the character of this uplift between the lines of maximum dis- placement, but the latter present many interesting facts. On Plate III, this portion of the Uinta uplift, together with the dis- placements of the Yampa district are represented in a stereogram. The general axis of the great uplift is easily recognizable, as is also the gentle flexure in either direction from this axis. Then the great Uinta fault h, h, h, h is seen on the north with the Flaming Gorge branch i, i. On the south side of the Uinta Mountains in the Island Park district we find the north Ti-ra-kav flexure h, k, k and the south Ti-ra-kav flexure I, I, I. In the Yampa district on its northern border the eastern extension of the north Ti-ra-kav flexure is scarcely seen, as there is an oblique area of upheaval between the Island Park sag d, d and the Echo Park sag e. The flexure of the Echo Park sag also becomes less abrupt in an easterly direction until it almost fades out. The displacements south of the Island Park and Echo Park sags need no further mention here, as they will be discussed in a sub- sequent portion of this chapter. It will be seen in the Island Park district on the south side of the Uinta uplift that there are two lines of maximum downthrow approxi- mately parallel, the north and south Ti-ra-kav flexures ; the beds between these two flexures are nowhere horizontal. The south Ti-ra-kav flexure disappears toward the west until the region. embraced in the stereogram is passed ; a little farther westward it re-appears, sometimes as a flexure but usually as a fault. Passing the oblique uplift between the Island Park and Echo Park sags we again have two lines of maximum downthrow. The 12 p G 178 STRUCTURAL GEOLOGY. more northern, which is a continuation of the northern Ti-ra-kav flexure, is but faintly seen in the stereogram ; the southern, which is the flexure of the Island Park sag, is more pronounced. All of these maximum flexures on the south side appear to be but slight from an examination of the stereo- gram, as its scale is very small and no exaggeration has been permitted ; but they are very important characteristics in the structural geology of the region, and give rise to very remarkable topographic features. In the broad generalization necessitated by the scale of the illustration many minute displacements, parallel, oblique and transverse to these larger, dis- appear ; that is, in the production of these greater flexures the beds were locally contorted and broken. Turning now to the north side of the Uinta uplift, we find that the line of maximum displacement, beginning at the eastern extremity, is at first a gentle flexure with comparatively small uplift; but the flexure rapidly increases in abruptness and magnitude until at last we find that the beds are broken and we have a fault ; but only a portion of the uplift is by faulting, and the beds on the thrown side are turned up at the edge. Farther west- ward the beds below lie nearly horizontal, and the beds on the upheaved side are flexed downward; and these conditions alternate so that we some- times have the upheaved beds flexed downward only, while the thrown beds are nearly or quite horizontal. Again, we have the upheaved beds nearly horizontal at the edge and the thrown beds decidedly flexed upward; and another variation is found where the upheaved beds are flexed downward and the thrown beds upward. It is probable that the displacement began by flexure, and continued until much of it was made in this way, and finally the beds broke, and the latter part of the displacement was by faulting. And when this faulting occurred, in some places the beds broke on the side of the flexure nearer the axis, in other places on the side of the flexure farther from the axis, and in still other places between the sides of the flexure; that is, the line of fracture meanders along the zone of flexure. As we approach the Flaming Gorge district we find that the faulting is greatly diminished, while the flexing is increased, the total throw or uplift, as we may please to consider it, remaining approximately the same. At last this line of abrupt displacement branches, DISPLACEMENT. 179 and we have a faulted flexure to the south and an abrupt flexure to the north; the southern branch, farther westward, becomes a simple flexure, and the northern branch changes its course somewhat, so that the beds are greatly warped; then it becomes a faulted flexure, and finally a clean fault. Thus the great Uinta block was uplifted, behaving in part as an integer to the extent that it was separated by flexure and fracture from the adjacent country, and as a body of minute parts as it was flexed along the axial line. We are interested to know at what rate this great uplift progressed. The evidence bearing on this point is of three classes: first, that derived from the character of the displacement itself; second, that derived from degradation; and third, that derived from sedimentation. The displacement is partly by faulting, partly by flexing. A priori, it would appear that whether any given displacement should be by faulting or flexing would be determined by four conditions, severally or conjointly: first, rate of displacement; second, constitution of the beds displaced, flexi- ble and brittle beds being contrasted; third, the depth of the beds consid- ered, for the deeply seated beds, being less free to move, would be more liable to bend, and beds nearer the surface, being more free to move, more liable to break; and fourth, the nature or application of the force producing displacement. Observed facts show that two at least of these a priori condi- tions, the second and third, are true conditions. Both Mr. Gilbert and myself have observed in the transverse section of a displacement that the hard beds have been broken and the soft beds bent, and I have elsewhere published such a section. In a region of country visited by Mr. Gilbert during the past season, he found that the displacement in one district was by faulting, and in an- other by flexing. In the region of faulting there had been but little sub- sequent degradation ; in the region of flexing, much subsequent degrada- tion; and these conditions led Mr. Gilbert to the conclusion that the depth of the beds below the general surface at the time of the displacement had determined these characteristics, and in studying facts which had been collected in other regions by myself, he was able to show that they also lead to the same conclusions.. The places where these facts were observed are so widely spread throughout the Plateau Province that it will not be 180 STRUCTURAL GEOLOGY. convenient to assemble them here, but I am strongly disposed to accept Mr. Gilbert's conclusions. The fourth condition is supposable, but that it is a vera causa I cannot say. I have often supposed it to be such in the study of particular faults, but on further study it has eluded my apprehension. We sometimes find a displacement of many thousand feet where the uplifted region is separated from the thrown by a broad zone of gently dipping beds, and it would seem a priori that where two regions were thus separated, the zone of change would be by flexure rather than by a series of ruptures, and such is usually though not invariably the case, and this seems to be a question of application of force, or in other words, character of strain, and it cannot be doubted that such a condition must be taken into consideration. Mr. Gilbert evidently recognizes it as a true cause, for in discussing the Basin Ranges, he says: " The displacement of comparatively rigid bodies of strata by vertical or nearly vertical faults, involves little hor- izontal diminution, and suggests the application of vertical pressure from below." As to the first cause, rate of displacement, it is manifest that accelera- tion promotes rupture, retardation, flexure; but the other conditions which I have set forth so modify this rule, that rate of displacement cannot with any certainty be determined from facts of flexure and rupture alone. The Uinta upheaval was partly by flexing, partly by faulting, and if there were no other conditions to determine these characteristics, we might say that so far as the beds were flexed they give evidence of slow move- ment ; and so far as they were ruptured, evidence of a more rapid move- ment; and the twenty-five or thirty thousand feet of beds which are exposed to view and were involved in this uplift were chiefly of a character quite brittle, and this increases the evidence in favor of slow upheaval by flexing ; but flexing may have been at great depths, and the superincumbent masses produced a condition favorable to flexing even in a rapid rate of movement. Many substances, especially metallic, are known to flow under great pressure, and it is probable that great pressure would produce in all rocks a quasi-fluid condition, and hence we cannot say that flexing attests to a slow rate. On the other hand, faulting, without considering other con- DEGRADATION. 181 ditions, would seem to attest to rapid rate, but the character of the strain may have determined the rupture. Hence we may conclude that the characteristics of the displacement do not afford satisfactory evidence of the rate of its movement. It will be seen hereafter that facts relating to degradation and sedimen- tation do give some satisfactory conclusions. DEGRADATION. EXTENT OF DEGRADATION. The area of degradation which I have often for convenience called the region of uplift, represented in Plate II, embraces a little more than 2,800 square miles. From this about 8,300 cubic miles of rock have been carried away by rains and rivers — a mean degradation of about three cubic miles to the square mile. But a part of the region embraced on that plate will be discussed hereafter under the head of Yampa Plateau, and in what I have said concerning the Uinta Mountains above, this region has not been considered. Taking the Uinta Mountain region proper, then, we have an area of about 2,000 square miles from which about 7,100 cubic miles of rock have been taken, giving a mean degradation of 3£ cubic miles to every square mile of surface. But this has not been taken from all points equally ; a greater amount has been carried from the axial region than from the districts along the flanks ; and in the axial region a greater amount has been taken from the eastern than from the western end. Here where the displacement lines are carried highest, the surface lines are lowest, so that the degradation is more, not only by the amount of greater uplift but also by an additional amount in the deeper excavation of the valley. The region of highest uplift is the region of lowest degradation, and here more than 25,000 feet of beds have been removed. To more fully comprehend the amount of degradation and its relation to upheaval, the bird's-eye view, Plate IV, has been constructed. Here we have represented a block from the Uinta Mountains forty miles in a north and south, and fifty miles in an east and west, direction. The one-half of the view in the foreground represents the degraded region, and the one -half 182 STUCTURAL GEOLOGY. in the background as it would appear had there been no degradation, but uplift only. It is believed that a careful study of the illustration will be amply repaid. RATE OF DEGRADATION. It would be interesting to know at what rate this degradation has pro- gressed. We know of no means by which an absolute rate can be deter- mined, but there are certain facts which lead to the conclusion that a maximum rate for this region was never established. These facts are found in the character of the topographic features produced by degradation, but in order that we may more fully understand them it will be well to briefly examine the agencies, methods, and conditions of degradation. Degradation consists of disintegration and transportation, and they are mutually dependent parts of the general process. If disintegration is re- tarded, transportation is retarded, for the materials must be furnished ready for transportation. Again, if transportation is retarded, disintegration is re- tarded, as the beds to be disintegrated are to some extent protected by the accumulated products of the process; and if either is accelerated, the other must be accelerated. DISINTEGRATION. The rock masses which are brought above the level of the sea by up- heaval are always found to be more or less coherent. Although these rocks are chiefly of sedimentary origin, the exceptions being extravasated masses, still they are usually found to have assumed a more or less crystalline struc- ture, due either to the manner of their deposition or subsequent metamor- phism, so that the minute parts, molecular or mechanical, of which these rocks were originally aggregated, cohere in great masses. There are many degrees of this coherence from bad-land sandstones or shales of extreme friability to schists and granites of extreme coherence ; but whatever may be their degree of coherence, they must be disintegrated prior to their transportation to the sea. PETROLOGY AS RELATED TO DISINTEGRATION. The endurance of rocks as determined by their coherence depends on— 1. Geologic Structure. — The rocks may be irregularly massed or strati- DEGRADATION. 183 tied; the latter yield more readily than the former. The strata may be thick or thin; the latter yield more readily than the former. The strata may be horizontal or inclined, and the latter yield more readily than the former; and in each condition above mentioned heterogeneity promotes disinte- gration. 2. Lithologic Structure. — Under this head we may consider whether the beds are compacted crystals or cemented sediments; the latter yield more readily than the former, and heterogeneity promotes disintegration. Both in detrital and crystalline rocks there are certain conditions which may be grouped under the head of induration, including hardness and toughness, and the greater the induration the greater the stability; and the law of hetero- geneity applies also to this condition. 3. Chemical Structure. — The principal condition of chemical constitu- tion relating to endurance is solubility; the soluble yield more readily than the insoluble, and in chemical constitution the homogeneous is more stable than the heterogeneous. It will thus be seen that in each particular mentioned above, the homo- geneous is more stable than the heterogeneous, and these particulars in their correlations are themselves conditions of heterogeneity, so that the whole subject of petrology in its relation to disintegration, is one of degree of heterogeneity. DYNAMICS OF DISINTEGRATION. The principal forces of disintegration are gravity, heat, crystallization and chemical reaction. Gravity disintegrates the rocks directly where they break from cliffs and ledges partly by their own weight, and are further dis- integrated by the fall, and indirectly through the agency of water in abra- sion. Heat disintegrates the rocks by change of temperature, and probably by expansion of water permeating the rocks. Crystallogenic force also acts through the agency of water, for where the water which has permeated the rocks is frozen, the expansion due to this crystallization breaks them asun- der. In chemical reaction the rocks are broken up through the agency of water which acts directly in dissolving them, or indirectly in promoting other chemical reactions. 184 STRUCTURAL GEOLOGY. In disintegration, therefore, we have ah intricate plexus of forces acting on an intricate plexus of matter. Now, so far as disintegration depends on the forces of heat, crystalli- zation, and chemical change, the climate of the region is involved, aridity being contrasted with humidity, heat with cold, and great changes in either factor of climate promote disintegration ; and so far as disintegration de- pends on gravity, the declivity of the surface exposed to degradation is in- volved, and a breaking np of the general declivity into greater and lesser slopes, promotes disintegration. We may, therefore, discuss the dynamics of disintegration as conditions of climate and declivity, and hence we may consider the factors of disintegration to be petrology, climate and declivity, and affirm that if the rate of transportation is sufficient to allow the forces of disintegration to act to their fullest extent, the rate of disintegration will depend on the heterogeneity of the rocks, heterogeneity of climate, and heterogeneity of declivity. V TRANSPORTATION. Gravity is the force acting in transportation. It acts directly in trans- porting masses which fall from ledges and cliffs, and indirectly through the agency of water. In this indirect method there are two sources for the mechanical motion involved in. the process: the one is the force of gravity inhering in the water, which is the vehicle of transportation, the other the force of gravity inhering in the rocks transported. Let us call the latter rock power, the former water power, and the rock material transported, load. It is manifest that if the rocks on disintegration were in a fluid state, their own gravity would transport them. All of the rock material which is dissolved is placed in this condition, and its own gravity is the force which transports it; it does not float on the water, but behaves as an integral part of it, and with it obeys the laws of hydrodynamics. In this case the water is not the agent of transportation, but onl}' the agent of disintegration. When the rocks are disintegrated mechanically the water is properly the vehicle of transportation, and we have two cases, the one in which the load is driven by the water, the other in which it is floated on the water. When the transported matter is driven by the water along the bottom of the DEGRADATION. 185 channel, both rock power and water power are employed, these two forces acting in inverse ratio with the specific gravity of water and load; that is, less water power is needed to drive the rock by the amount of the weight of the water displaced by the rock, for to this extent, rock power is used. The amount of load which may be transported by the driving process, or in other words, by water power, plus an amount of rock power, begins with that degree of comminution which permits the load to be moved, and is limited by the power of the water on one hand and by friction on the other. And wherever the degree of comminution is such that the matter is transported partly or wholly by the agency of flotation to such extent as flotation is employed, the driving ceases and other limits are imposed. We come now to the principal method of transportation ; that is, that by flotation. Here the rock power is used in transportation, and the water is the vehicle. If the matter to be floated is of the same or less specific gravity than the water, a condition seldom obtaining, flotation is perfect, and the water power is not used either in transportation or to pro- mote flotation. But when the floating matter is of greater specific gravity than the water, then the water power is used in promoting flotation. With a given amount of water and sufficient supply of load, the extent to which the water power will be utilized in promoting flotation will depend on two conditions : First, the power of the water, which is measured by fall into mass, or which may be expressed as velocity or again as declivity ; second, it will depend on the relation which exists between the floating surface, or surface presented downward, and the mass of each particle of the load. In other words, it will depend on the specific gravity and comminution of the load. If the specific gravity of the load is but little greater than water, the velocity of the water becomes a very small factor, and the amount which can be transported will be chiefly limited by the containing capacity of the water, but this is a condition not actually found in nature. The difference between the specific gravity of water and load is great, and variable within such small limits that the variability may be neglected ; but the relation between the floating surface and the mass of each particle of load may be determined by another condition than that of specific gravity, 186 STRUCTURAL GEOLOGY. i. e., size; for the ratio between the floating mass of a body, or the surface presented downward, and the mass of the body, increases with the diminu- tion of a body. Then if the body is smaller, the ratio between the floating surface and mass is larger ; and hence comminution promotes flotation. If this comminution is great, approaching complete or molecular comminution, the velocity of the water again becomes a small factor, and the amount of transportation chiefly depends on the containing capacity of the water ; but as comminution is less and the size of the particles larger, some force must intervene to promote flotation, and this is derived from the water power ; and to sustain the same amount of flotation more of this force must be utilized as the size of the particles increase. The amount of this force from which must be drawn the supply in supporting flotation depends, ceteris par- ibus, on the velocity or declivity, but practically the whole force is rarely utilized. The extent to which this force is utilized depends upon many complex conditions by which the motion in the flowing water may be transmitted to the load. To float, the particles of rock must be suspended in the water, and as they fall from suspension during the process of transportation, they must be resuspended, so that the water power must be used in lifting, and this is done by the creation of secondary currents in regurgitation, eddying, boil- ing, &c, or movements in the water transverse or oblique to the direction of the flow, all of which impede the flow. If the flow is perfect no lifting can be done ; so these secondary currents are produced by locally diverting the flow from its normal course, and this diversion to secure lifting must be di- rectly or indirectly upward ; the greater and oftener this diversion the more lifting will be done. In other words, we may say that water power is ap- plied to the lifting of the particles and thus promotes flotation by hetero- geneity of flow, and this heterogeneity of flow is induced by the heterogeneity of channel in both horizontal and vertical direction, but chiefly in the lat- ter. And in obedience to well known laws of friction this heterogeneity of flow is greatly increased by intensifying the flow, or in other words, increas- ing the velocity of the water ; and velocity is due to declivity. And that heterogeneity of channel, which by producing heterogeneity of flow utilizes the water power in lifting the load, is also due to declivity ; and hence it DEGRADATION. 187 remains, first, that the water power, ceteris paribus, is a function of declivity ; and, second, the utilization of the water power, cceteris paribus, is a function of declivity ; so that with a given amount of water and sufficient supply of load, the rate of transportation through the agency of flotation depends on declivity ; and the amount of transportation through driving also depends on declivity. Therefore the rate of transportation of all mechanically com- minuted matter is determined by declivity. I have spoken of the containing capacity of water for load of the same or less specific gravity than water, but the amount of such load is so minute in comparison with the whole amount that we may neglect it. Again, I have spoken of the containing capacity of water for particles of load of greater specific gravity than water ; the amount of matter transported in this way is great, but usually the supply is so limited that the containing capacity is rarely reached ; but it seems probable from observations made on transportation of bad-land detritus that there are times when this con- taining capacity is actually reached, when the amount transported is limited by this condition, that is, containing capacity. Then what is this contain- ing capacity 1 In matter of this character without water the rock power cannot overcome interstitial friction, and hence the matter is not transported. In order that it may be transported by rock power it is necessary, first, that the interstitial spaces shall be filled with water; and, second, that an amount of water be added sufficient to reduce interstitial friction so that it may be overcome by rock power. And it is possible that this can be determined mathematically for particles of any given form, size and weight; but in nature these forms are multifarious, and the determination of the containing capacity is a proper subject of experiment. I know of no such experiments having been made ; but, from observations in nature, I am led to the con- clusion that the containing capacity of water for particles of this nature is at least three times its own weight. Again I must remark that the last mentioned condition of transportation is of very infrequent occurrence; and it remains, then, that in general trans- portation, the rate is determined by declivity. Having now examined the processes of disintegration and transporta- tion separately, we will examine them as combined in the 188 STRUCTURAL GEOLOGY. METHODS OF DEGRADATION. These are, first, erosion or degradation of the general surface; second, corrasion or degradation of the stream channels; and, third, sapping or deg- radation of cliffs. Erosion. — This is distributed over the general surface; the rocks are disintegrated by climatic agencies and transported into streams by the wash of rains, both by driving and flotation, and flotation is largely promoted by the beating of rains. In this method the rate of degradation depends on the rate of transportation. This is a fact of almost universal observation; for wherever there is soil or loose earth, the amount of such matter is the excess of disintegration over transportation. We have already seen in the former analysis of transportation that with a given. quantity of water, transportation will depend on declivity, but in the transportation belonging to this method of degradation the quantity of water is a factor of transportation only to a limited extent, for increased rainfall promotes the growth of vegetation which serves as a protection to the soil. Nor is this protection inconsiderable, for it preserves $he rocks from the beating of the storms, and prevents the waters from gathering rap- idly into rills and brooks, and strains the water of its earthy sediments. I have many times witnessed the action of a storm in an arid region where the disintegrated rocks were unprotected by forests, shrubbery, or turf, and as often have I been impressed with the wonderful power of the infrequent storm to gather up and carry away the land, as compared with the frequent storm in the prairie or forest of a land more richly clad. The same contrast may be observed in a region brought under the dominion of man hj culti- vation where the surface of a plowed field is swept away by a storm, and the furrows are the channels for floods of mud, while the meadow receives the rain with outstretched arms of verdure, which bear it gently to the earth, where it is gathered into quiet rills, which feed a stream made turbid it is true, but pure when compared with the stream of mud flowing from the field from which the plowman was driven by the storm. Erosion, then, or surface degradation is not greatly promoted by increased rainfall, and it may be that its effect is rather to retard the pro- DEGRADATION. 189 cess; but the difference between greater or lesser rainfall is plainly manifest in the topographic features produced — little rainfall giving angular reliefs; much, rounded reliefs. Neglecting such a hypothetic condition as no rainfall, we have in nature to consider only greater or lesser rainfall. With greater rainfall we have a greater power, but a lesser utilization of the power; with lesser rainfall we have lesser power, but greater utilization ; and in these varying conditions, just where maximum degradation is found I am not able to state. Hence, in the process of degradation which I have called erosion, we have simply to consider declivity, with exceptions so minute that they may be neglected. Now, it must be taken into consideration that this is the most import- ant method of degradation, as it acts everywhere on the dry land; but, because its operations are so greatly diffused, being universal in its action on dry land, it is so subtle and minute in its manifestations within any area which may come immediately under the eye that its efficiency is apt to be underrated. Corrasion. — This is the action of waters gathered into streams where their operations are confined to more limited areas, that is, along the chan- nels of such streams. Here the material supplied from the surrounding surfaces by erosion is further transported by the streams, and in the process of transportation becomes the instrument used in disintegrating the stream beds; and the material thus disintegrate'd is added to that furnished bvero- sion, and with it is transported by the streams, and this added material also becomes an instrument of disintegration. The force used in disintegration is rock power and water power; load is the instrument, water the agent. All processes of solution are neglected. The force of rock power and water power is measured by mass into fall, and this may be considered as declivity; the specific gravity of the instrument not being greatly variable may be neglected. There are other conditions of instrument, such as hardness and angularity of particles, which for any given particle might be of value in determining its efficiency; but, in the multifarious particles of diverse hardness and form, a general average will be established for streams, variable within such small limits that these conditions also may be neglected. The only condition of instrument of 190 STRUCTURAL GEOLOGY. sufficient importance to be considered in this connection is size of particles, for the utilization of the particles as instruments is dependent, cceteris paribus, on their size. If the particles be too large they cannot be transported, and thus cannot be used as instruments; and within the limits of size transported, a greater amount of instrument will be used as the size of the particles diminish; that is, with a given stream, the instrument is increased with com- minution of instrument, the instrument being the load, and load being- increased by comminution as has been" seen. We have next to consider the beds to be corraded, and so far as their constitution is a factor in corrasion, it may be brought into the simple expression that heterogeneity promotes corrasion. But a part of the instru- ment of corrasion is derived from the rocks corraded; and as heterogeneity of these rocks promotes disintegration, and to the same extent promotes corra- sion, it further augments the instrument of corrasion in the channel below. But it has been seen that in transportation the utilization of the water power in promoting flotation as a function of heterogeneity of flow is a function of declivity cceteris paribus. Hence, declivity not only increases the force, but it also utilizes the force, and, hence, multiplies itself as a factor of corrasion. A part of the instrument in corrasion is the load of the stream derived from erosion; and we have already seen that the amount of this load depends chiefly upon declivity; hence, the amount of instrument from this source depends on declivity of erosion, and the amount of instrument derived from corrasion depends on declivity; and the power of corrasion, that is, rock power plus water power, depends on declivity. Hence, with a given quan- tity of water and a given character of bed, rate of corrasion depends on declivity. Again, rapid corrasion increases the declivity of erosion, and hence increases erosion; and this increased erosion augments the instru- ment of corrasion, hence, increases corrasion; and declivity by the two methods of degradation enters the general problem of degradation as a factor with a rapidly increasing value. Corrasion is a very important method of degradation, although its results are of much less magnitude than those of erosion. The evidence of this can be seen, and the results often strike the student of physical geography with- great force. The deep channels in which the rivers run are grand topo- DEGRADATION. 191 graphic features. Deep river valleys and mountain gorges are everywhere seen to have been produced by this agency, and the power of the streams in carving their winding paths is readily comprehended. But the magnitude of this agency is more thoroughly brought into visual comprehension in the canons that traverse the Plateau Province, for here erosion has not kept pace with corrasion. All the processes of erosion and sapping serve to obliterate the evidences of corrasion, and the latter appears more plainly as its pro- gress exceeds that of the other methods; but still the evidences of corrasion rarely disappear until the land is buried by the sea; for wherever an area of land is above its base level of degradation, there corrasion will be manifest by deepening its channel; and wherever the dry land has been brought down near to its base level, there corrasion is manifest by widening its channel. There is another method of degradation to be considered, viz : Sapping. — The walls that inclose the channels of corrasion are broken down by gravity, and when in the progress of corrasion the channel of a stream reaches beds which easily disintegrate, having passed through beds which disintegrate but slowly, degradation is increased by an undermining process, and as corrasion still continues through a series of yielding and unyielding beds, the walls of the streams are carried back in a series of steps, the tread of each step being the summit of a harder bed, the rise of each step the escarped edge of the harder bed above, underlaid by the softer. It is manifest that the conditions favorable to the continuation of this cliff degra- dation to any great distance back from the stream are found only where the beds are horizontally, or nearly horizontally stratified. But sapping is not confined to the undermining of walls produced by corrasion, but. is carried on in simple anticlinal upheavals from the axis toward the flanks; in up- heavals of the Uinta type, in like manner, and in the blocks displaced as integers, like those in regions having the Kaibab and other structures, from the elevated to the depressed portions. In these cases the cliffs are produced by the unequal erosion of harder and softer beds wherever upheaval exceeds degradation, and climatic conditions are favorable; and, further, this sap- ping process is carried on in regions of great declivity, where deep channels of corrasion are formed, whatever may be the petrologic conditions, the 192 STRUCTURAL GEOLOGY. alternation of softer and harder beds not being an absolute, but only an accessory condition. In those mountain regions Avhere the rocks are granites, schists, or extravasated masses, every little stream engaged in deepening its channel furnishes conditions favorable to sapping; and so these walls are ever yielding, in small fragments that tumble down from time to time, in large fragments when cliffs or crags topple over, and in great masses by land slides. So wherever cliffs are formed, whether b}7 deep corrasion or unequal erosion, the cliffs themselves are degraded, disintegration beginning with the breaking of the rocks above through atmospheric causes, aided by gravity. Then the rocks are transported by gravity from the higher to lower levels when the disintegration is increased by the fall, and the rocks are left in a condition to be readily transported by the wash of rains or the flow of streams. The extent to which degradation is carried on by this sapping though much less than either of the others, is so great that it must not be neglected in any consideration of this subject. In a mountain region every stream forms cliffs by deep corrasion, and every cliff has a talus in evidence of the efficiency of this method, and we see its effects exhibited in the most remarkable manner in the long lines of cliffs or towering escarpments which stand athwart the Plateau Province. In this method of degradation petrologic conditions may be more or less favorable, but within these conditions the principal factor in determin- ing rate of degradation is declivity. The declivity must be very great for the initiation of the process. With rocks already disintegrated by atmos- pheric agencies, the declivity must be greater than what is usually denomi- nated natural slope ; that is, it must be so great that rock power can over- come friction so as to transport the material to a lower level ; and again, that gravity may be used as a force of disintegration, the declivity must be still further increased, and with this increase of declivitv the rate of dis- integration and transportation by falling is increased at a great ratio until the rocks are undermined, when the conditions again multiply the power. But rapid corrasion, which depends on declivity, increases sapping ; and sapping, which depends on declivity, increases corrasion by adding to the DEGRADATION. li>:> instrument of corrasion, and again declivity is multiplied as a -factor in degradation. To this rule that sapping promotes corrasion by adding to the instru- ment of corrasion, there are three curious exceptions, one of which is of great importance. The first is where the cliff produced by deep corrasion, before it has retreated from the bank of the stream, tumbles down so as to choke the stream. In this case the material falling from the cliffs serves to protect the underlying stream bed, and, so far as it ponds the water up stream, it causes it to precipitate its load, and thus deprives it of the instrument of corrasion. But this fallen matter is rapidly attacked by the stream, is soon taken up as load, and used as an instrument of corrasion. The second exception is where a lateral stream enters a main one, the lateral stream having so great a declivity' as to be able to transport great quantities of coarse material during local flood time, or that flood time which pertains to the secondary stream, but not to the primary. In this case it may sweep along its greatly-inclined bed into the main channel, load derived from sapping, or even from erosion, which cannot be farther transported by the main stream, and this new matter for the time being serves as a protection to the bed of the main stream. In the Colorado River, with very few exceptions, all the falls and rapids which beset its course through the great canons are caused by dams made by side streams having great declivity. A few of the falls are made by dams formed by the sapping of the immediate cliffs of the main river. The third exception is found where streams having great declivity run through beds of incoherent sands. Here load is rapidly added to the stream by gravity, and the stream not being confined by water tight rocks, its waters penetrate the interstitial spaces of the sands and serve to overcome the friction of slope, and thus assist rock power in transporting the sand into the stream. Here the stream cannot have high banks, and the channel is greatly widened and is engaged in transporting load furnished it from the sides, and can make but little progress in corrasion, for every particle car- ried from the bottom of the stream is rapidly replaced by one from the sides. This condition is finely illustrated in many places along the course of the Virgin River, a tributary of the Colorado. In one place where its l:^ r a 194 STRUCTURAL GEOLOGY. course is through indurated and homogeneous rocks, its channel is from 20 to 50 feet in width, and from 1,500 to 3,000 feet in depth; it runs through a narrow but profound gorge. But when it passes a well defined geologi- cal horizon from these coherent into extremely incoherent beds, its channel abruptly widens, and the stream is a broad sheet of water many hundreds of yards in width and but a few inches in depth. Again this condition is well illustrated in the Platte River where it crosses the Plains. Here the beds through which the river runs are incoherent, and although* the river has as great a fall as the Colorado through the plateaus, and although the climatic conditions are essentially the same, yet the former runs in a broad sheet scarcely below the level of the plain, while the latter runs in a narrow groove at profound depths below the general surface. Thus it is that the streams, though they may have great fall, and though the stream beds may be of material that can be rapidly transported, yet they do not succeed in excavating deep channels, for every particle taken from the bottom is re- placed. Nevertheless general degradation is carried on by such streams at a rapid rate, but not at a maximum rate, for the water permeating the sands on either side is steadily and rapidly evaporated, and is thus lost as an agent of degradation. There are many streams in the arid region of America, running alternately through harder and softer beds, which are continuously degrading the coherent rocks and intermittently degrading the incoherent rocks ; that is, the streams are ever living where the beds are coherent, but when they reach the sands the waters sink and re-appear where the beds below are harder. Through these harder beds the streams cation, and through the softer beds low plains stretch either way from the course of the stream ; and it is only during flood time that the channels are cut across these plains from canon to canon. But dropping these exceptions, all of them interesting cases, let us return to the main argument. We have seen that ever are the effects of declivity in degradation multiplied directly and indirectly. Wherever the rate of degradation by any one method 'is increased it is due chiefly to increased declivity, and wherever the rate of one method of degradation is increased, the rate of all other methods is increased. We may not be able to give mathematic expression to rate of degrada- DEGRADATION. 195 tion in terms of declivity, but Hopkins and Babbage have shown that the power to transport load of a given size of particles increases with the sixth power of the velocity of water, and it is probable that the rate of degrada- tion increases with the velocity of water in very nearly the same ratio, but modified slightly by a multiplicity of climatic and petrologic conditions. It will be seen that in the above discussion I have neglected one term of climate, that is temperature. My field of study has been limited to the frigid and temperate climates, and for the effect of a torrid climate I have no facts to guide me to valid conclusions, but within my field of study the temperature term, though modifying the methods and topographic results of degradation, does not invalidate the result I have reached as to the over- shadowing importance of declivity. Increased cold diminishes the protec- tion derived from vegetation and permits greater rainfall to produce greater degradation. But in a given latitude increased cold is due to increased ele- vation. (This increased elevation is also increased declivity.) But this is again modified by the fact that moisture descends as snow, and to that extent the beating power of rains is lost. Where these snows accumulate as ice, forming glaciers, another modification of degradation is introduced, dimin- ishing the effects of the water in degradation and changing the topographic features; that is, any given amount of precipitation of water will produce more degradation acting as rains and rivers than as snows and glaciers. By the former condition atmospheric disintegration is more rapid, and corrasion is confined to narrower channels, and thus sapping is promoted. Transporta- tion in ice and water are governed by the same conditions of flotation, and the greater heterogeneity of river channel promotes greater flotation, so that degradation in each of its elements of disintegration and transportation is faster by rains and rivers than by snows and glaciers. Hence, as cold increases, degradation is promoted by the decrease of protection derived from vegetation until that degree of cold is reached where the moisture is precipitated as snow, when low temperature serves to decrease degradation. Having considered all the modifying conditions of climate and petrol- ogy, it yet remains that degradation increases with declivity through the combined forces of water power and rock power in a rapidly-multiplying rate from that low degree of declivity which permits the transportation of 196 STRUCTURAL GEOLOGY. finely-comminuted load to that high degree of declivity which permits the load to be moved by its own gravity, when the effect of declivity is again multiplied at a still higher rate until verlicality is reached and undermining begins and another multiplication of the effect of declivity ensues. There are conditions of degradation in the extremes of declivity worthy of mention. In high degrees of declivity transportation in a horizontal direction is limited, the cliffs soon tumble down, and degradation by this process ceases. In a very low degree of declivity approaching horizontally the power of transporting material is also very small. The degradation of the last few inches of a broad area of land above the level of the sea would require a longer time than all the thousands of feet which might have been above it, so far as this degradation depends on mechanical processes — that is, driving or flotation; but here the disintegration by solution and the transportation of the material by the agency of fluidity come in to assist the slow processes of mechanical degradation, and finally perform the chief part of the task. We may now conclude that the higher the mountain, the more rapid its degradation ; that high mountains cannot live much longer than low mount- ains, and that mountains cannot remain long as mountains; they are ephem- eral topographic forms. Geologically all existing mountains are recent; the ancient mountains are gone. But existing mountains may be old or young as compared with other existing mountains. We may speak of the age of mountains, referring to the age of the rocks of which they are com- posed, but this will have no reference to the age of the mountain form. We may speak of the age of a mountain with respect to the inception of the up- heaval which exposed the rocks to that degradation which has produced the mountain form; and this epoch will not be very long ago, geologically, for the rate of upheaval must be greater than the rate of degradation, else mountain forms will not be produced. We may speak of the age of mount- ains, referring to the completion of the upheaval by which the mountain forms were produced through degradation ; the time which has elapsed since the epoch to which we then refer must be short indeed; but if, in speaking of the age of mountains, we refer to the time when those topographic forms were produced, they are all newly born. DEGRADATION. VM Having1 found that degradation is accelerated by increased declivity at a high rate, let us apply this law to the degradation of the Uinta uplift and see what topographic features would have been produced if the uplift had been abrupt or greatly faster than degradation. As the area was uplifted in large part as an integer, its steep flanks would then have been regions of great declivity, while its axial region would have comparatively gentle slopes, and as the first streams heading alon«' the axis ran toward the flanks, these streams would not only have had channels suddenly increasing in declivity at the flanks, but the amount of water carried by the streams would have, steadily increased from axis to flanks, and hence corrasion on the flanks would have proceeded at a rate determined by these multiplied causes. As the main channels were thus corraded all the lateral channels would in like manner have been rapidly corraded ; this would have induced rapid sapping and rapid erosion, and the degradation along the flanks would have far exceeded degradation along the axis, and this would have resulted in the production of an ever narrowing axial ridge. An examination of the map reveals the fact that these are not the topographic characteristics of the Uinta Mountains. The axial region is higher in the western portion of that part of the range under consideration, but the difference in elevation between the flanks and axis is inconsiderable when compared with the whole amount of degradation; while in the eastern portion of the part of the range under consideration the axial region is much lower than the flanking region on either side. Here the excess of degradation in the axial region is accounted for by remembering that the degradation of consequent drainage has been assisted by the degradation resulting from extra limital or through drainage. But in the former case, i. e., the western portion of the region under consideration, the drainage is all consequent on the upheaval, and to account for the plateau like character of the region, we have to suppose either that the elevation being constant has been but little faster than degradation, or else that elevation has been intermittent, Let us further consider these two hypotheses, one of which must be true. If elevation was constant but slow, the axial region was first attacked by degradation, and as it was slowly uplifted, degradation kept this axial 198 STKUCTUKAL GEOLOGY. region down so that an axial ridge was not produced. If elevation was intermittent it might have been fast for a time, and then ceased until the region was planed down to a general level now represented only by the summits of the highest peaks, and then a neAv upheaval carried it to its present elevation. But the rate of this last uplift must have been slow or the axial ridge would have been more pronounced, and hence we may infer that the elevation was either slow by continuous motion, or what would be its equivalent, slow through intermission of movement, with the last epoch of elevation slow. Further light will be thrown on this subject when we consider sedimentation. It is manifest that if elevation was slow so that degradation progressed nearly as fast as displacement, then degradation was slow. Again consider the amount of degradation. From this portion of the Uinta range a block three and one-half miles in thickness has been carried away, all since "the close of Mesozoic Age ; and for this degradation the declivity was small so that its progress was slow, and we have some conception of the amount of time which has elapsed since the beginning of the Uinta upheaval. SCHOLIUM. Let us now turn aside for a moment from the main argument to consider a statement which I have elsewhere made concerning the Basin Ranges. These are monoclinal ridges of displacement, of narrow base and steep declivities where conditions for rapid degradation obtain, but the amount of degrada- tion of any Basin Range is exceedingly small as compared with the Uinta Range, and we are forced to conclude that the epoch of its upheaval is much later than that of the inception of the Uinta uplift, but may be of about the same date as the last throw of the Uinta displacement. SEDIMENTATION. Soon after the inception of this upheaval, sedimentation began on either flank and continued during the progress of the uplift until on the north side more than 6,000 feet of sandstones and shales had been deposited, and where the Brown's Park beds overlap Bridger beds about 8,000 feet. On the south side also there was a great accumulation, the extent and cliarac- SEDIMENTATION. 199 teristics of which are not yet fully known. Geologists will understand that the thicknesses given refer only to the beds which remain to be studied. There may have been much greater sedimentation ; beds may have been formed during periods of sedimentation which were carried away during periods of dry land conditions, and especially during the last great period of degradation not yet ended, and of which sediments there are no residuary fragments attesting to their former existence. On both sides of the range, but especially to the north, we know that the progress of sedimentation was interrupted by periods of dry land con- ditions. These dry land conditions prevailed over a large area during the epoch separating the Lower Green River from the Briclger period, but a part of this interval of time at least was occupied in sedimentation over a portion of the great lacustrine area. Again, a period of dry land con- ditions prevailed between the deposition of the Bridger and the Brown's Park Groups. The latter was deposited over areas in the region of uplift beyond the reaches of the antecedent lakes represented by the four lower Cenozoic groups. How far the Brown's Park Lake extended over the region which had previously been occupied by the waters in which the earlier Tertiary sediments were deposited we do not know. Wherever the overlap of the Brown's Park beds on the Lower Cenozoic groups has been studied the former terminate in escarpments, and no evidence of shore line has been seen. The Bishop Mountain Conglomerate which has been found to lie uncon- formably on all the other geological formations of this region, except the Brown's Park, and possibly on this latter also, is neither a marine nor lacustrine deposit, but is believed to be a subaerial gravel. It is possible many geologists would ascribe it to the action of ice, but in any case it need not be considered in our account of sedimentation. Such were the general changes from emergence to submergence through- out the region of downthrow, but there was a narrow belt of country between the general region of uplift and the general region of downthrow which was subject to more frequent changes than the greater ones described above. We find, first, that there are many overlaps, i. e., that later beds extend beyond the limits of earlier beds. To accomplish this result it is manifest that the waters of the lakes must have risen or the land subsided. Again, 200 STRUCTURAL GEOLOGY. we find that certain beds thin ont shoreward. It is manifest in this case that the waters of the lakes must have fallen or the land Lave risen. Again, we find upper lake beds unconformable on lower lake beds. Here it is manifest that a dry land period separated their deposition, and that displace- ment occurred. These outthinnings, overlapping, and unconformities appear from time to time from the base to the summit of all the fresh water beds older than the Brown's Park. There are some other interesting facts relating to the belt under con- sideration, viz, the appearance of many conglomerates which are rapidly changed into sandstones in a direction farther from shore. These conglom- erates are found to be made up of the more or less water- worn fragments of limestones, sandstones, and quartzites similar to those outcroppings in the mountain region or area of uplift, and often contain the same fossils, leading us to conclude that they are derived from that region. It should be remarked here that the appearance of these conglomerates, together with the overlappings, outthinnings, and unconformities before mentioned, furnish the evidence on which we decide that this was the old shore-line, and that the lake beds were never continuous over the great Uinta area. On the other hand, the fact that no such phenomena have been observed in the outcroppings of the Mesozoic and Paleozoic beds leads us to conclude that they were at one time continuous over the Uinta area, and this is strengthened by the fact that in all these lower groups any bed found on the one flank re-appears on the other with all its lithologic character- istics; and it is thus that we fix the epoch of the inception of the Uinta upheaval after the close of the deposition of the Upper Hogback Sandstone of the Point of Rocks Group, and before the deposition of the lowest bed of the Bitter Creek formation. Returning again to the consideration of sedimentation in the region of downthrow in its relation to displacement and degradation in the region of uplift, we have first to consider the amount of sedimentation or building up of the sediments on the flanks of the uplifts to the extent of many thousand of feet ; next, the general unconformities which separate some of the forma- tions ; and, lastly, the minor unconformities, overlappings, and outthinnings observed in the zone of ancient shore-lines. From all these facts it appears UINTA MOUNTAINS— RECAPITULATION. 201 that displacement, degradation, and sedimentation were in a general way simultaneous and continuous up to the close of the Bridger period, but interrupted by many minor cessations in the progress of displacement and some cessations in the progress of deposition, and that between' the Bridger and Brown's Park periods there was a long- time when no sediments were accumulated. The Uinta uplift in the region of Brown's Park was at one time several thousand feet greater than we have represented it to be, but after the deposi- tion of the Brown's Park beds it fell down that much ; the evidence of this will more fully appear when we have discussed the Yampa plateau, Diamond Peak, the Dry Mountains, and Brown's Park. RECAPITULATION. We will now recapitulate some of the important conclusions reached in the study of the geology of the Uinta Mountains. First, the upheaval began at the close of the Mesozoic Age, and continued with slight intermis- sions until after the Bridger period, and the total amount of upheaval in the axial region was more than 30,000 feet. The region was upheaved partly as an integer and partly as a body of minute parts. Second, pari passu with upheaval degradation progressed, and in some places along the axial portions of the region this degradation amounts to more than 25,000 feet, and the mean degradation is three and one-half miles, and from the entire area there has been a total degradation of 7,095 cubic miles. While we have no means of determining any absolute rate of degradation, we are led to con- clude that a maximum rate was not established ; that, as upheaval was slow, degradation was slow. Third, pari passu with displacement and degrada- tion in the region of uplift, there was sedimentation in the region of down- throw. This sedimentation was sometimes intermittent over large areas, frequently intermittent along the shore-line zones. These sediments were derived in part at least from the region of uplift, but probably mingled with materials brought from districts not embraced in the region under discussion. On the north side of the mountains the amount of sedimentation was more than 6,000 feet, and where the Brown's Park beds overlap Bridger beds the amount of sedimentation was about 8,000 feet. 202 STKUOTUliAL GEOLOGY. THE YAMPA PLATEAU. DISPLACEMENT. The structural sections of Plate I embrace not only the Uinta Mountain region, but also extend over the region which I have designated as the Yampa Plateau. The facts relating to the present position of the formations are there fully set forth. On Plate V we have separated the stereogram of the Yampa region from the general stereogram, Plate III. Referring to Plate V, attention is called to the Island Park sag d, d, to the Echo Park sag e, to the Split Mountain cusp c, to the monoclinal flexure of Cliff Creek m, m, m, to the Fox Creek flexure f, and to the Yampa fault g, g, which branches midway in its course. A comparison of this stereogram with the geological map will be instructive. The Yrampa Plateau is on the south side of the Uinta Mountains, and all the lines of displacement in the stereogram, except the Yrampa fault, show the upheaval to be northward corresponding to the general upheaval of the Uinta Mountains, but the exception mentioned exhibits a northward throw. This great displacement is a flexure at its eastern end ; but it finally changes into a dragged fault, where the thrown beds are flexed upward at the end, and then into a clean fault ; midway in its course it branches ; the northern branch is a fault as far as it has been traced ; the southern branch changes from a fault to a monoclinal flexure, and finally these branches of the great displacement fade out, but in a manner not clearly understood, as the region is marked by an accumulation of late subaerial gravels, by soil and by vegetation, and on the stereogram this uncertain area has been rep- resented by broken lines. By referring to the map it will be seen that the main fault with its branches is represented in the topography of the country by bold cliffs. These lines of cliffs are broken by many deep gorges of corrasion descending from the plateau to the lowlands where the stratigraphy is plainly revealed, and the lower beds of Triassic sandstone are seen on the same geographic level as the upper beds of Uinta Sandstone, so that the total displacement is about 5,000 feet. These cliffs are due immediately to THE YAMPA PLATEAU. 203 displacement ; where this displacement is by faulting the cliffs are escarp- ments, but where it is by flexure the flexed beds remain, and the slope of the cliffs conforms in a general way with the dip of the strata. Hence these lines of cliffs have not receded from the locus of displacement, although they are so precipitous as so furnish conditions favorable to rapid degradation hy direct sapping, corrasion, and general erosion. From these facts we inevi- tably conclude that the displacement is of late date. But the Triassic beds on the upheaved side are gone, and in many places a great thickness of Carboniferous beds also, while on the thrown side a notable thickness of Trias yet remains. The non-recession of the cliffs proves that the displace- ment was not ended long ago, if indeed the movement has yet ceased, while the occurrence of the beds on the thrown, side, which have been degraded from the upheaved side, lead us to refer the inception of the upheaval to an epoch of much earlier date, and to infer that the displacement was slow, yet not so slow that degradation was able to keep apace. When we come hereafter to discuss the relation of this displacement to other facts of displacement, degradation, and sedimentation, it will appear that this displacement was not upheaval in relation to the general region under discussion in this chapter, but was in fact downthrow, whatever it might have been in relation to the level of the sea or in that other relation, which yet may be a very different thing, i. e., to the center of the earth. SCHOLIUM. Early in this volume I distinctly denned my use of the terms "upheaval" "subsidence," "uplift," and "downthrow," and restricted the meaning of these words in such a manner that they should relate only to adjacent and compared beds of rock, but I recognize three categories of relations that may be expressed by these terms, viz, the relation of parts of a geological horizon to each other, the relation of parts of a geological horizon to the level of the sea, and the relation of parts of a geological horizon to the center of the earth. For these several categories it would be a great advantage to geological science, by leading to greater simplicity and precision of de- scription and to clearer conceptions, if different verbal representatives could be used for the different ideas. 204 STRUCTURAL GEOLOGY. DEGRADATION. The amount of degradation in the region of the Yampa Plateau though less than in the Uinta region as defined above, is still great. The maximum degradation is found at the few points where deep canons cut the cliffs of the Yampa fault, and Uinta Sandstone is found in the floor. In these places there has been more than 15,000 feet carried away since the close of Mesozoic time ; the mean degradation over the entire area has been 8,000 feet, or a little more than one and a half miles, and the total more than 1,200 cubic miles. SEDIMENTATION. A part of the rock material taken from this region was doubtless deposited in the Tertiary lake region to the south, another portion probably into the Brown's Park Lake, and still another and very considerable portion has been carried away by the Colorado River to the distant sea. JUNCTION MOUNTAIN. This district was studied in the earlier years of the exploration of the region, and since that time it has not been carefully reviewed. In my notes I make mention of a fault running in a north and south direction to the east of the axis of upheaval, with a throw to the westward, but the magnitude and general characteristics of the fault are not given. The sections given in Chapter I of this volume, figures 1 and 2, represent the idea of its structure obtained at the time it was studied, but subsequent years of observation in other regions lead me to place no great value on the observations made and conclusions reached at that time. DIAMOND PEAK. To the north of O-wi-yu-kuts Plateau is Diamond Peak. The principal mass of the mountain is on the north side of the great Uinta fault, but the foot of the mountain stretches across from the thrown to the upheaved side of the fault, For a long time this mountain was an enigma. From its position it DIAMOND PEAK. 205 ought to be a monoclinal ridge, but it is. not Again, its base rises chiefly from the thrown side of the fault, but its summit rises many hundreds of feet higher than the plateau on the upheaved side of the fault, and it seems to stand as a contradiction to all known laws of the progress of degrada- tion. On a first visit to the mountain no clew to- this enigma was obtained ; on a second visit a better understanding of its lithologic constitution was obtained; and on a third and final visit, which was somewhat protracted, it is believed that the problem was solved. All that portion of the base of the peak north of the fault is composed of beds of the Bitter Creek period lying horizontally. On the horizontal beds sandstones and limestones are piled in confusion. In the sandstones no fossils were found, but they resemble lithologically the sandstones of Carboniferous Age. The limestones contain Carboniferous fossils. We have in fact a huge pile of Carboniferous rocks resting on a base of horizon- tal Tertiary sandstones. Now to explain how rocks of an older horizon were piled on a later, we have a fact which was discovered after the second visit, but before the third, viz, that there had been two movements along the line of this fault in opposite directions. By the first movement the Uinta or upheaved side was carried about 3,000 feet higher in relation to the beds on the north side than now appears. Subsequently by a reverse movement it fell back the 3,000 feet. After the former displacement and before the latter, we may reasonably suppose that here a great cliff faced northward, for the total displacement by faulting was about 23,000 feet, and the only hypothesis necessary to the explanation of such a line of cliffs is that displacement was in its later development faster than degradation. Such cliffs would rapidly tumble down, and beds of Carboniferous Age might thus be placed on beds of Tertiary Age. But further, immediately to the west and immediately to the east along this zone of displacement, the line of faulting in its meanders back and forth through the zone of flexure, which has heretofore been described, passes some distance from the upheaved side of the zone toward the thrown side, and hence the beds on the upheaved side dip at a great angle to the northward, and are in a position to more readily tumble down, and doubtless this condition obtained where the 200 STRUCTURAL GEOLOGY. O-wi-yu-kuts cliff overhung the Tertiary sandstones that form the base of Diamond Peak. This double movement along- the plane of the Uinta fault is seen farther west beyond Red Creek, where it was first discovered, and where the sandstones of the Point of Rocks period are found to have been dragged down by the later and southward throw. Similar evidences are seen farther eastward, between Diamond Peak and Red Creek, and the topographic features of the region in like manner give evidence of the later movement, for some of the peaks composed of Bitter Creek sand- stones are higher than the mountains and plateaus of quartzite and Uinta Sandstone. To the east of Diamond Peak this second displacement did not follow the old plane of faulting, but trended irregularly northward and bent downward the edges of the beds which originally abutted against the southern wall of the fault, which was composed of Uinta Sandstone and underlying rocks. Subsequent degradation has carried away the upper part of these beds that were turned down, and we now see fragments standing on edge and the younger beds are on the south side, the older beds on the north side, a fact which I have stated in a former chapter, and which is thus explained. But we have still further evidence of this later throw on the south side. The beds of the Brown's Park Lake were deposited against the foot of Diamond Peak, and this later displacement was subsequent to the deposition of these beds, and the plane of faulting cuts them in twain. Those fragments on the north side of the fault lie high upon the side of Diamond Peak, while the beds on the south side of the fault are low down in the valley at the foot of the peak. The latter are nearly horizontal ; the former have a general dip southward, but are broken and greatly contorted. This mountain, of origin so strange, was curiously enough the scene of the great diamond bubble, so skillfully burst by my brother geologist, Clarence King. THE DRY MOUNTAINS. This low range of mountains extends in a southeasterly direction from Vermilion Creek to the Snake River, and, topographically, appears to be a THE DRY MOUNTAINS. 207 continuation of the great monoclinal ridge of Carboniferous sandstone north- east of Po Canon, but, in fact, these mountains are made up of beds of Ter- tiary Age, though there are outcrops of Mesozoic beds in the depths of the deeper gulches. * This range marks the continuation of the displacement that I have called the great Uinta fault, and the evidences of the reverse movement are complete. The first movement, which was upheaval on the Uinta side and throw on the northeast side, seems to have been by monoclinal flexure, while the last movement, which was throw on the Uinta side and upheaval on the northeast side, was in part by flexure and in part by fracture. But in the period of time separating the two movements the Brown's Park beds were deposited across the zone of original flexure which had been greatly degraded ; still farther to the northwest there is another line of displacement approximately parallel to the first, with its throw also on the southwest side, corresponding in this respect with the throw of the last displacement in the Dry Mountain district. This northeast displacement fades out in a northwest direction, and entirely disappears at the divide between the water-shed of the Vermilion and the water-shed of the Snake River. When it is first seen near this divide it is a gentle monoclinal flexure, and steadily increases in abruptness along its line in a northeasterly direction until the bluffs of the Snake River are reached, where it is seen as a dragged fault, There seems to be no doubt that these displacements having throws to the southwest were synchronous, while the evidence that the monoclinal flexure with throw to the northeast was of earlier date is complete, for between the two periods the Brown's Park beds were deposited — that is, the Brown's Park beds are seen to have been involved in the displacement having a southwest throw, but took no part in the displacement with a northeast throw, as tins last dis- placement was made and the beds involved in it were truncated prior to the deposition of the Brown's Park beds, and these beds were placed over their upturned edges. In the Dry Mountains some interesting facts have been observed. Along or near to the line of double or reverse displacements we sometimes find an escarpment facing the southwest, composed of beds of the Bridger period, or of still lower Cenozoic rocks, and dipping back toward the north- 208 STRUCTURAL GEOLOGY. east, but as often we find escarpments facing the northeast composed of beds of the Brown's Park period, horizontal or gently dipping to the south- west, i. c, the escarpments of this range are sometimes reversed, because of the reverse movement along the planes of fracture or the zone of flexure. BROWN'S PARK. In this discussion I shall not only include Brown's Park proper, but a district of country stretching to the southwest, between the Dry Mountains and Escalante Peaks to the Snake River. Here we have a geological basin with a floor of Uinta Sandstone and Carboniferous and Mesozoic rocks. Its longest diameter is in the same direction as the axis of the Uinta uplift, and while the basin extends somewhat southward across the axis, yet the larger part of the basin is on the north side of the axis. But the old lake basin extended eastward and northward far beyond the area included in the Uinta uplift and beyond the present channel of the Snake River, and here the floor is unknown; but this latter region is not within the limits of present discussion. Within the region under discussion on the floor of the old lake basin beds of the Brown's Park period were deposited; these beds lie chiefly in a horizontal position, but on the north side of Brown's Park the beds are abruptly turned up against the Uinta Sandstone of the O-wi-yu-kuts Plateau, with a dip of about twenty-five degrees. Farther to the east, near the divide between the waters of the Green and the Snake, south of the monoclinal flexure and fault of the Dry Mountains, a deep synclinal flexure is observed; parallel with it and still farther south another of less magnitude, and still beyond a third but slightly developed. Let us noAV consider the effect which the reverse throw along the great Uinta fault and the throw along the Yampa fault has had on this valley. In the. former the downthrow at Red Creek is perhaps less than 1,000 feet; at Diamond Peak, about 3,000 feet; and the total throw of the two displace- ments in the Dry Mountains and vicinity is probably more than 4,000 feet. The throw of the Yampa fault, from its inception on the west, soon attains a magnitude of 5,000 feet, and where it is lost by transverse structure, near Junction Mountain, it is about 3,000 feet. Thus it is seen that the great block between these two faults has fallen down from 1,000 to 5,000 feet in BROWN'S PARK— ASPEN MOUNTAIN DISTRICT. 209 its different portions. Prior to this downthrow there was a great elevated valley drained into the Green River. When the downthrow commenced it is probable that the Brown's Park beds were not yet deposited, but after it had continued for some time the region was so depressed that the waters of the stream were ponded and a lake formed. In this lake, then, the Brown's Park beds were accumulated. We know that the Brown's Park beds were involved in a part at leasi of this downthrow, and hence were deposited before the downthrow was accomplished, because the beds themselves were involved in the displace- ment; they are severed by faults and bent by fractures where they are seen to overlap or extend beyond the area of downthrow. Hence it is seen that Brown's Park is not a valley of displacement or of subsidence, but was originally formed as a valley of degradation — an elevated valley in a mountain region. It subsided or fell down as a part of a greater block. But the whole of it did not thus subside, for the Dry Mount- ains stand across the site of this ancient depression. ASPEN MOUNTAIN DISTRICT. In this district we have a great upheaval with its axis in a north and south direction, at right angles to the Uinta upheaval. On either side of the upheaval there are zones of maximum flexure. The beds brought to view in the degradation of this upheaval are all the Cretaceous formations above the Henry's Fork Group and all the Cenozoic groups below the Brown's Park; hence the inception of this upheaval dates from some epoch in Post-Bridger time. The whole of the uplift is not within the area embraced in the map. The section, together with the geological map, presents all the important characteristics of this uplift, but there are some minor features of interest. In the northwest, northeast, and southeast angles or corners of the uplift there are many minor faults normal to the strike of the beds. Quien Hornet Mountain stands on the southwest corner. No faults have been discovered here. There is a gentle synclinal between the end of the Aspen Mountain uplift and the side of the Uinta uplift. At the south end of the uplift the axis passes through the eastern end of Aspen Mountain. Farther north- 14 p a 210 STRUCTURAL GEOLOGY. ward the axial region, topographically, is a valley, for Bitter Creek divides the uplift, a stream having an extra limital source — a stream whose course was determined antecedent to the uplift. In the heart of the uplift Cretaceous beds of extreme friability are found, and the secondary drainage or lateral wet-weather tributaries to Bitter Creek have excavated these valleys to the very heart of the uplift. • Here 10,000 feet of beds have been carried aw*ay by the waters since the inception of the uplift. INDEX Pago. Amplcxus zaplirentiformis 107 Ancliura prolabiata - 121 rnida , - 120 Anticlinal Structure 10,17,24 Appalachian Mountains 24 Structure 9,24 Area Coalvillensis 115 Archa:ocidaris cratis 10(J Avicula Parkensis 115 Aspen Mountain 160 district 153 , Structure of 209 Bannister, Dr. H. M 48 Basin Province 6, 7, 29 , Orographic structure of , 23 , Summary of history of 32 Eanges 6, 24 , Sedimentary rocks of „ 8 Eange Structure , 16,17,19,24,29 Bellerophon carbonarius Cox, var. subpapillosus 92 Bishop Mountain Conglomerate, Distribution of 169 relations 62,165,170,199 type localities 44 Bitter Creek Group, Distribution of 162 , relations 64, 162 , type localities 45 Black Butte 160 Quartzite 160 Blake, Prof. W. P., on the Plateau Province 3 Bridger Group, Distribution of 167 , Fossils of 105 , relations ^3, 167, 199 , type localities 45 Brown's Park Group, Distribution of 168 , relations 63,199,208 , Structure of 208 Group, type localities 44 Bruce Mountain ' 163 Butte, Black 160 , Pilot 18,25 Buttes 15 Cameo mountains 15 Cameo Mountains 15 Structure 15 211 212 INDEX. Page. Camptonectes platessiformis 93 Canon of Desolation, Later views ou fossils from IX Carboniferous Period, fossils of * 88 Catalogue of fossils 88 Cliffs of Displacement 14 ' Erosion 15 Colorado River 193 Conformity of the Cretaceous 156 Copo, Prof. E. D., on separation of Tertiary and Cretaceous 72 Washiki Group C5,G6 Corbicula Powelli 127 Corbula subuudifera 129 Corrasion 189 Correlation of Cretaceous and Tertiary Groups 71 Cretaceous Period, fossils of 94, 101 Cyrena (Veloritiua) erccta 117 Declivity as a condition of degradation 184,186,187,189,192,195,197 Descriptions of new species of fossils 107 Degradation , 182 , Methods of 188 of the Uinta Mountains 181 Drsolation, Canon of, Later views ou fossils from IX Diamond Peak 104 Structure of 204 Disintegration 182 Dynamics of 183 Displacement, Cliffs of 14 diagrams 174 .Diverse 16,17,25,29,31 , Slopes of i 14 , Types of #17 of the Uinta Mountains 176 , Zones of diverse 16,17 Diverse displacement 16, 17, 25, 29, 31 Drainage, Antecedent and superimposed 12 , Reversed 35 of the three geological provinces 7 Drift 171 Dry Mountaius, Structure of ; i 206 Dnttou, Capt. C. E., on Black Butte Quartzite 160 Dutton, Capt. C. E., on reversed drainage 35 Ellsworth, Mount 20 Epochs soparatiug groups 61 Erisocrinus typus 89 Erosion 188 as a measure of geological time 33 , Conditions affecting rapidity of 34 Eruptive mountaius 36 , Types of 18,22 Eupachycrinus platy basis 108 Flaming Gorge district 146 Group, Distribution of 151 , Fossils of ,. 92 , relations 68 , Section of 152 INDEX. 213 1**1110. Flaming Gorge Group, typo localities 51 Flexure, Maximum _ jo Flotation _ fc 1^ Fossils, Catalogue of yy .Cretaceous, from beyond the limits of the Plateau Province 101 , Descriptions of new species of 107 of the Bitter Creek Group 102 Bridger Group 1 05 Brown's Park Group 10G Carboniferous Period .-- Cretaceous Period 94 Flaming Gorge Group 0 216 INDEX. Page. Kuiii-fall and orosion 188 lied Creek Group, Distribution of 137 , relations 70 , typo localities 02 Wall Group, Distribution of 47 , Sectious of 57 , typo localities 55 Rby topborus Meekii 118 Richard's Peak 163 Ridges, Monoclinal 11, 13, 14, 10 , Projecting 13, 15 River, Colorado . 1U3 , Platte 194 , Virgin 193 , Yampa 11 Rocky Mountains defined 5 Rogers, Messrs . . . 9, 24 Routes of travel - VI Salt Wells Group, Distribution of ... 154 , Fossils of - 1)7 , relations 00 , Sections of 157, 159 , type localities . . 49 San Francisco Mountain 20 Sapping 191 Sectious, Structure 173 Sedimentary groups, Distribution of, in the three geological provinces 8 of the Plateau Province i 37 , Table of 40 Sedimentation . 198 Sbinarump Group, Distribution of 150 , relations 08 , Sections of 53, 112 , type localities 54 Shore-line of Mesozoic and Tertiary seas 30 Stereogram 175 Steward, Mr. John F 57, 142 Structural geology of the Uinta Mountains 170 Structure, Anticlinal 10, 17, 24 , Appalachian 9, 24 , Basin Range 10,17,24,29,198 , Cameo 15 , Henry Mountain 20 , Kaibab 14,17,28,29,30 , Orographic, of the Basin Province 23 Park Province 20 Plateau Province 25 , Summary of orographic 29 sections 173 Structures, Orographic 9, 21 Structure, Table Mountain 18 , Tushar 19,25,20 , Uiukaret 18 , Uinta. 11,17,20,28,30 , Volcanic 19 INDEX. 217 Page. Subproviuce, Sevier and Rio Virgen 31 Wasatch 31 Succinea papillispira .' 129 Snlphur Creek Group, Distribution of 154 , Fossils of 95 , relations GG , Sections of 157, 160 , type localities 50 Table Mountain Structure 18 Tertiary Period, Fossils of 102,100 Tonto Group, relations 70 , Section of 57 , type loc£ilities 5G Transportation, Dynamics of 184 Tulotoma Thompsoni 134 Turnus spberoides 117 Tusbar Structure 19,25,26 Unkaret Mountains '. „ 26 Structure 18 Uinta Group, Distribution of 141 , overlap on Red Creek qnartzite 139 , relations 70, 138, 144 , Section of .- 143 , type localities 61 Mountains 11,125,136,173 , Degradation of. 197 , Geology of 136 , Recapitulation of history of 201 , Unconformities of 129 Structure 11,17,26,28,30 Unconformity at summit of Uinta Group 144 Red Creek 139 Unio brachyopisthus 12G goniouotus 116 petrinus 125 propheticns 125 Shoshouensis 126 Stewardi 110 Upper Aubrey Group, Distribution of 149 , Fossils of 91 , Sections of 57 , type localities 54 Upper Green River Group, Distribution of %. 167 , Fossils of ,Jr.. 104 , relations 63, 167 , type localities 45 Vermilion Cliff Group, Distribution of ;./ 151 , relations G8 , Section of 53,152 j typo locality 54 Virgin River 193 Viviparus Pauguitchensis 123 plicapressus 133 Volcanic eruption recent 20 Structure • 19 218 INDEX. Paga Wasatch Mountains White Cliff Gronp, Distribution of 151 , relations - 18 , Sections of 53, lo%i , typo locality -r>l White, Dr. C. A., report on invertebrate paleontology of the Plateau Province 71 Yampa district 14*> River n Plateau, Structure of 202 '- •n a _o "Si o g 43 — o a ~r a CO 1 X ■/.■ 01 o> — M «) O - ■- P< 43 Cl «4-T *■* Tt JS co CD -u c Q 13 S 13 -a 13 CJ • ». cS 03 a **4 r> T3 cS 13 ■-*- .3 izz +J a. «w s O u-j o 5j (C m 1) 0) ^3 w -*-* CO CD J ■M -M cs CO X o J CO C •— ~*- CS a J £ 13 X o a o> — tl ■f 0) .3 is t-i X W 0) 4^ > 13 0 CS 03 CO o 03 -s s CS CO 3 1~ 3S ■2 fcJO O CJ O) CO 13 till s Ph O 01 11 CO — MJ t^ S3 ^-^ Ch cS K ;jc H | =3 0 u +- H "~ O *- ~ W t<- — Ph C9 co u i— cc H CS 3 » p2 4— O 13 ^ S - rj h f-i ■!> DEPARTMENT OF THE INTERIOR. U. S. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGDN. J. W. POWELL, in Charge. KEPORT 9?'/^- ON THE GEOLOGY OF THE HENRY MOUNTAINS. By G. K. GILBERT WASHINGTON: GOVERNMENT PRINTING OFFICE. 1877. v> Department of the Interior, U. S. Geographical and Geological Survey of the Rocky Mountain Region, Washington, D. C, March 5, 1877. Sir : I have the honor to transmit herewith a report on the Geology of the Henry Mountains, by Mr. G. K. Gilbert. I am, with great respect, your obedient servant, J. W. POWELL, In charge. The Hon. Secretary of the Interior, Washington, D. G. rn-rv Department of the Interior, U. S. Geographical and Geological Survey of the Rocky Mountain Region, Washington, D. C, March 1, 1877. Dear Sir : I submit herewith my report on the Geology of the Henry Mountains, prepared from material gathered under your direction in the years 1875 and 1876. I am, with great respect, your obedient servant, G. K. GILBERT. Prof. J. W. Powell, In charge. r-VT PREFACE. If these pages fail to give a correct account of the structure of the Henry Mountains the fault is mine and I have no excuse. In all the earlier exploration of the Rocky Mountain Region, as well as in much of the more recent survey, the geologist has merely accompanied the geographer and has had no voice in the determination of either the route or the rate of travel. When the structure of a mountain was in doubt he was rarely able to visit the points which should resolve the doubt, but was compelled to turn regretfully away. Not so in the survey of the Henry Mountains. Geological exploration had shown that they were well disposed for exam- ination, and that they promised to give the key to a type of structure which was at best obscurely known ; and I was sent by Professor Powell to make a study of them, without restriction as to my order or method. I was lim- ited only in time, the snow stopping my work two months after it was begun. Two months would be far too short a period in which to survey a thousand square miles in Pennsylvania or Illinois, "but among the Colorado Plateaus it proved sufficient. A few comprehensive views from mountain tops gave the general distribution of the formations, and the remainder of the time was spent in the examination of the localities which best displayed the peculiar features of the structure. So thorough was the display and so satisfactory the examination, that in preparing my report I have felt less than ever before the desire to revisit the field and prove my conclusions by more extended observation. In the description of the details of the structure a demand arose for a greater number of geographic titles than were readily suggested by nat- ural forms or other accidents, and recourse was had to the names of geolo- gists. Except that the present members of my own corps are not included, the names chosen are of those whose cognate studies have given me most aid. Mr. Steward and Mr. Howell saw the Henry Mountains before I did, VII viii PREFACE. and gleaned something of their structure from a distance ; Dr. Newberry, Mr. Marvine, Dr. Peale, and Mr. Holmes have described allied phenomena in Colorado and New Mexico ; and the works of Messrs. Jukes, Geikie, Scrope, and Dana have been among my chief sources of information in regard to igneous mountains in general. If any of these gentlemen feel offended that their names have been attached to natural features so insig- nificant, I can assure them that the affront will never be repeated by the future denizens of the region. The herders who build their hut at the base of the Newberry Arch are sure to call it " the Cedar Knoll"; the Jukes Butte will be dubbed "Pilot Knob", and the Scrope, "Rocky Point". During the preparation of my report every part of the discussion has been submitted to Professor Powell for criticism, and many of his sugges- tions are embodied in the text. Similar and valuable aid was received from Capt. C. E. Dutton and Mr. William B. Taylor in the stud}r of the physical problems to which the discussion of the intrusive phenomena gave rise. Captain Dutton rendered an important service also by the study of the collection of igneous rocks, and his report, included in the fourth chap- ter, testifies to the thoroughness of his work. The supervision of the pub- lication has fallen in large share upon Mr. J. C. Pilling, and the text has had the advantage of his literary criticism, as well as of his watchful care. G. K. G. CONTENTS. Page. Chapter I. Introductory 1 The rock series 3 Unconformities 8 The Great Folds 11 Cliffs and plateaus 13 How to reach tbe Henry Mountains 14 Chapter II. Structure of the Henry Mountains 18 Chapter III. Detailed description of the mountains 22 Mount Ellsworth , 22 Mount Holmes 27 Mount Hillers 30 Mount Pennell 35 Mount Ellen , 38 Stereogram of the Henry Mountains 49 Chapter IV. The Laccolite 51 The Henry Mountains intrusives, by Captain C. E. Duiton 4#~ The question of cause 72 The stretching of strata 80 The conditions of rock flexure 83 The question of cover and the question of age 84 The history of the laccolite 95 Laccolites of other regions 97 Possible analogues of the laccolite 98 Chapter V. Land sculpture 99 I. Erosion „ 99 A. Processes of erosion 99 Weathering 100 Transportation 101 Corrasion 101 B. Conditions controlling erosion 102 Rate of erosion and declivity 102 Rate of erosion and rock texture 103 Rate of erosion and climate 103 Transportation and comminution 106 Transportation and declivity 108 Transportation and quantity of water 109 Corrasion and transportation Ill Corrasion and declivity 112 Declivity and quantity of water 113 II. Sculpture 115 Sculpture and declivity 115 The law of structure 115 The law of divides 116 Sculpture and climate 117 Bad-lands 120 Equal action and interdependence 123 IX U X CONTENTS. Chapter V. Land sculpture — Continued. III. Systems of drainage 124 The stability of drainage lines 124 The instability of drainage lines 125 The stability of divides 138 The instability of divides 139 Consequent and inconsequent drainage 143 The drainage of the Henry Mountains 144 Chapter VI. Economic 151 CHAPTER I. INTRODUCTORY. The Henry Mountains have been visited only by the explorer. Pre- vious to 1869 they were not placed upon any map, nor was mention made of them in any of the published accounts of exploration or survey in the Rocky Mountain region. In that year Professor Powell while descending the Colorado River in boats passed near their' foot, and gave to them the name which they bear in honor of Prof. Joseph Henry, the distinguished physicist In 1872 Prof. A. H. Thompson, engaged in the continuance of the survey of the river, led a party across the mountains by the Penellen Pass, and climbed some of the highest peaks. Frontiersmen in search of farming and grazing lands or of the precious metals have since that time paid several visits to the mountains; but no survey was made of them until the years 1875 and 1876, when Mr. Walter H. Graves and the writer visited them for that purpose. They are situated in Southern Utah, and are crossed by the meridian of 110° 45' and the thirty-eighth parallel. They stand upon the right bank of. the Colorado River of the West, and between its tributaries, the Dirty Devil and the Escalante. At the time of their discovery by Professor Powell the mountains were in the center of the largest unexplored district in the territory of the United States — a district which by its peculiar ruggedness had turned aside all previous travelers. Up to that time the greater part of the knowledge that had been gained of the interior of the continent had been acquired in the search for routes for transcontinental railways; and the canons of the Colo- rado Basin, opposing more serious obstacles to travel than the mountain ranges which were met in other latitudes, were by common consent avoided by the engineers. 1 II M 2 INTRODUCTORY. *■ -*. The same general causes which have rendered the region so difficult of access and passage* have made it a desert, almost without economic value. The physical conditions of elevation and aridity which have caused it to he so deeply carved in canons, have prevented the streams with which it is scantily watered from being bordered by tracts of land which can be irri- gated; and agriculture without irrigation being in that climate an impossi- bility, there is nothing to attract the farmer. As will be explained in the sequel, the mountains offer no inducements to the miner of the precious metals. There is timber upon their flanks and there is coal near at hand, but both are too far removed from other economic interests to find the mar- ket which would give them value. It is only for purposes of grazing that they can be said to have a money value, and so distant are they at present from any market that even that value is small. But while the Henry Mountains contribute almost nothing to our direct material interests, they offer in common with the plateaus which surround them a field of surpassing interest to the student of structural geology. The deep carving of the land which renders it so inhospitable to the traveler and the settler, is to the geologist a dissection which lays bare the very anatomy of the rocks, and the dry climate which makes the region a naked desert, soilless and almost plantless, perfects the preparation for his exami- nation. The study of the mountains is further facilitated by their isolation. They mark a limited system of disturbances, which interrupt a region of geological calm, and structurally, as well as topographically, stand by them- selves. The Henry Mountains are not a range, and have no trend; they are simply a group of five individual mountains, separated by low passes and arranged without discernible system. The highest rise about 5,000 feet above the plateau at their base and 11,000 feet above the level of the ocean. Projecting so far above the surface of the desert, they act as local con- densers of moisture, and receive a comparatively generous supply of rain. Springs abound upon their flanks, and their upper slopes are clothed with a luxuriant herbage and with groves of timber. The smaller mountains and the foot-hills of the larger are less generously watered and but scantily I1EIGIITS AND FORMS. 3 clothed with vegetation. Their extent is small. From Ellen Peak to Mount Ellsworth, the two summits which are the most widely separated, the dis- tance is but twenty-eight miles, and a circle of eighteen miles radius will include the whole group. Mount Ellen which is the most northerly of the group, has an extreme altitude of 11,250 feet, and surpasses all its companions in horizontal extent as well as altitude. Its crest-line is continuous for two miles, with an ele- vation varying little from 11,000 feet. From it there radiate spurs in all directions, descending to a series of foot-hills as conspicuous in their topography as they are interesting in their structure. In some places the base of the mountain is guarded by a continuous, steep ridge, through which a passage must be sought by the approaching traveler, but within which movement in any direction is comparatively unimpeded. Mount Pennell is a single peak rising to an altitude of 11,150 feet. On one side its slopes join those of Mount Ellen in Pennellen Pass (7,550 feet), and on the other those of Mount Hillers in the Dinah Creek Pass (7,300 feet). Its profiles are simple, and it lacks the salient spurs that characterize Mount Ellen. From the west it is difficult of approach, being- guarded by a barrier ridge continuous with that of Mount Ellen. Mount Hillers is more rugged in its character, and although compact in its general form, is carved in deep gorges and massive spurs. Its rugosity is contrasted by the smoothness of its pedestal, which to the south and west and north is a sloping plain merging with the surrounding plateau. Mount Ellsworth (8,000 feet) and Mount Holmes (7,750 feet) stand close together, but at a little distance from the others. The pass which separates them from Mount Hillers has an altitude of 5,250 feet. They are single peaks, peculiarly rugged in their forms, and unwatered by springs. They stand almost upon the brink of the Colorado, which here flows through a canon 1,500 feet in depth. THE ROCK SERIES. The sedimentary rocks which occur in the Henry Mountains and their immediate vicinity, range from the summit of the Cretaceous to the summit of the Carboniferous. It is probable that they were covered at one time 4 INTRODUCTORY. by some thousands of feet of Tertiary strata, but from the immediate banks of the Colorado these have been entirely eroded, and their nearest vestiges lie thirty miles to the westward, where they have been protected by the lava-beds of the Aquarius Plateau. Cretaceous. — The Cretaceous strata do not reach to the Colorado River, but they extend to the Henry Mountains, and are well displayed upon the flanks. They include four principal sandstones, with intervening shales, in the following (descending) order : 1 . The Ma-suk' Sandstone, yellow, heavy-bedded 500 feet. 2. The Ma-suk' Shale, gray, argillaceous, and toward the top slightly arenaceous 500 feet. 3. The Blue Gate Sandstone, yellow and heavy-bedded 500 feet. 4. The Blue Gate Shale, blue-black and argillaceous, weather- ing to a fine gray clay {Inoceramus deformis and I. prob- lematicus) 1 , 000 feet. 5. The Tu-nunk' Sandstone, yellow and heavy-bedded 100 feet. 6. The Tu-nunk' Shale, blue-black and argillaceous, weather- ing 'to a fine gray clay {Inoceramus problematicus and Ba- culites anceps) 400 feet. 7. The Henry's Fork Group, consisting of — a. Friable yellow sandstone with numerous fossils (Ostrea prudentia, Gryphea Pitcheri, Exogyra Iceviuscula, Exo- gyra ponderosa, Plicatula Jiydrothcca, Camptonectes pla- tessa, and Callista Deweyi) 10 feet. b. Arenaceous shales, purple, green, and white, with local beds of conglomerate- ." , 190 feet c. Coarse sandstone and conglomerate, with many white grains and pebbles, interleaved with local beds of purple and red shale, and containing immense silici- fied tree-trunks 300 feet. Total Cretaceous 3, 500 feet. The three upper sandstones, the Masuk, the "Blue Gate, and the Tu- nunk, are so nearly identical in their lithologic characters that I was unable CRETACEOUS ROCKS. 5 to discriminate them in localities where their sequence was unknown. This was especially the case upon the summits of Mounts Ellen and Pennell where they occur in a somewhat metamorphosed condition. All of them contain thin beds of coal, none of which are continuous over large areas, and only one of which was observed of workable thickness. At the western foot of Mount Ellen, a bed four feet thick lies at the base of the Blue Gate Sandstone. There is almost equal difficulty in discriminating- the Masuk, the Blue Gate, and the Tununk shales. The first is usually of a paler color and is more apt to include arenaceous bands. It has not been found to contain fossils, while the lower shales rarely fail to afford them when search is made. The Blue Gate and Tununk shales are typical examples of fine argillaceous sediments. They are beautifully laminated and are remarkably homoge- neous. It is only in fresh escarpments that the lamination is seen, the weathered surface presenting a structureless clay. The fossils of these shales are so numerous, when they have been sought out and studied, that they will probably serve not merely to discriminate the two, but also to correlate them with some of the beds which have been examined elsewhere in the Colorado Basin. For the present I am unable to refer any of the Cretaceous rocks above the Henry's Fork Group to the divisions which have been rec- ognized elsewhere, and it is for this reason that I have given local, and perhaps temporary names to such beds as I have need to mention in the discussion of the structure of the mountains. The fossils of the Henry's Fork Group have been mere fully collected, and they have been referred without question by Dr. White to the group of that name, as recognized in the Green River Basin (Geology of the Uinta Mountains, pp. 82 and 94). The white grit which lies at the base of the group is a conspicuous bed of unusual persistence, and is recognized wherever Cretaceous rocks are found in the upper basin of the Colorado. Jura-Trias. — The rocks which intervene between the base of the Cre- taceous and the summit of the Carboniferous are of doubtful age, having been referred to the Trias by one geologist and to the Jura and Trias by others, while the fossils recently discovered by Mr. Howell (Geology of Uinta Mountains, page 80) lead to the suspicion at least that they are all 6 Introductory. Jurassic. It is probable that the uncertainty will soon be dispelled by the more thorough working of Mr. Howell's new localities ; but while it re- mains, it seems best to recognize its existence in our nomenclature, and I shall include the whole of the doubtful series under the title of Jura-Trias. At the Henry Mountains it is easily divided into four groups, as follows : 1. Flaming Gorge Group ; arenaceous shales or bad-land sand- stones, purple and white at top and red below 1, 200 feet. 2. Gray Cliff Group ; massive cross-laminated sandstone, buff to red in color 500 feet. 3. Vermilion Cliff Group ; massive cross-laminated sandstone, red, with a purple band at the top 500 feet. 4. Shin-ar'-ump Group ; consisting of — a. Variegated clay shale ; purple and white above and chocolate below, with silicified wood 300 feet. 1). Gray conglomerate, with silicified wood ; the " Shin- arump Conglomerate " 30 feet. c. Chocolate-colored shale, in part sandy 400 feet. Total Jura-Trias 2, 930 feet. The rock of the Flaming Gorge Group is of a peculiar character. It is ordinarily so soft that in its manner of weathering it appears to be a shale. It is eroded so much more rapidly than the Henry's Fork conglomerate above it, that the latter is undermined, and always appears in the topography as the cap of a cliff. Nevertheless, it is not strictly speaking a shale. The chief product of its weathering is sand, and wherever it can be examined in an unweathered condition it is found to be a fine-grained sandstone, massive and cross-laminated like those of the Gray and Vermilion Cliffs, but devoid of a firm cement. In a number of localities it has acquired, locally and accidentally, a cement, and it is there hardly distinguishable from the firmer sandstones which underlie it. In the immediate vicinity of the Henry Mountains it varies little except in color from summit to base, but in other localities not far distant it is interrupted near the base by thick beds of gypsum and gypsiferous clays, and by a sectile, fossiliferous lime- stone. JUKA-TU1AS EOCKB. 7 Tlie Gray Cliff and Vermilion Cliff sandstones are often difficult to distinguish, but the latter is usually the firmer, standing in bold relief in the topography, with level top, and at its edge a precipitous face. The for- mer is apt to weather into a wilderness of dome-like pinnacles, so steep- sided that they cannot often be scaled by the experienced mountaineer, and separated by narrow clefts which are equally impassable. The colors of the two sandstones are not invariable. The lower, which although not reddened throughout its mass is usually stained upon its surface with a uniform deep color, appears in Mount Ellsworth and at other points of elevation with as pale a tint as that of the Gray Cliff. The latter sand- stone, on the other hand, where it lies low, is often as deep in color as the Vermilion. Standing upon one of the summits of the Henry Mountains and looking eastward, I found myself unable to distinguish the Gray Cliff Sand- stone by color either from the lower part of the Flaming Gorge Group or from the Vermilion Sandstone. The bleaching of the redder sandstone in Mount Ellsworth is probably a result of metamorphism ; the reddening of the gray sandstone may depend on the hydration of the iron which it con- tains. The thickness of individual strata in these great sandstones is remark- able, and is one of the elements which must be taken into account in the discussion of the problem — which to my mind is yet unsolved — of the man- ner in which such immense quantities of homogeneous sand were accumu- lated. Ordinarily the depth of strata is indefinable, on account of the im- possibility of distinguishing stratification from lamination; but where, as in this case, the lamination is oblique to the stratification, the upper and lower limits of each stratum are definitely marked. I have at several points measured single strata with thicknesses of about fifty feet, and near Water- pocket Canon a stratum of Vermilion Cliff sandstone was found to be 105 feet thick. One other measurement is worthy of record; the inclination which oblique lamination bears to the plane of the stratum in which it occurs appears to have a definite limit. The maximum of a series of measurements made at points where to the eye the dip seemed to be unusually great, is 24°. 8 INTRODUCTORY. The sandy layers at the base of the Shinarump Group are character- ized by profuse ripple- marks. Carboniferous. — Beneath the Jura-Trias is the Carboniferous. A few hundred feet of its upper member, the Aubrey Sandstone, are exposed near the summit of Mount Ellsworth. At that point the sandstone is altered to the condition of a quartzite, but where it is cut by the upper and lower canons of the Dirty Devil River it is massive and cross-laminated, differing" from the Gray Cliff sandstone chiefly in the abundance of its calcareous cement UNCONFORMITIES. From the Masuk Sandstone to the Aubrey Sandstone, inclusive, there is perfect conformity of dip. The fold system of the region, of which a description will be found in succeeding pages, was established after the deposition of all these strata, and the whole series were flexed together. Nevertheless, the strata do not represent continuous deposition. There were intervals in which the sea receded and exposed to erosion the sedi- ments which it had accumulated. Shallow valleys and water-ways were excavated, and when the sea returned it deposited new sediments upon the somewhat uneven surface of the old. The first occurrence of this sort was at the close of the Aubrey epoch. Its evidence was not found in the Henry Mountains; but at the con- fluence of the Paria with the Colorado, eighty miles to the southeast, the surface of the upper member of the Aubrey Group, which is there a cherty limestone, is unevenly worn, and in its depressions are beds of conglomer- ate, the pebbles of which are derived from the chert of the limestone itself. The shaly, rippled sandstones which succeed this conglomerate indicate that the water remained shallow for a time, and in the middle of the Shin- arump epoch the region was once more abandoned by the sea. The choco- late shales and shaly sands were unevenly worn, and the first deposit that the returning sea spread over them was a conglomerate. The evidence of this break is found at many points. The Shinarump conglomerate although remarkably persistent for a conglomerate thins out and disappears at a number of points, and at the margins of its areas it is evident to the eye that it occupies depressions of the surface on which it rests UNCONFORMITIES. The next break is at the base of the Vermilion Cliff Group. In the region of the Virgin River and Kanab Creek the change from the va- riegated shales of the Upper Shinarump to the homogeneous sandstone of the Vermilion Cliff is gradual, the interval being filled by a series of alternating shales and sandstones; but further to the east, in the region of the Henry Mountains and Waterpocket Canon, the change is abrupt, and the firm sandstone rests directly upon the soft shale. The abruptness of the change would suggest that the currents which brought the sand had swept away all evidence of the intermediate conditions which are likely to have connected the epochs represented by the two sediments ; but in one locality, at least, there is direct evidence that the surface of the clay was exposed to the air before it was covered by the sand. On the northern flank of Mount Ellsworth are the vestiges of a system of mud-cracks, such as form Fig. 1.— Fossil Suncracks in the Shinarump Shale. where wet clays are dried in the sun. Where the under surface of the Vermilion sandstone is exposed to view, it is seen to be marked by a net- work of ridges which once occupied the sun-cracks of the Shinarump clay; and where the clay is seen in juxtaposition, tapering fillets of sand can be traced from the ridges downward ten feet into the clay. 10 INTKODUCTOKY. From the base of the Vermilion to the summit of the Cretaceous no evidence of land erosion has been found ; but the association of coal seams with all of the Cretaceous sandstones except the lowest, shows that the sea- bottom was frequently brought to the surface of the water if it was not carried above. Thus it is evident that the strata of the Henry Mountain region do not represent continuous sedimentation. At the close of the Aubrey epoch, in the middle of the Shinarump, and again at the close of the Shinarump, not merel}7 was the accumulation of sediments interrupted, but the process was reversed, and a portion of the deposits which had already been formed were excavated by the agency of rains and rivers, and swept away to some other region. Each break is indefinite, alike as regards the interval during which the record of the sea was interrupted and as regards the extent of the record which was at the same time obliterated. And yet the evidence of these breaks is of such nature that it would probably elude observation if a single section only were examined, and in a region masked by the soil and vegetation of a humid climate it would hardly be discovered except by accident. The parallelism of contiguous strata is not alone sufficient evi- dence that they were consecutive in time. At the close of the Cretaceous period there came an epoch of disturb- ance. The system of strata which has been described was bent into great waves, and the crests of the waves were lifted so high above the sea that they lost thousands of feet by erosion. In the troughs between the waves lakes remained, in which the mate- rial removed from the crests was redeposited, and by a later change the lake waters rose so as to cover the truncated crests, and deposit upon the worn edges of the upbent strata a series of unconforming, fresh-water, Ter- tiary sediments. Thus was produced the only unconformity of dip which involves the Henry Mountain rocks, and even this is not to be observed in the immediate vicinity of the mountains, for a later erosion has thence removed all of the Tertiary strata, and has resumed the degradation of the older beds. DISPLACEMENTS. 1 1 THE GREAT FOLDS. The disturbances at the close of the Cretaceous period were of the Kaibab type*. It seems as though the crust of the earth had been divided into great blocks, each many miles in extent, which were moved from their original positions in various ways. Some were carried up and others down, and the majority were left higher at one margin than at the other. But although they moved independently, they were not cleft asunder. The strata remained continuous, and were flexed instead of faulted at the mar- gins of the blocks. Subsequent erosion has obliterated in great part the inequality of the surface, and the higher-lying blocks do not stand as mount- ains, but are outlined by zones of tilted strata which mark the flexures by which the blocks are separated. Along the zones of flexure it frequently happens that a hard stratum outcropping between two that are softer will be preserved from erosion and form a long, continuous ridge. Such ridges, and other forms produced by the erosion of the flexures, are conspicuous features of the topography, and the tracing out of the limits of the blocks is a simple matter. Indeed the flexures are the first elements of the structure to attract attention, and it is easy in studying them to overlook the fact that they merely mark the limits between displaced masses of great extent. If the reader will examine Plate I at the end of the volume, he will observe that the system of parallel ridges and valleys which follow the line of the Waterpocket flexure are very conspicuous features ; but it is only by some such generalization as that given in the stereogram of the same region (Plate II) that the full structural significance of the flexures can be realized. Each map was obtained by photography from a model in relief, in which the proportionate heights of the several features were not exaggerated. ( The stereogram was produced by the restoration of the top of the Cretaceous, the Masuk sandstone, in the form and position it would have, had there been no .erosion of the region, but displacement only. I must caution the reader against an implication of rigidity which might attach to the meaning of the word "block", as I have used it in speaking *For a definition of the Kaibab structure, see "Geology of the Uiuta Mount- ains," pp. 14 aud 17, and American Journal of Science for July and August, 1876, pp. 21 aud 85. 12 INTRODUCTORY. of the great displaced rock-masses. To what extent they may be regarded as rigid is uncertain, but the presence upon their surfaces of numerous minor flexures, such as appear in the stereogram, would seem to imply that their rigidity is not of a high order. In the northwest corner of the area represented by the stereogram are a few faults belonging to a system which occupies a large area in that direction. The system of faults and the system of flexures are inde- pendent, the latter having originated at the close of the Cretaceous period, and the former after the formation of the Tertiary rocks of the region, which are referred by Professor Powell to the Bitter Creek epoch. Over a large district the Tertiary strata were covered by a deep mantle of lava, which has protected them from erosion to such an extent that the structure of the district is portrayed in its topography. The district is its own stereo- gram, each uplifted block constituting" a mountain and each depressed block flooring a valley. Not all the displacements of the later system are by faulting, but by far the greater number. Of the earlier system of displacements none are simple faults, but a few are combinations of fault and flexure. 14 13 Fig. 2. — Cross-section of the Waterpocket Flexure, opposite the Masnk Plateau. Scale, one inch = 3,r,00 feet. l,Masuk Sandstone. 2, Masuk Shale. 3, Blue Gate Sandstone. 4, Blue Gate Shale. 5,Tununk Sandstone. 6, Tuuunk Shale. o.Grypkea Sandstone. 7, Henry's Fork Conglomerate. 8, Flaming Gorge Shale. 9, Fossiliferous Limestone. 10, Gray Cliff Sandstone. 11, Vermilion Cliff Sandstone. 12, Upper Shiuarump Shale. 13, Shinarump Conglomerate. 14, Lower Shinarump Shale. 15, Auhrey Sandstone. The Waterpocket flexure, represented in the stereogram (Plate II), is better known in detail than any other of the great flexures of Southern Utah. It is far from following a straight line, but like most lines of oro- u a o O M S-, O En _75 >* — a ID w D A *- >. ,J2 a : | o -»^ x> 33 Z- rs z_ a ■r. c3 o t» I fc! 42 p^ I. o d "- o ■g s "* — * > o -a i B eS r^ >3 -- — £ o — z V X ^2 b ■*J Ed S -U 5 3 be f3y M I a) 43 J3 o9 -w £ c3 d in — ^ *• o r_ O X - -; T3 £1 3 J3 u in s- c^ cS O They are J^.. gest and most numerous about the center, but, like the superior sheets, they often extend nearly to the limit of the flexure of the uplifted strata. The larger often radiate from the center outward, but there is no constancy of arrangement. Where they are numerous they reticulate. In the accompanying diagrams dikes are represented beneath as well as above the laccolites. These are purely hypothetical, since they have not been seen. In a general way, the molten rock must have come from below, but the channel by which it rose has in no instance been determined by observation. The horizontal distribution of the laccolites is as irregular as the arrange- merit of volcanic vents. They lie in clusters, and each cluster is marked DIKES AND SHEETS. 21 by a mountain. In Mount Ellen there are perhaps thirty laccolites. In Mount Holmes there are two; and in Mount Ellsworth one. Mount Pen- nell and Mount Hillers each have one large and several smaller ones. Their vertical distribution likewise is irregular. Some have intruded themselves between Cretaceous strata, others between Jura-Triassic, and others between Carboniferous. From •the hisrhest to the lowest the range is not less than 4,000 feet. Those which are above not unfrequently overlap those which lie below, as represented in the ideal section, Figure 10. Fig. 10.— Ideal Cross-section of Grouped Laccolites. The erosion of the mountains lias given the utmost variety of exposure to the laccolites. In one place are seen only arching strata; in another, arching strata crossed by a few dikes; in another, arching strata filled with a net-work of dikes and sheets. Else- where a portion of the laccolite itself is bared, or one side is removed so as to exhibit a natural section. Here the sedimentary cover has all been re- moved, and the laccolite stands free, with its original form; there the hard trachyte itself has been attacked by the elements and its form is changed. Somewhere, perhaps, the laccolite has been destroyed and only a dike re- mains to mark the fissure through which it was injected CHAPTER III. DETAILED DESCRIPTION OF THE MOUNTAINS. MOUNT ELLSWORTH. It has already been stated that the strata about the bases of the Henry Mountains are nearly level; but the country which is built of them is far from level. The arrangement of the drainage lines has caused the degra- dation of some parts to greatly exceed that of others, so that while the dis- trict at the south, which borders the Colorado River, is paved with the red sandstones of the Jura-Trias series, the adjacent region at the north still carries the yellow sandstones and blue shales of the Cretaceous series. All about Mount Ellsworth are the upper strata of the Jura-Trias. The lower beds of the same series rise upon its flanks and arch over its summit. A description of the structure of the mountain must include, first, the arch of the strata ; second, the faults which modify the arch ; third, the system of tra- chyte dikes and trachyte sheets; and fourth, the sculpture#of the mountain. In its general proportions the arch is at once simple and symmetrical. From all sides the strata rise, slowly at first, but with steadily increasing rate, until the angle of 45° is reached. Then the dip as steadily diminishes to the center, where it is nothing. A model to exhibit the form of the dome would resem- ble a round-topped hat; only the level rim would join the side by a curve in- stead of an angle, and the sides would not be perpendicular, but would flare rapidly outward (see Figure 11). The base of the arch is not circular, but is slightly oval, the long diameter being one-third greater than the short. The length of the uplift is a little more than four miles ; the width a little more than three miles, and the height about 5,000 feet. The curvature fades away so gradually at its outer limit that it is not easy to tell where it ends, and the horizontal dimensions assigned to the dome are no more than rude approxi- mations. But there is another element which can be given more exactly. 22 MOUNT ELLSWORTH. 23 The line of maximum dip, which separates the convex upper portion of the dome from the concave periphery, is easily traced out in nature, and runs at the foot of the steep part of the mountain. It surrounds an area two miles in width and two and two-thirds miles in length. Fig. 11. — Stereogram of Mouut Ellsworth ; an ideal restoration of the form of the overarching strata. The Ellsworth arch is almost but not completely isolated. The Holmes arch, upon the east side, stands so near that the bases of the two impinge and coalesce, and the same tiling happens, though less notably, with the Hillers arch at the north. The simplicity of the arch is further impaired by faults — not great faults dividing the whole uplift, but a system of small displacements which are themselves subordinate phenomena of the uplift. They are restricted to the central portion, and never occur so low down as the line of maximum dip. The strata of the upper part of the arch are divided into a number of prismoid blocks which stand at slightly different levels but are not suffi- ciently deranged to destroy the general form of the arch. The greatest throw is only a few hundred feet. All or nearly all of the fault planes are occupied by dikes of trachyte. The trachyte injections are not confined to the fault planes, nor is their area so restricted as the fault area. Dikes and sheets abound from the crest of the dome down to what might be called its springing line — the line of maximum dip. At the center, dikes are more numerous ; near the limit, sheets. The central area is crowded so full of dikes, and the weathering brings them so conspicuously to the surface, that the softer sedimentaries are half concealed, and from some points of view the trachyte appears to make the entire mass. The accompanying plat (Figure 12) shows the arrange- 24 DETAILED DESCRIPTION. ment of the dikes in one of the outer amphitheaters of the mountain, where they are less complicated than in the central region. The trends of two spurs (a b and c d) are indicated by the hatchings. They join the main crest of the mountain at e, and inclose between them a deep amphitheater which opens to the west. Upon the steep walls of the amphitheater the dikes outcrop in lines of crags, dividing rough slopes of yellow and purple and brown sandstone. The profile of one of the walls of the amphitheater (from a to 6, Figure 12) is drawn in Figure 13 for the sake of exhibiting the relation of the dikes to faulted blocks of sandstone. It will be seen that the throw of the faults is not constantly in one direction. The zone of sheets is just inside the line of maximum dip. Usually Fig. 14. — Profile of the Northern Spur of Mount Ellsworth. 1, 2, 3, 4, and 5 are Trachyte Dikes. A, Aubrey Sandstone. S, Shinarump Shale. V, Vermilion Cliff Sandstone. G, Gray Cliff Sandstone. only one or two sheets are laid bare by the erosion, but at one point (see Figure 14) four can be counted. Toward the center of the uplift all of these are limited by the erosion and exhibit their broken edges. Down- ward, or toward the periphery, they dip out of sight. Laterally they can be traced along the mountain side for varying distances, but they soon wedge out and are replaced by others en echelon. In thickness the sheets rarely exceed 50 feet, and never 100. They are always thin as compared to the rock masses which separate them, but, by reason of their superior ability to resist erosion, monopolize a large share of the surface, and mask a still greater amount with their debris. The sedimentary rocks are not altered beyond the region of trachyte intrusion. The mere flexure of the strata was not accompanied by a per- ceptible change of constitution. In the zone of sheets there is little change except along the surfaces of the contact. For a few feet, or perhaps only y 0f~o ^^^'''/////''/-v'UI'''''''///||l^llUU"""""'"'vllV Fig. 12. — Grouud plan of Trachyte Dikes on the western flank of Mount Ellsworth. Fig. 13. — Profile of a wesleru spur of Mount Ellsworth, showing tlfe arrangement of Dikes and Faults, The dotted hed is the purple band at the top of the Vermilion Cliff Sandstone. The dikes of trachyte are indicated by letters. TflE ZONE OF SBEETS. 25 a few inches, there is a discoloration (usually a decolorization) and a slight induration, without notable alteration of minerals. But in the region of reticulated dikes none of the sedimentaries are unchanged ; crystals are de- veloped, colors are modified, and hardness is increased, so that the physical properties of familiar strata no longer serve for their identification. Still there is no crumpling. The trachyte masses and the altered rocks in contact with them are so much more durable than the unaltered strata about them that they have been left by the erosion in protuberences. The outcrop of every dike and sheet is a crag or a ridge, and the mountain itself survives the general degradation of the country only in virtue of its firmer rock masses. Never- theless, the mountain, because it was higher than its surroundings, has been exposed to more rapid erosion, and has been deprived of a greater depth of strata. From the base of the arch there have been worn 3,500 feet of Cretaceous, and from 500 to 1,500 feet of the Jura-Trias series, which is here about 3,000 feet thick. From the summit of the arch more than 2,500 feet of the Jura-Trias have been removed. The strata exposed high up on the mountain being older than those at the base, and the dip being everywhere directed away from the center, it is evident that the mountain is surrounded by concentric outcrops of beds which lift their escarpments toward it. It is usually the case, where the strata which incline against the flank of a mountain are eroded, that the softer are excavated the more rapidly, while the harder are left standing in ridges ; and an alternation of beds suitable for the formation of a ridge occurs here. One of the upturned beds is the massive Vermilion Cliff sandstone, and beneath it are the shales of the Shinarump Group. By the yielding of the shales the sandstone is left prominent, and it circles the base of the mountain in a monoclinal ridge. But the ridge is of a peculiar character, and has really no title to the name except in the homology of its structure with that of the typical monoclinal ridge. It lacks the continuity which is implied by the word " ridge". The drainage of Mount Ellsworth is from the center of the dome outward. A half dozen drainage-lines originate in the high crests and pass outward through the zone of upturned strata. Lower down their interspaces are divided by others, and • 20 DETAILED DESCRIPTION. when they reach the circling escarpment of the Vermilion sandstone their number is fifteen. Each of these cuts the ridge to its base, and the effecl of the whole is to reduce it to a row of sandstone points circling about the mountain. Each point of sandstone lies against the foot of a mountain spur, as though it had been built for a retaining wall to resist the out-thrust of the spur. Borrowing a name from the analogy, I shall call these element- ary ridges revet-crags, and speak of the spurs which bear them as being revetted. The accompanying sketch is designed to illustrate the structure, but is not drawn from nature. In the view of Mount Hillers (Figure 27) the revetments may be seen, and in the bird's-eye view of the Henry Mountains (Plate V), as well as in the Frontispiece, the revet-crags of Mount Ellsworth also are portrayed. The diagram of the north spur of Mount Ellsworth (Figure 14) shows the revet-crag of that spur at V. Fig. 15. — Kevet-Crags. The revet-crags of Vermilion sandstone follow, in a general way, the line of maximum dip about the base of Mount Ellsworth; but a few of them rise higher, and one — that which joins the northwest spur— climbs until it is but little lower than the summit of the mountain. Outside the circle of Vermilion Cliff sandstone lies the Gray Cliff sandstone, and in a few places it takes the form of a revetment. Inside the same circle there are many revetments, constituted by trachyte sheets bedded in Shinarump shales (Figure 14). Conforming perfectly with the strata, the sheets yield by erosion forms which are identical with those afforded by hard sedimentary beds, and to the distant eye the impression of the arching structure of Mount Ellsworth is conveyed less by what can be seen of the strata than by as- cending revetments of trachyte sheets, which simulate and interpret the strata. X V a o K MOUNT HOLMES. 27 The laccolite of Mount Ellsworth is not exposed to view, but I am nevertheless confident of its existence — that the visible arching strata envelop it, that the visible forest of dikes join it, and that the visible faulted blocks of the upper mountain achieved their displacement while floated by the still liquid lava. The proof, however, is not in the mountain itself, but depends on the association of the phenomena of curvature and dike and sheet with laccolites, in other mountains of the same group. In the sequel these will be described, but it chances that the mountain next to be considered is even less developed by erosion than Mount Ellsworth. MOUNT HOLMES. The order of sequence which places Mount Ellsworth before Mount Holmes is the order of complexity. The former contains one laccolite, the latter two. Neither of the two is visible, but the strata which envelop them shadow forth their forms and leave no question of their duality. They are so closely combined that the lesser seems a mere appendage of the greater. From the center of the greater there is a descent of strata in all directions, but from the center of the lesser the rocks incline toward one-half only of the horizon. Where the two convex arches join there is a curved groin — a zone of concave curvature uniting the two convexities. About the compound figure can be obscurely seen a line of maximum dip, and beyond that the fading of the curves. The curves throughout are so gentle that it was found exceedingly difficult to establish their limits. In a general wa}^ it may be said that each of the Holmes arches is as broad as the Ellsworth arch, but the vertical displacement is less. In the for- mation of the greater Holmes arch the amount of uplift was 3,000 feet; for the lesser arch, 1,500 feet. There is no evidence in the forms of the arches which proves one to be older than the other. Studying the curves in the field, I could not dis- cover that either arch asserted itself more strongly than the other in their common ground. They seem to meet upon equal terms. Still it is proba- ble, a iiriori, that they were formed successively and not simultaneously. The coincidence in time of two eruptions of lava from neighboring vents is no more unlikely than the coincidence of the two irruptions, and the same 28 DETAILED DESCRIPTION. principle of least resistance which causes individual laccolitic arches to assume spheroidal forms, would have given to the compound arch of two laccolites, coincident in time, a simple instead of a compound form. Assuming that the arches were successive in origin I shall in another and more appropriate chapter discuss the problem of their chronological order in the light of their somewhat peculiar drainage system. The lesser arch betrays no dikes nor sheets. The Vermilion Cliff sandstone covers it to the top. The greater is crowned by a few grand dikes which govern its topography. From the center a long dike runs to the south, a short one to the north, two to the east, and one to the west. The course of each is a mountain spur, and between them are am- phitheaters and gorges. Clinging to the dikes are bodies of altered sand- stone, but the great sandstone masses of the summit were unaltered and from them have been excavated the gorges. Along the dike-filled fis- sures there has been some faulting, but there is no reason to believe that the displacement is great in amount. Toward the flanks of the mountain there are a few sheets, the outermost of which is far within the line of max imum flexure. Their escarpments instead of facing upward like the revet- ting sheets of Mount Ellsworth, face downward ; their buried and unknown edges are the edges toward the mountain. Their thinning toward the periphery of the arch is conspicuous to the eye in many instances, as is also the thinning of the dikes. Another peculiarity of dike form, one which has since been noted in a number of localities, was first detected in Mount Holmes. It consists in a definite upper limit. The dike so marked is often as even upon its upper surface as an artificial stone wall. The upper surface may be level or may incline toward one end of the dike, but in either case it is sure to be found parallel to the bedding of the strata which inclose the dike. This fact led to the suspicion, afterward confirmed by more direct evidence, that the flat top of the dike was molded by an unbroken stratum of rock bridging across the fissure which the lava filled (Figure 20). The con- verse phenemenon can be observed in the ridge which joins Mounts Ells- worth and Holmes. A great dike there forms the crest of the ridge for half Fig. 17. — Stereogram of the Holmes Arches; an ideal restoration of the form of the over- arching strata. Fig. 18. — Ideal cross-section of the Laccolites of Mount Holme FiG. llJ.— A tiat- tupped dike. FLAT-TOrrED DIKES. 29 a mile, its base being buried in sandstone ; but at the end of the ridge the strata are seen to be continuous beneath it (Figure 21). Fig. 20.— Ideal Cross-section of Flat-topped Dikes; a, before denudation ; b, after denudation. PjG. 21. — Ideal Cross-section of a Flat-bottomed Dike. Fig. 22. — Diagram to illustrate a hypothetical explana- tion of Flat-edged Dikes. That a fissure several feet or several scores of feet in width should end thus abruptly, demands explanation, and the phenomena immediately concerned offer none. Nevertheless it is easy to make an assumption which if true renders both cases clear. If we assume that the fissure instead of ending at the cross- head is merely offset, and re- sumes its course beyond, and that the dike contained in it has two bodies connected by a thin sheet (Figure 22), we shall have no dif- ficulty in conceiving the erosion which will produce either of the natural appearances described. The rocks which constitute Mount Holmes are the same as those about its base. The Vermilion Cliff and Gray Cliff Sandstones alone appear in the crests. The underlying Shinarump shales are cut by the erosion at a few points only, and those are near the base. For this reason the Vermil- ion Sandstone is not undermined about the base, and the circle of revet- crags which surrounds Mount Ellsworth finds no counterpart. There are, indeed, a few revetments of Gray Cliff sandstone, but they are scattered and for the most part inconspicuous. In the general view of Mount Holmes (Figure 16), one of the main dikes crowns the nearest spur, and another the spur leading to the right. At the left are minor dikes, and high up is a trap sheet notched on its lower edge. At the left base of the mountain lies the lesser arch. 30 DETAILED DESCRIPTION". Figure 23 gives a section exhibited by one of the northward canons. It shows one of the faults of the upper part of the arch and illustrates the thinning- of the sheets as they descend. FlG. SJ3. — Section sbown in a northward canon of Mount Holmes, a, Vestige of Trachyte sheet, bbb. Tra- chyte sheets, c, Trachyte dike. 1, Gray Cliif Sandstone. 2 2, Purple Sandstoue. 3, Veiniilion Cliff Saudstone. 4,Shiuarump Shale. MOUNT HILLERS. Next in order to the north is Mount Hillers. Let it not be supposed, however, that there is discernible system in the geographic arrangement of the mountains or of the laccolites. A chart of the mountain peaks and a chart of the laccolites would alike prove intractable in the hands of those geologists who draw parallel lines through groups of volcanic vents by way of showing their trend. They are as perfectly heterotactous as they could be made by an artificial arrangement. The diagram (Figure 24) shows the relation of the laccolite groups to each other and to the meridian. The principal mountain summits are indi- cated by triangles, and the curved lines inclose areas of disturbance. Mount Hillers and its foot-hills are constituted by a group of no less than eight laccolites, and a ninth, the Howell laccolite, is conveniently classed with them, although not contiguous. The Hillers laccolite is the largest in the Henry Mountains. Its depth is about 7,000 feet, and its diameters are four miles and three and three- quarter miles. Its volume is aftout ten cubic miles. The upper half con- stitutes the mountain, the lower half the mountain's deep-laid foundation. Of the portion which is above ground, so to speak, and exposed to atmos- pheric degradation, less than one-half has been stripped of its cover of arch- arching strata. The remainder is still mantled and shielded by sedimentary beds and by many interleaved sheets of trachyte. The portion which has been uncovered is not left in its original shape, but is sculptured into alpine ■< N 3S W SEA LEVEL Fig. 25. — Cross-section of Mount Hillers. Fig. 26. — The same, with ideal representation of the underground structure. Scale, 1 inch = 4,000 feet. 1. Tnnunk Sandstone; 2. Henry's Fork Conglomerate; 3. Gray Cliff Sandstone. The full black lines represent trachyte sheets, and the broad black area the Hillers Laccolite. o to IS -3 Q gg - +3 a 3 o MOUNT UILLEKS. 31 forms and scored so deeply that not less than 1,000 feet of its mass are shown in section. All about the eroded (south) face of the mountain the base is revetted by walls of Vermilion and Gray Cliff sandstone, strength- ened by trachyte sheets. At the ex- treme south these stand nearly vertical (80°), and their inclination diminishes gradually in each direction, until at the east and west bases of the mount- ain it is not more than G0°. On the north side there are no revet-crags, and the' inclination is comparatively slight. It would appear that the lac- colite was asymmetric, and was so much steeper-sided on the south that that side suffered most rapid degrada- tion. By reference to the section (Fig- ure 25) it will be seen that the sedi- mentary strata of the north flank Stretch quite tO the Summit Of the Fig. 24.— Ground Plan of the Heury Mountains. The rrn i -i i • 1 r curved Hues show the limits of the principal dis- mountain. The same beds which form placcmeut8. the triangle8j the positions of the the revet-crags on the southern base Iuahl Peaks- N> Moimt Ellen- p> Mount Penneii. H, Mount Hillers. M, Mount Holmes. E, Mount constitute also some of the highest Ellsworth. peaks. Since these rest directly upon the laccolite, it is assumed that the next lower beds of the stratigraphic series form its floor ; and the base of the laccolite is drawn in the ideal section on the level which the Shinarump Group holds where it is unaffected by the displacements of the mountain. It is noteworthy that wherever the sedimentaries appear npon the mountain top they are highly metamorphic. But in the revet-crags there is very little alteration. Massive sandstone, divided by sheets and dikes several hundred feet in thickness, is discolored and indurated at the contact surface only, and ten feet away betrays no change. The engraving of Mount Hillers (Figure 27) exhibits the south face Scale nf Titles H 2 3 ■» 5 6 1 8 / Aiy 0 32 DETAILED DESCRIPTION. with its revet-crags and bold spurs of trap. In nature the effect is height- ened by the contrast of color, the bright red revetments being strongly relieved against the dark gray of the laccolite. The strata of the summits cannot be discriminated at a distance. They are too near the laccolite in hardness to differ from it in the style of their sculpture. Of the minor laccolites of the cluster there are three so closely joined to the chief that they merge topographically with the mountain. They are not well exposed for study. The smallest, which overlooks the pass be- tween Mount Hillers and Mount Pennell (A, Figure 28) has probably lost the whole of its cover and with it so much of its substance that the original form and surface cannot be seen. Its floor is probably the Tu- nunk sandstone. East of it and lying a little deeper in the Cretaceous series is a second laccolite (B), broader, lower, and less eroded. The third (C) joins the great one on the northeast, and is so closely united that it was at first supposed to be the same body. Later examinations have shown, however, that its immediate roof is the Henry's Fork conglomerate, and its horizon is thus established as more than two thousand feet above that of its great companion. The Steward laccolite (Figure 30) is better exposed for study. It was Fig. CO.— The Steward Laccolite. buried in the soft bad-land sandstone of the Flaming Gorge Group, and its matrix has been so far washed away that nearly the whole body of trap is HowelL |H,..,IH. I.... ,' Miles ttt^ ....m.i rnirirwiT^- N Fig. 28.— Diagram of the HiUera Cluster of Laccolitcs; Ground plau. Howe 1 1 fnlpit. Sea^Jjevp-7- E t FlG. 29. — Diagram of the Ililhrs Cluster of Laccolites; Elevation. The upper horizontal line marks the base of the Cretaceous ; the middle, the base of the Jura-Trias; the lower, the level of the sea. PULPIT ARCH, 33 revealed. It is weathered out, like a chert-nodule on the face of a block of limestone. At one end it is bared quite to the base, and the sandstone floor on which it rests is brought in sight. The waste of the sandstone has undermined its edge, and a small portion of the laccolite has fallen away. Near the opposite end a fragment of its cover of arching sandstone sur- vives— just enough to indicate that the sedimentaries were once bent over it, and that the smooth low-arching surface which now crowns it portrays the original form which the molten lava assumed. The laccolite is about two and a half miles long and one and one-half broad. The height of its eastward face, where it is sapped by the erosion of the bad-land rock, is six hundred feet, and the central depth must be more than eight hundred feet. Pulpit arch is as high and as broad as the lesser arch of Mount Holmes, but its place is not marked in the topography by an eminence for the reason that the degradation of the land lias not yet progressed so far as to unearth its core of trachyte. The drainage from Mount Hillers crosses it from west to east and has given it an oblique truncation, as illustrated in the diagram. At the upper end of the slope the Henry's Fork conglom- Fjg. 31. — Cross-section of the Pulpit arch, with ideal representation of the Pulpit Laccolite. Scale, 1 inch = 3,500 feet. 1, Vermilion Cliff Sandstone. 2, 2, Gray Cliff Sandstone. 3, 3, Flaming Gorge Shale. 4, Henry's Fork Conglomerate. 5, Tunivnk Shale. erate outcrops; at the lower end the base of the Flaming Gorge series, and in the interval the Gray Cliff sandstone is lifted to the surface. The same streams which planed away the crown of the arch have now cut themselves deeper channels and divide the massive sandstone by picturesque canons, between which it is grotesquely carved into pinnacles and ridges. A curious salient of the sandstone has given its name to the arch. How deeply the 3 n m 34 DETAILED DESCRIPTION. Pulpit laccolite lies buried is not known, no sheet nor dike of trachyte betraying its proximity. The valley of the Colorado may have to be deep- ened thousands of feet before it will be laid bare. The Jerry Butte is the most conspicuous adjunct to Mount Ilillers and topographically is more important and striking than the features which have just been described, but its structure is less clear. Its crest is formed by a great dike several hundred feet in width and two miles in length, and with an even top like those observed on Mount Holmes. The western end of the dike is the higher and forms the culminating point of the butte, and from it there radiate three other dikes of notable size. The inclosing strata, preserved from erosion only by the. shelter of the dikes, are the lower portion of the Cretaceous series, and they are so little lifted above their normal level that there is room for no considerable laccolite beneath them. The inclination of the beds is so complicated by the dips of the Pulpit, Steward, and Hillers arches, all of which are contiguous, that nothing can be made out of the form of the laccolite, if it exists. The Howell laccolite lies apart from the cluster and is well exposed. It differs from all that have been enumerated in its extreme thinness. With a breadth of more than two thousand feet, it has a depth of only fifty. Seen from the east, it might readily be mistaken for a coulee, for on that side it is the thin, hard, black cap of a table carved out of soft, sandy shale (Flaming Gorge Group) by circumdenudation. But followed westward, the table is found gradually to lose its height by the rising of the adjacent land, and at last the lava-bed runs into the slope and disappears beneath the upper layers of the same sandy shale on which it rests. How far it extends under ground can only be conjectured. How far it originally stretched in the opposite direction cannot be known because it is broken away. The original edge is concealed at one end and has been undermined and destroyed at the other, so that the only place where it can be seen is the point at which it emerges from the shale. At this point, where erosion has bared but has not yet attacked the lava, the form and character of the edge are exhibited. In place of the tapering wedge which usually terminates intrusive sheets, there is a blunt, rounded margin, and the lava scarcely diminishes in depth in approaching it. The underlying strata, locally hardened to sandstones, lie FlG. 32. — The Howell Laccolite, ;is seen from the north. FlQ. 3:5. — The Edge of the Howell Laccoljte, HOWELL LACCOLITE. 35 level ; the overlying curve downward to join them, and between the curved strata is interleaved a curved lava-sheet. In all these characters the intru- sive body is affiliated with the typical laccolites, and distinguished from the typical sheets. The laccolite which is marked "D" on the diagrams of the Hillers cluster is identical in nearly all its characters with the Howell ; it is thin and broad. One margin is wasting as its foundation is sapped ; the other is hidden from view. Its depth does not diminish toward the edge. Moreover, a few dikes issue from its margin, or from beneath its margin. It was in- truded within the same formation as the Howell (the Flaming Gorge shale), but at a horizon several hundred feet higher ; and, what is specially note- worthy, the rock of which it is composed is identical in fades with that of the Howell laccolite, and notably different from all others which were ob- served in the Hillers cluster. Thus there are grouped in this one cluster laccolites of the most varied character, differing in form, in magnitude, in the stratigraphic depth at which they were intruded, in the extent to which they have been uncovered or demolished in the progress of erosion, and also, but very slightly, in their lithologic characters. The greatest is one thousand times as bulky as the least. The length of the most obese is three times its depth ; the length of the most attenuated is more than one hundred times its depth. The one highest in the strata lies a thousand feet above the base of the Cretaceous rock series; the lowest is not higher than the summit of the Carboniferous. The latter has not yet been touched by erosion, others have been com- pletely denuded, and some have been partially demolished and removed. MOUNT PENNELL. Mount Pennell and Mount Ellen are distinct mountain masses separated by a low pass, but there is no interval between the clusters of laccolites by which they are constituted. Whether the site of a laccolite shall be marked by a mountain depends in great measure on the relation of the laccolite to the progress of erosion.. In the Henry Mountains the laccolites which have not been reached by the denudation scarcely affect the topography. The arched sedimentaries above 36 . DETAILED DESCRIPTION. them are no harder than the same strata in the surrounding plain, and they are brought substantially to the same level. It is to those which the down- ward progress of erosion has reached and passed that the mountains are due. In virtue of their hardness they survive the general degradation, and con- serve with them broad foundations of more perishable material. Mounts Ellen and Pennell mark the positions of the highest of a great cluster of laccolites, and the pass between them marks a part of the cluster where all the laccolites lie low in the strata. Mount Pennell is not so easily studied as the lower mountains at the south. Its summits are timbered and are carved into alpine forms which Fig. 35. — Cross-section of Mount Pennell. 1, Blue Gate Saudstoue. 2, 2, Blue Gate Shale. 3,3, Tununk Sandstone. The full black lines represent Trachyte. do not portray the structure but rather mask it. Upon its flanks however the topography and the structure are in so close sympathy that the latter is easily read ; and by their study some of the general features of the mount- ain have been made out. From the east and south and west the strata can be seen to rise toward it. The uprising strata on the west are the Tununk sandstone and the shales above and below it. The sandstone forms no re- vetments, but accords so closely in its dips with the slopes of the mountain that it is the surface rock over a broad area, outcropping wherever there is rock exposure. At the head of the foot-slope trachyte sheets are associated with it, some overlying and others underlying it ; and at one point a gorge reveals a laccolite not far below it — a laccolite that may or may not be the great nucleus of the mountain. On the west and south flanks the uprising strata are the Blue Gate and Tununk sandstones, with their shales. The Gate sandstone has been worn away nearly to the foot of the slope, and forms a monoclinal ridge circling about the base. The ridge is interrupted by a number of waterways, and it sends salients well up upon the flank, MOUNT PENNELL. 37 but it is too continuous to be regarded as a mere line of revetments. Tlie Tununk sandstone is not to be seen without search, being covered by heavy trachyte sheets. Trachyte sheets also underlie it, and the whole are carved into a conspicuous series of revet-crags. The association of overarching strata with sheets of trachyte leaves no doubt in my mind that the core of Mount Pennell is laccolitic, but whether it is simple or compound is not so clear. The collation of all the observed dips shows that if there be but one laccolite it has not the simplicity of form which usually characterizes them. There are low arches of the strata at the southern, northern, and north- eastern bases, which reveal no trachyte and give the impression that there may be a foundation of low-lying laccolites upon which the main trachyte mass or masses of the mountain are based. One of these low arches, that Fig. 37.— Sentinel Butte. at the northeast, is shown in the foreground of Figure 36. The strata which portray it are of the Henry's Fork conglomerate, and the laccolite which they cover is of necessity distinct from that which is revealed on the east flank of the mountain. L '» 8 DETAILED DESCRIPTION. In addition to the laccolites of the foundation and of the main body, there is a series which jut forth from the northern flank like so many dor- mer windows. They are comparatively small but are rendered conspicuous by the removal of the soft rocks which originally inclosed them. They are higher in the strata than any other observed laccolites, their position being above the Tununk sandstone and in the Blue Gate shale. The core of the main body of the mountain is probably inclosed in the Tununk shale, and the laccolites under the low arches (at the north at least) are entirely below the Cretaceous. The higher series stand on top of the low arches, and are just outside of the sheets which inclose the central body. The largest of them constitutes Sentinel Butte, and stands guard over Penellen Pass. Sapped by the yielding of its soft foundation it is rapidly wasting, and on three sides its faces are precipitous. The huge blocks which cleave from it as they are undermined strew the surrounding sir pes for a great distance. Its depth of 400 feet is made up of two layers, of which the lower is the deeper, and be- tween which there is a slight lithologic difference. The upper surface of the butte is smooth and plane with an inclination to the south. It is prob- ably a portion of the original surface of the laccolite. Thus we have in Mount Pennell a great central body consisting of a single laccolite or of a number closely massed together ; an inferior group of three or more, evidenced by low broad arches ; and a superior group of not less than four, all of which are partially destroyed. MOUNT ELLEN. The crest of Mount Ellen is as lofty as that of Mount Pennell and it is more extended. It stretches for two miles from north to south and is buttressed by many spurs. The sculpture of the crest is alpine, and the structure is consequently obscured. There are dikes of trachyte and perhaps the remnants of lacco- lites; there are Cretaceous sandstones greatly indurated; and there are Cretaceous shales baked to clinking slate; but they are all carved into smooth, pyramidal forms, and each is half hidden by the debris from the rest so that their order and meaning cannot be seen. The flanks however are full of interest to the geologist. The Ellen MOUNT ELLEN. 3D cluster of laccolites is a broad one, and all but the central portion is well exposed for study. In the spurs and foot-slopes and marginal buttes no less than sixteen individual laccolites have been discriminated, a number of them most beautifully displayed. They will be enumerated in the order of their position, beginning at the west of Penellen Pass and passing along the western, northern, and eastern flanks to the Scrope Butte, east of the pass. In the chart of the Ellen cluster, Figure 38, an attempt is made to show \ Fig. 38.— Ground Plan of the Ellen Cluster of Laccolites. the horizontal grouping of the laccolites and the order of their superposi- tion wherever they overlap. It will be observed that where the limits are imperfectly known the outlines are left incomplete, and that the central 40 DETAILED DESCRIPTION. area remains blank, not because it contains no trachyte masses, but because its alpine sculpture has prevented their study. Where it is not evident which of two encroaching laccolites is the superior, they are separated by a straight line. The line a a in the chart is the springing line of a broad, flat arch which underlies all the other arches of the western flank. If it covers but one laccolite, that one is the rival in magnitude of the Hillers nucleus, although widely different in proportions; but it is more probable that it contains a greater number. The upper surface is rolling and uneven, and has not the degree of symmetry which laccolites usually display. At the points b, c, d, and e the altitude of the arch is 3,800, 3,500, 2,000 (esti- mated) and 2,500 feet. Nevertheless there is nothing in its simple outline to indicate a compound structure ; the monoclinal ridges by which it is margined do not exhibit the flexuous curves which are commonly seen about the bases of confluent arches. Whether the nucleus is simple or compound it sends no branches to the surface ; the only outcrops of tra- chyte belong to the overlying arches. The upper parts of the arch have been so carried away that the steepness of the mountain flank is not in- • FlG. 40. — Section of the Lewis Creek Canon through the Newberry Arch. 1, Henry's Fork Conglomerate. 2, Upper portion of Flaming Gorge Shale. 3, New herry Laccolite. creased by it, and inferior strata are brought to the surface. At the north the crown of the arch bears the Henry's Fork conglomerate, while beyond its base the plateau is built of Blue Gate sandstone. At the south the arch bears the Tununk sandstone, and the Masuk lies outside H CO 4 ►1 o a- P D P^ p o o o NEWliEllIiY LACCOLITE. 41 The laccolite marled "En on the chart rests upon the Tununk sandstone. The Blue Gate shale which once buried it has been all washed away ex- cept some metamorphosed remnants upon the top, and the trachyte itself has wasted to such an extent that its original form cannot be traced. The laccolite has no near neighbor, and the erosion has left it prominent upon the mountain flank. A continuous and solitary spur joins it to the central ridge. The Newberry laccolite makes a knob 1,700 feet high, and stands by itself. Its cover of Henry's Fork conglomerate is re-enforced by a number of tra- chyte sheets, and is broken through at one point only. At that point Lewis Creek cuts with a straight course across a flank of the arch, and exposes a portion of the nucleus in section (Figures 39 and 40). The conglomerate Fig. 41.— The Geikie Laccolite (G), overlapped by the Henry's Fork Conglomerate (H H), aud the Shoul- der Laccolite (S). does not rest directly upon the trachyte, but is separated by one or two hundred feet of shale of the Flaming Gorge Group. Two miles to the northward is the Geikie laccolite, smaller than the rest 42 DETAILED DESCRIPTION. but similar in character. It lies close to the top of the Flaming Gorge shale, and is enwrapped by the Henry's Fork conglomerate. Upon three sides the conglomerate can be seen to curve over its margin from top to bottom, and upon two of these sides the curves are so broken through by erosion that the trachyte is visible within. On the north two canons cut down to the nucleus, and on the south there is a broad face of trachyte framed all about by the cut edges of the conglomerate beds. The Shoulder laccolite overlaps the Geikie, and the two are exposed in such manner as to show their relation in section. The conglomerate runs under the one and over the other and separates them. The upper laccolite is a broad and deep one, and takes its name from the fact that it makes a great shoulder or terrace on the mountain side. Toward the mountain it is buried ; toward the valley it is uncovered, and in part bounded by a cliff. It is deeply cleft by canons. It has not been subjected to measurement, but its depth is not overestimated at fifteen hundred feet nor its area at five square miles. In the sketch (Figure 42) many of these features can be traced — the Geikie laccolite at the left and the Shoulder in the center, with an outcrop of the conglomerate curving down from the roof of the one to the floor of the other, and the Newberry arch in the foreground with its cleft side. At the rear is the pyramidal Ellen Peak and the F laccolite, overlooking the Shoulder. In the distance at the left is the Marvine laccolite. Little more can be said of the F laccolite than that it exists and is the nucleus of a lofty spur. Its summit rises too nearly to the crest of the mountain to be well defined, and at its base the sedimentaries are hidden by talus. Not so the Marvine laccolite. Lying at the foot of the mountain where erosion is so conditioned as to discriminate between hard and soft, and sur- rounded by nothing firmer than the Tununk shale and Tununk sandstone, it has suffered a rapid denudation, in which nearly the whole of its cover has been carried away without seriously impairing its form. It stands forth on a pedestal, devoid of talus, naked and alone. The upper surface undulates in low waves preserving the original form as it was impressed on the molten mass. Over a portion there is a thin coating of sandstone, 3 CD a D O K o 3 cr o CO er o IT o Q CD 5? o o it V J c 6 o o - V -a s MARVINB LACCOLITE. 43 the layer next to the trachyte being saved from destruction by the indura- tion acquired during- the hot contact. From the remainder tins also has disappeared, and the contact face of the trachyte is bare. For some reason the exterior portion of the laccolite disintegrates more slowly than the inte- rior. It may be that there was some reaction from the surrounding sedi- mentables during the cooling, which modified the crystallization. Or it may be that at a later epoch a reciprocal metamorphism was induced along the contact of the diverse rocks. At all events there is a crust a few feet in thickness which is specially qualified to resist destructive agents, and which by this peculiarity can be distinguished from the trachyte of the interior. All about the northern and western faces, which are steep, this crust has been broken through and the interior excavated ; but it is only along the upper edge of the face that the crust is completely destroyed. Along the lower edge it is preserved in remnants sufficiently numerous to fully define the outline of the base. Each remnant is a sort of revet-crag standing nearly vertical and joined by a buttress to the cliff behind it. In the accompanying sketches (Figures 43 and 44) the most of these features find better expression than words can give them. The solemn order of the tombstone-like revetments is not exaggerated, nor is the contrast be- tween the ruggedness of the cliff and the smoothness of the upper crust. At the left in the upper view, and at the right in the lower, there can be seen inclined strata, the remnants of the arch which once covered the whole. The extreme depth of the laccolite is 1,200 feet, and its diameters are 6,000 and 4,000 feet. The G arch, the Dana, the Crescent, and the Maze agree in having no visible laccolites. They are mere dome-like irplifts, by which inferior beds are brought to light. Iii the middle of the Crescent arch, and there only, is a small dike. They differ in their dimensions and in their erosion and topography. The Gr arch is low and broad, and lifts the Henry's Fork conglomerate a few hundred feet only. It is covered by that bed except where Bowl Creek and one or two others cross it in shallow canons. The Dana arch bears the same relation to Mount Ellen and Jukes Butte that the Pulpit arch bears to Mount Hillers. The streams which flow down have truncated it, and afterward carved a system of canons be- 44 DETAILED DHSOlilPTION. low the plane of truncation. The Henry's Fork conglomerate overlooks it from the base of the Jukes laccolite on one side, and on the other margins it with a monoclinal ridge ; and in the interval the Flaming Gorge and Gray Cliff rocks come to the surface. ,r s r r Fig. 45. — The Jnkes Butte, as seen from the southeast, showing the Jukos Laccolite, restiug upon the Dana Arch. The Crescent arch is so perfectly truncated by the existing mountain streams that their flood-plains unite above it in a single broad slope. On the side toward the mountain there are a few insular hills of the conglom- erate, and on the side toward the plateau the same rock lifts a low mono- clinal ridge which circles about the base of the arch in a crescent. Within the crescent there are few outcrops, but it is probable that the Gray Cliff Sandstone is brought to the surface. Near the center a solitary thin dike juts forth, like a buoy set to mark the place where a laccolite is sunk. Judging the magnitude of the laccolite by the proportions of the uplift, it has a diameter of nearly four miles and a depth, of 2,500 feet; and these dimensions indicate a volume of three and a half cubic miles. The Maze arch covers a smaller area than the Crescent, but its height is greater. The drainage from the mountain crosses it on a number of CRESCENT AND MAZE. 45 lines, but there is no indication that at any recent stage of the degradation they have produced an even truncation. At present they divide the Gray and Vermilion Sandstones by so intricate a labyrinth of deep canons that the whole area of the uplift is almost impassable. The monotony of red sandstone, for here all members of the Jura-Trias are brick-red, the variety of dip, complicated to the eye by oblique lamination, the multiplicity of canons and ridges, conspire to give an impression of chaos from whatever point the tract is viewed ; and even from the most commanding stations I was unable to make out completely the arrangement of the drainage lines. Still no faults were discerned, and it is probable that the Maze arch, intri- cate as it seems, is a simple circular dome. On the north it adjoins the Crescent arch, and the monoclinal ridges of conglomerate which margin the two at the east are confluent. On the south it adjoins rather more closely one of the low arches which have been referred to the Pennell cluster. On the west, or toward the mountain, it is probably met by other arches at its own level ; but these if they exist cannot be fully known until the progressing degradation of the country shall have removed cer- tain laccolites which lie above them and slightly overlap the Maze arch. The four arches just described are of the foundation series of the east- ern base, and cover laccolites of unknown depths. Higher in the strata, and at the same time absolutely higher, is a second series, which to a cer- tain extent overlap them. The Bowl Creek encroaches on the G laccolite ; the Jukes, on the Dana and on the Bowl Creek ; the II laccolite, on the Crescent; the Peale and Scrope, on the Maze. The Boivl Creek arch is so masked by the overlapping Jukes laccolite, and by the encroachment of certain large dikes, that its general form and Fig. 46.— Cross-section of the Bowl Creek Arch, c, e marks the water-level of Bowl Creek ; 7, the Bowl Creek Laccolite ; a, a, Shales ; and s, the Gryphea Sandstone. Scale, 1 inch = 1,000 feet. proportions are not known ; but it is laid bare at one point in a fine natural section. Bowl Creek crosses it near the center, and in the walls of the canon 4G DETAILED DESCRIPTION. are exhibited two hundred feet of the laccolite, together with two hundred and fifty feet of superjacent beds. The curve of the strata is unbroken by faults or dikes, and carries them below the level of the creek at each end of the canon. Next above the trachyte lies a clay shale which has been baked to the hardness of limestone. It is one hundred feet thick, and is more or less altered throughout, as is also the sandstone which overlies it. The ex- tent of the metamorphism indicates that the trachyte mass by which it was produced is not a mere sheet, but is the body of the laccolite itself. The Juices laccolite encroaches upon the G, the Dana, and the Bowl Creek arches, and is superior to them all ; it may be said to stand upon them. The trachyte has a depth of only one thousand feet, but it lies so high with reference to the general degradation that it is a conspicuous fea- ture of the topography. The edges of the laccolite are all eaten away, and only the central portion survives. All of its faces are precipitous. The cover of shale or sandstone has completely disappeared, and the upper sur- FiG. 47. — Profile of the Jukes Butte, as seen from the northwest. face seems uneven and worn ; but a distant view (Figure 47) shows that its wasting has not progressed so far as to destroy all trace of an original even surface. The eminences of the present surface combine to give to the eye which is aligned with their plane the impression of a straight line. The hill is loftier than the laccolite, for under the one thousand feet of trachyte are five hundred feet of softer rock which constitute its pedestal, and by their yielding undermine the laccolite and perpetuate its cliffs. The H laccolite is not well exposed. It lies on one edge of the Crescent arch and is covered by the Henry's Fork conglomerate. TEALE LACCOLITE. 47 Little is known of the form of the Peale laccolite. One edge is lost in the obscurity of the alpine sculpture, and the other has been removed along with the crest of the Maze arch, on which it rested. But by this removal a section has been opened across the laccolite, revealing its internal struct- ure from top to bottom. It is shown to be composite, attaining its height of 850 feet by the compilation of three distinct beds of trachyte, separated by partings and wedges of shale. The lowest bed is thin and of small ex- tent. Next is the main bed, six hundred feet thick and a mile or more broad ; and on top is a bed two hundred feet thick and proportionately nar- row. Each of the beds is lenticular in section, and the piling of the less upon the greater produces a quasi-pyramidal form. The interleaved shale bands are metamorphosed to the condition of slate. Under the laccolite are one or two hundred feet of shale, apparently unaltered except at the con- tact. Then come the Henry's Fork conglomerate, 350 feet thick, and the Flaming Gorge shale, several times thicker. Within the upper shale is a restricted trachyte sheet and near the top of the lower shale is a broader one. The latter is double throughout, its two layers having been intruded at different times. The top of the escarpment is at the top of the laccolite, and only a short distance back from the brow are shale and sandstone resting upon the trachyte and conforming to its uneven surface. The Scrope laccolite resembles the Jukes in everything except that its erosion has progressed so far as to obliterate every trace of the original upper surface. Its position in the strata is about the same, and the erosion of its matrix has left it a conspicuous crag. It rests on the flank of the Maze arch, just as the Jukes laccolite rests on the Dana arch. The rem- nant of trachyte is less than one thousand feet high, and has been carved into a subcorneal form in which no hint of the original size and proportions of the trachyte body is conveyed. Figure 49 is a view of the east flank of Mount Ellen, as seen from Mount Hillers. It groups together many of the details that have been enumerated. The conical hill at the left is the Scrope laccolite. The spur from the mountaiu which ends just at the right of it is the Peale laccolite. The bold butte which terminates the last spur of the mountain in the dis- 48 DETAILED DESCRIPTION. tance is the Jukes laccolite. Across the base of the latter one can trace the outcrop of a hard bed. This is the Henry's Fork conglomerate, and the upward curve which it shows belongs (probably) to the Crescent arch. Nearer than the Jukes Butte and in the same direction is a low hill, mark- ing the dike within the Crescent. Just to the left of it is an insular out- crop of the conglomerate, and nearer by is another outcrop in the form of a cliff, which is continuous to the base of the Peale laccolite. Between the Peale and Scrope laccolites the conglomerate is hidden by an embayment of the cliff, and it reappears in the base of the Scrope Butte. In all these outcrops the escarpments of conglomerate face toward the east and at the same time toward the Maze and Crescent arches. On the opposite side of the arches the same conglomerate outcrops in a monoclinal ridge with its escarpment facing to the west. The ridge can be traced in the sketch from a point in the foreground under the Jukes Butte nearly to the eastern base of the butte, the course at first being almost directly toward the butte and then curving far to the right and forming the Crescent. Between the Scrope and Peale laccolites on one side and the monoclinal ridge on the other, lie the Maze and the Maze arch. Beyond the Maze arch and limited at the right by the Crescent, is the Crescent arch. The Scrope, the Peale, and the Jukes are visible laccolites ; the Maze and Crescent arches cover invisible laccolites. The determinate laccolites and arches which compose the lower slopes of Mount Ellen, while they are of prime importance for purposes of inves- tigation, must not be considered superior in number and magnitude to those of the central region. That region is known to abound in trachyte masses, and it far exceeds the marginal district in the extent and degree of its metamorphism. There is every reason to believe that the mountain crest marks the zone of greatest igneous activity, and that the foot-hills are as truly subsidiary from a geological point of view as they are from a topographic. There is no evidence of a great central laccolite, such as the Hillers and Pennell clusters possess, and I am disposed to regard the mountain as a great congeries of trachyte masses of moderate size, separated and in the main covered by shales and sandstones. The sedimentary strata of the O a ■I. S r. X -f. a u 3 -a a > 1— I ® EC a> aa O 93 0> o o o cS c3 •a TO STEREOGRAM. 49 summits are all of the Cretaceous series, but they are too greatly altered to permit the discrimination of the Masuk, Gate, and Tununk groups. The Henry's Fork conglomerate, which might have been recognized even in a metamorphic condition, was not seen. STEREOGRAM OF THE HENRY MOUNTAINS. For the double purpose of mapping and studying the mountains a model in relief was constructed, in which great pains was taken to give all the principal features their proper altitudes and proportions. This model was photographed, and has been reproduced by the heliotype process in Plate III, at the end of the volume. After it had been completed, a second model was constructed by adding to the surface of the first. Wherever the Blue Gate sandstone appeared in the original model no addition was made. Where the Tununk sandstone appeared there was added an amount equivalent to the combined thickness of the Blue Gate sandstone and the Blue Gate shale ; and in general, enough was added in every part to bring the surface up to the summit of the Blue Gate sandstone. In this way a restoration was made of the form of that sandstone previous to its erosion. It is not to be understood that the mountains ever possessed this form; for when the surface of the Blue Gate sandstone was unbroken by erosion it was unbroken only because it was covered by other strata, which while they shielded it were themselves eroded. If the sandstone had been inde- structible, this is the form which would have been developed by the wash- ing away of all the overlying beds ; and in this form are embodied the arches and domes which were impressed upon the sandstone by the up- swelling of the laccolites. The model became a stereogram of the displace- ments of the Henry Mountains, and a photograph from the stereogram appears in Plate IV. It will be observed that over the central district of Mount Ellen, where by reason of the peculiar sculpture of the rock its structure was concealed, the restoration of the sandstone was not carried ; it seemed better to repre- sent our lack of knowledge by a blank than to bridge over the interval by the aid of the imagination. If the reader will study the plate, he will find that it expresses a great 4 II M 50 DETAILED DESCRIPTION. body of the phenomena which have been described in this chapter. The simplicity of the Ellsworth and Holmes arches is contrasted with the com- plexity of the others ; the greatness of the Hillers and Pennell domes with the smallness of those which lie upon their flanks. One point that is especially striking is the relation between the upper and lower domes of the Ellen cluster. The upper, which give rise to all the conspicuous fea- tures of the mountain flanks, are comparatively small, while the lower, which might almost be overlooked in a rapid examination of the mountain, are comparatively large and constitute the great mass of the uplift. The smaller laccolites, because they are the upper, have been denuded of their covers, and in virtue of their hardness stand forth salient. The larger, be- cause they are the lower, have not been laid bare, and the comparatively feeble resistance which their covers have opposed to erosion has impressed their forms but slightly on the topography. CHAPTER IV. THE LACCOLITE. The principal facts in regard to the laccolites of the Henry Mountains having been set forth in the preceding chapter, an attempt will now be made to deduce from them the natural history of the Laccolite. There is a question which the critical geologist will be likely to pro- pound, and which should be answered at the outset. "What evidence", he may demand, "is there that the origin of the laccolite was subsequent to the formation of the inclosing strata rather than contemporaneous with it? May it not have been buried instead of intruded? May not the successive sheets and masses of trachyte have been spread or heaped by eruption upon the bottoms of Mesozoic seas, and successively covered by the accu- mulating sediments?" The answer is not difficult. 1st. No fragment of the trachyte has been discovered in the associated strata. The constitution of the several members of the Mesozoic system in the Henry Mountain region does not differ from the general constitution of the same members elsewhere. This evidence is of a negative character, but if there were no other it would be sufficient. For there is indubitable proof that at the end of the Shinarump period the Henry Mountain region was lifted above the ocean, and if any of the nuclei of the mountains had then existed they could not have escaped erosion by shore waves, and must have modified the contemporaneous deposits. 2d. The trachyte is in no case vesicular, and in no case fragmental. If it had been extruded on dry land or in shallow water, where the press- ure upon it was not sufficient to prevent the dilatation of its gases, it would have been more or less inflated, after the manner of recent lavas. If it had issued at the bottom of an ocean, the rapidity of cooling would have cracked the surface of the flow while the interior was yet molten and in motion, and 52 THE LACCOLITE. breccias of trachyte debris would have resulted. The absence of inflation and of brecciation are of course of the nature of negative evidence, but they derive weight from the fact that a great number of distinct bodies of trachyte have been examined in the course of the investigation. 3d. The inclination of the arched strata proves that they have been disturbed. If the laccolites were formed in each case before the sediments which cover them, the strata must have been deposited with substantially the dips which they now possess. This is incredible. The steepest decliv- ity of earth-slopes upon the land is 34° from the horizontal, and they have not been found to equal this under water. Prof. J. D. Whitney noted 23° as the original slope of a deposit on the Pacific Coast, and regarded it as an extreme case. The writer has made many measurements of the inclination of oblique lamination in massive sandstones, and found the maximum to be 24°. But the strata which cover the laccolites dip in many places 45° to 60°, and in the revetments of the south base of Mount Hillers they attain 80°. 4th. It occasionally happens that a sheet, which for a certain distance has continued between two strata, breaks through one of them and strikes across the bedding to some new horizon, resuming its course between other strata. Every such sheet is unquestionably subsequent to the bedding. 5th. The strata which overlie as well as those which underlie laccolites and sheets, are metamorphosed in the vicinity of the trachyte, and the greatest alteration is found in the strata which are in direct contact with it. The alteration of superior strata has the same character as the alteration of inferior. This could never be the case if the trap masses were contempora- neous with the sediments ; the strata on which they were imposed would be subjected to the heat of the lava, but the superior strata would accumulate after the heat had been dissipated. In the Henry Mountains a large number of observations were made of the phenomena at and near the contacts of sedimentary and igneous rocks, and in every instance some alteration was found. In fine, all the phenomena of the mountains are phenomena of in- trusion. There is no evidence whatever of extrusion. It is not indeed inconceivable that during the period in which the subterranean chambers UEVIEW OF TUE FACTS. 53 were opened and filled, a portion of the lava found its way to the top of the earth's crust and there built mountains of eruption ; but if such ever existed, they have been obliterated. The Henry Mountains are similar among themselves in constitution. They all exhibit dome-like uplifts; they all contain intrusive rocks; and their intrusive rocks are all of one lithologic type. They are more- over quite by themselves ; the surrounding- country is dissimilar in struct- ure, and there is no gradation nor mingling of character. Thus similar and thus isolated it is natural to regard the mountains as closely related in origin, to refer their trachytes to a common source, and to look for homology in all their parts. It was the search for such homology which led to the hypothesis that the laccolite is the dominant element of their structure. It is now time to examine this hypothesis, the truth of which has been as- sumed in the preceding pages, and see how far it accords with the facts of observation. The facts to be correlated are the following : 1st. There are seven laccolites which lie so far above the local plane of erosion that they are specially exposed to denuding agents. They have no enveloping strata, and their only associated sheets lie in the strata under them. Their original forms have beeia impaired or destroyed by erosion. They are the Scrope, the Jukes, the Sentinel and its three companions, and the A laccolites. 2d. There are two laccolites so nearly bared that their forms are unmistakable, but which are still partially covered by arching strata, and which have associated sheets and dikes. They are the Marvine and the Steward laccolites. 3d. There are five supposed laccolites situated where the erosion planes are inclined, which run under the slopes and are covered at one side or end, and at the other project so far above them as to have lost something by erosion. These are accompanied by overarching strata and by sheets and dikes. They are the Peale, the Howell, the Shoulder, the D, and the E. 4th. There are seven or eight supposed laccolites, of which only a small part is in each case visible, but which are outlined in form by domes 54 TUE LACCOLITE. of overarching strata. Their bases are not exposed. Associated with them are dikes and sheets. They are the Hillers, the Pennell, the Geikie, the Newberry, the Bowl Creek, the C, the H, and perhaps the F. 5th. There are five domes of strata accompanied by dikes and (with one exception) by sheets, but showing- no laccolite. They are the Ellsworth, the Greater Holmes, the Crescent, the Jerry, and the B arches. 6th. There are nine or more domes of strata with no visible accompani- ment of trachyte. They are the Lesser Holmes, the Pulpit, the G, the Dana, and the Maze arches, and those of the foundation of Mount Pennell and of the west base of Mount Ellen. Upon the hypothesis that all these phenomena are examples of the lac- colitic structure, they have the following- explanation: Each individual case comprised originally a laccolite, covered by a great depth of uplifted and arching strata, and accompanied by dikes and sheets which penetrated the strata to a limited distance. Lying at different depths from the surface, they have borne, and still bear different relations to the progressive degra- dation of the country, and have been developed by erosion in different de- grees. In nine of the instances cited the arch of strata has been truncated; but at so high a level that no dikes nor sheets were unearthed. In five in- stances the plane of truncation was so low that dikes and sheets were brought to light, but not the main body of trachyte. The truncation was in most of these cases less perfect because of the resistance to erosion by the hard dikes and sheets and by the strata which their heat had hardened. In eight other instances the erosion has left prominent the dome of hardened strata with its sheets and dikes, but has somewhere broken through it so as to reveal a massive core of trachyte. In five instances one side of the dome of strata has been washed away, exposing the core of trachyte to its base and showing undisturbed strata beneath it. In two instances the soft matrix has been so far washed away from the laccolite as to expose its form fully; and seven laccolites have not only lost all cover but have themselves been partially demolished. Certainly, the hypothesis accords with all the facts that have been ob- served and unites them into a consistent whole. It explains fourteen dome- like arches of sedimentary rock which are imperfectly exposed, by classing COMPOSITE STKUCTUUE. 55 them with seven other arches of the same region which have been opened in section to the base and found to contain laccolites ; and it strengthens the case by pointing to a connected series of intermediate phenomena. Until some strata-dome of the Henry Mountains, or of a closely allied mountain, shall be found to display some different internal structure, it will be safe to regard the whole phenomena of the group as laccolitic. Form of laccolites. — As a rule laccolites are compact in form. The base, which in eleven localities was seen in section, was found flat, except where it copied the curvature of some inferior arch. Wherever the ground plan could be observed it was found to be a short oval, the ratio of the two diam- eters not exceeding that of three to two. Where the profile could be ob- served it was usually found to be a simple curve, convex upward, but in a few cases and especially in that of the Marvine laccolite the upper surface undulates. The height is never more than one-third of the width, but is frequently much less, and the average ratio of all the measurements I am able to combine is one to seven. The ground plan approximates a circle, and the type form is probably a solid of revolution — such as the half of an oblate spheroid. Internal Structure. — Of the laccolites which are best exhibited in section, there are a number which appear to be built up of distinct layers. The Peale exhibits three layers with uneven partings of shale. The Sentinel shows two without visible interval. The Howell shows two. The Pennell has a banded appearance but was not closely examined. The Marvine shows at a distance a faint banding, which near by eludes the eye. No di- vision nor horizontal structure was seen in the Hillers, Jukes, Scrope, or Steward laccolites, but observation was not sufficiently thorough to satisfy me of its absence. It is probable that all the larger laccolites are composite, having been built up by the accession of a number of distinct intrusions. There is little or no prismatic structure in the trachytes. It is some- times simulated by a vertical cleavage induced in sheets and laccolites which are undergoing disintegration by sapping, but I did not observe the pecu- liar prismatic cleavage which is produced by rapid cooling in dikes, sheets, and coulees of basalt. The two structures are not often discriminated, but 56 THE LACCOLITE. they are really quite distinct, and their peculiar characters are easily recog- nized. The cleavage planes produced by cooling are as a rule perpen- dicular to the cooling surface, and the systems of prisms which are based on the opposite walls of a dike or sheet, do not correspond with each other, and do not run across, but meet midway in a confused manner. The cleav- age planes which are produced by the shearing force when a massive bed of trap or other rock is undermined or sapped and yields under its own Aveight, extend from base to top, and are perpendicular to the plane of the horizon instead of the plane of the bed.* Vertical Distribution. — The range of altitudes at which laccolites have been formed is not less than 4,500 feet, and neither the upper nor the lower limit is known. The highest that are known — those which were intruded at the highest geological horizon — are near the base of the Blue Gate shale (Middle Cre- taceous), but it is quite possible that higher ones have been obliterated by erosion. The lowest that is known was intruded in the Shinarump shale, but it is known of the invisible Ellsworth laccolite that upper Carbonif- erous strata lie above it, so that its horizon of intrusion must be still lower. The plexus of dikes and sheets on the Ellsworth arch indicates that the lac- colite is not deeply buried ; but in the series of arches there are nine which show no trachyte, and we have no data from which to infer their depth. How the laccolites are distributed within these limits is more readily comprehended by the aid of a diagram. In Figure 50 the triangles mark the horizons of determined laccolites, and the crosses the horizons which the invisible laccolites cannot exceed. For example, the base of the Scrope laccolite is visible and is seen to lie on the Tununk shale 400 feet above the Henry's Fork conglomerate; to represent it a triangle is placed at about the middle of the space representing the Tununk shale, and in the column devoted to the Ellen cluster. The upper surface of the Geikie laccolite is visible and upon it rest, first a few feet of Flaming Gorge shale, and then the Henry's Fork conglomerate; to represent it a triangle is placed near the top of the Flaming Gorge space. The crown of the Pulpit arch has *See page 172 of the "Exploration of the Colorado Eiver", by J. W. Powell. TWO ZONES. 57 been so far eroded that half of the Vermilion Cliff sandstone is shown in section, but no laccolite is revealed. It is evident that the Pulpit laccolite is lower than the middle of that sandstone; and to represent it a cross is placed below the middle of the Vermilion Cliff space and in the column devoted to the Hillers cluster. Mt. Ellen. Mt. Pennell. Mt, Hillers. Mt. Holmes. Mt. Ellsworth. { ----i — -- FEE1 -B000 -5000 -4000 -3000 -3000 -IOD0 i i y 1 Masuk Sbale ■ el = /...i 1 VI F==^== A AAAA Tuuunk Sandstone J =^^ AA A aAaA A + + A Henry's Fork Conglomerate.. loooooooo Ooo A Ji A -1- + A*£ A Gray Cliff Sandstono ■S Vermilion Cliff Sandst one lllllj 1 1 ~r i + $mm A -!- + Aubrey Sandstone ... . . ,! i i !' : Fig. 50. — Diagram of the Vertical Distribution of the Laccolites of the Henry Mountains. The first feature which this graphic assemblage yields to the eye is that there are at least two zones of laccolites. The upper ranges from the lower part of the Blue Gate Group, through the Tununk and Henry's Fork, to the upper part of the Flaming Gorge Group. The lower has not yet been fully developed by erosion, but its proximity is indicated. The Hillers lac- colite is uncovered at top, and the.dikes of the Ellsworth, the Greater Holmes, 58 THE LACCOLITB. and the Crescent have been reached. All of the invisible laccolites indi- cated in the Vermilion Cliff and Shinarump spaces must be referred to this zone; and there is reason to suspect that all but one of the invisible lacco- lites whose indication falls in the Tununk and Flaming- Gorge spaces be- long also to the lower zone. However this may be, it is not probable that the determination of the depths of the invisible laccolites would vitiate the conclusion that there is an upper zone of laccolitic frequency which is sep- arated from a lower zone by an interspace of laccolitic infrequency. Another feature illustrated by the diagram is that all the determined laccolites are inclosed by soft beds. They have been intruded into the shales, but not the sandstones. They cluster about the Henry's Fork con- glomerate, but none of them divide it. This selection of matrix is confined however to the laccolites and is not exercised by sheets and dikes. Tra- chyte sheets were seen within the Henry's Fork, the Gray Cliff, the Ver- milion Cliff, and the Aubrey sandstones. A third feature of the diagram is the restriction of the upper zone of laccolites to the northward clusters ; Mounts Ellsworth and Holmes contain laccolites of the lower zone only. This fact of distribution is correlated with a fact of denudation — namely, that in the general degradation of the country, the region about the southern mountains has lost two thousand feet more than the northern. One fact is probably the cause of the other. The absence of laccolites of the upper zone at the south may have per- mitted the greater degradation; or the greater degradation may have caused the destruction of several of the upper laccolites. The fact that the differ- ence in degradation can be independently accounted for is favorable to the latter supposition. The Colorado River which is the main artery of drain- age for the whole region, flows close to the bases of the southern mountains, and the rapid declivity from the mountain summits to the river has given and still gives exceptionally great power to the agents of erosion. No other cause is needed to explain the difference of degradation, and the absence of laccolites of the upper zone is explicable without assuming that they were never present. The negative objection to the idea that the southern mountains origi- nally possessed laccolites of the upper zone being thus disposed of, it is A LACCOLITE IN TOE AIR. 5(J worth while to inquire whether there is any evidence in its favor. If supe- rior laccolites existed, they would be sure to leave behind them a record of the conduits through which their lava was injected. A dike or a chimney must always connect a laccolite with the source of its material ; and the removal of the laccolite necessarily exposes a cross-section of its stem. The discovery of such a dike can be regarded, not indeed as a proof of the for- mer existence of a superior laccolite, but as demonstrating its possibility. The summits and flanks of Mounts Holmes and Ellsworth bear many dikes, which have been regarded as subsidiary features of the laccolites beneath them, but it is quite possible that any one of them formerly led to another laccolite above. The upper laccolite may have been first formed and then have been lifted, dike and all, when the lower was intruded ; or it may have been last formed, and been fed through a fissure which traversed the lower after its congelation. The only dike which was discovered in the vicinity of these mountains, without being upon them, stands midway between them. It is the only observed dike of the Henry Mountains (ex- cepting always the alpine district of Mount Ellen), which is not so closely associated with some laccolite as to seem an accessory feature, and its ex- ceptional position has led to the suspicion that it belonged to an overlying laccolite. Upon such uncertain evidence no positive conclusion can be based, and it is vain to build laccolites in the air. The most that can be said is that the southern mountains need not be distinguished from the northern, because at the present stage of degradation they contain laccolites of the lower zone only. The Material of the Laccolites. The intrusive rocks of the Henry Mountains were sampled with care. Specimens were selected which had undergone little decomposition and which represented all the prominent lithologic varieties. They were chosen from the trachytes of both zones and of each of the mountain masses ; and they represent dikes and sheets, as well as laccolites. From about thirty specimens thin slices were cut for microscopic examination. GO TIIE LACCOL1TE. Captain C. E. Dutton, of Omaha, Nebraska, was so kind as to under- take the study of the collection, and the letter which embodies his conclu- sions is given below. In accordance with his diagnosis I shall call the intrusive rocks porpliyriti >c trachyte; and I am glad to have the weight of his authority in support of my belief that all the rocks of the series are of one type, their resemblances far outweighing their differences. Note. — Persons desiring to examine the Henry Mountain trachytes under the microscope can obtain mounted thin sections from Mr. Alexis A. Julien, School of Mines, Columbia College, New York. REPORT ON THE LITHOLOGIC CHARACTERS OF THE HENRY MOUNTAIN INTRUSIVES. BY CAPTAIN C. E. DUTTOlSr. "I have examined with great interest and attention the Henry Mount- ain rocks you sent me, and proceed to acquaint you with such results as my limited facilities have permitted me to derive from the examination. It is a very well defined series, having some marked characters which distin- guish it from the nearest allied group with which I am acquainted. This is all the more interesting, because I am inclined to think that these pecu- liarities maj^ave a definable association with or relation to the manner in which the intrusive rocks occur in those "laccolites", as you term them. "The hand-specimens show in most cases large and unusually perfect crystals of orthoclase imbedded in a very compact uniform paste through which hornblende is also disseminated rather more abundantly than is usually the case where the dominant felspar is monoclinic. Micaceous crystals appear to be wholly wanting and this is a notable circumstance, since the trachytes of the Plateau country, to which these rocks are most nearly allied, are seldom without one or more of them. The only other min- eral which is of frequent occurrence in the specimens is magnetite (or possibly titanic iron), which is diffused in the usual form of minute granules in many of them, but is scarce in several of them. In general there is a great scarcity of mineral species and any others than those mentioned are of the greatest rarity. "The dominant felspar is orthoclase, but a portion of it is triclinic, and I presume this portion is albite, with an occasional occurrence of oligo- clase. The groundmass in which the crystals are included is in most cases (H G2 TOE LACCOLITE. decidedly compact and without distinguishable crystals, but shows between the crossed Nicols closely aggregated luminous points, which with a J-inch objective are resolved indistinctly into felspar. In some cases the crystals of the groundmass are quite apparent with an inch objective, and their species determinable. But the greater portion of the groundmass is quite amorphous, and does not polarize light at all. The proportion of crystal- line to amorphous matter in the paste is highly variable — in some cases it is quite bright between crossed Nicols, in others far less so, and in none is it entirely dark. Those specimens which have the finer and more amor- phous groundmass have the larger and more perfect crystals of felspar — an association of properties which is not wholly without qualification, but still sufficiently decided. "Turning to the included felspars, their mode of occurrence is quite an uncommon one, I believe, so far as the eruptive rocks of the Rocky Mountain region are concerned, and give rise to some hesitation before assigning them definitely to the trachytic group. In a great many cases the felspathic crystals are well developed, and so large and so nearly perfect that their aspect is decidedly porphyritic. This is especially the case with the dikes of Mounts Ellsworth and Holmes (Nos. 56, 61, 68, and 69). The orthoclase is invariably of the white "milky" variety, with the exception of a single specimen from a Mount Ellsworth dike (No. 57), where it is present as sanidin. (This is an exceptional rock in all respects, and will be spoken of hereafter.) Nearly all of them appear to have been subject to altera- tion by chemical action since their formation as is indicated by their diminished power to polarize light. Whether this is due to atmospheric weathering or to changes en masse it is of course impossible to distinguish with certainty, though I incline to the latter view since it is manifested as decidedly in specimens which show no external indications of weathering as in those which do show them. It is not uncommon to find crystals which have almost entirely ceased to polarize. The zonal arrangement is very common in the crystals, and some of the zones contain numberless minute fluid cavities in the largest crystals. The foreign substances included in the crystals present no novelty, being the ordinary films of hornblende, CAPTAIN DUTTON'S REPORT. 63 minute needles of felspar, granules of magnetite, and those dust-like points of brownish yellow color which are the proper inclusives of the groundmass. "The orthoclase occasionally presents the adular variety, but this never becomes a marked feature. I have observed the same in many of the trachytes of the High Plateaus and of the Great Basin. Another phenomenon is the occurrence of crystals which are quite typically mono- clinic at one end (orthoclase), and at the other end have the arrangement of plagioclase. This is well known elsewhere, and described by Zirkel. (Mik. Beschaff der Mineralien u. Gesteine). "In classifying these rocks therefore, we may observe that they pre- sent a blending of the characteristics which are common to trachyte and felsitic porphyry. Those who regard porphyry as a distinct class of erup- tive rocks would have no hesitation in calling Nos. 18, 56, 61, 68, and 69 undebatable felsitic porphyries, and to the same series might with propriety be added No. 33. With equal confidence Nos. 16, 20, 35, and 43 may be called unqualified trachytes. The other rocks are intermediate in character between these two extremes, and the whole may be regarded as a series in which the individuals form a graduated scale. "You will recall the fact that many lithologists object to the terms por- phyry or porphyritic being used to designate a distinct class or group of rocks, holding that they merely characterize a single feature which is more or less frequently presented by all igneous rocks and having no necessary relation to any of them, and that this is no more adequate to such an impor- tant distinction than the color or relative degree of fineness or coarseness of texture. Although this la.tter view seems to me to underrate the distinctive value of the porphyritic character in general, I incline very decidedly to the belief that it is true as applied to these Henry Mountain rocks. Here at least the porphyritic character has but little significance. In some varieties the crystals are larger and more perfect and the groundmass more homo- geneous; in others the crystals are smaller and imperfect, and the ground- mass more coarse and irregular; while still others are 'betwixt and between'. The most careful scrutiny fails to show any fundamental differences in the groundmass or in the included minerals. Hence I think these rocks would 04 THE LACCOLITE. be accurately designated as a group by calling them porphyritic trachytes. Such varieties as Nos. 16, 20, and 35 may by themselves be called simply trachyte, the porphyritic character being insufficiently distinct in them to warrant any qualification of the name. "There is one specimen (No. 57, from dike in Shinarump shale, Mount Ellsworth) which constitutes an exception to the foregoing. By inspection of a hand-specimen it might hastily pass for a very compact andesite, but the observer will be instantly undeceived hj applying the miscroscope. It consists of imperfect crystals, which must be sanidin, imbedded in a very close groundmass composed of a material which differs from the foregoing tra- chytes in being wholly amorphous. Between crossed Nicols the paste trans- mits no light whatever, though between the parallel Nicols it closely resem- bles the others. The hand specimen is very dark colored (gray), but the slide is sufficiently translucent. The felspar crystals are either fragmental or very imperfectly developed as to their edges and angles, but polarize very sharply. The amount of twinning is very small, but it appears occasionally. The rock is undoubtedly a trachyte, but an unusual one. Lta|dark color is not due to hornblende nor to magnetite, both of which occur in it very sparingly, especially the»former. "I have already remarked that the only frequent minerals besides fel- spar are hornblende and magnetite. Apatite occurs and is tolerably plen- tiful in a few of the specimens, but absent from most of them. The crystals are all small, requiring a low power for the determination of the larger and a high power for the smaller. They present no peculiarities. Of very rare occurrence is nepheline. This mineral is usually associated with the more basic volcanic rocks and seldom penetrates the trachytic group. Quartz is almost equally rare. The absence of any great variety in the mineral spe- cies is quite normal, except possibly the total absence of mica, which is usually present and frequently the only associate of felspar in the western trachytes. The Henry Mountain rocks do not so far as I can discover contain a trace of it. "In answer to your particular inquiries — "1st. 'Is the paste vesicular, or is there any evidence in the crystals to indicate the pressure under which they were formed1?' I can only say that CAPTAIN DUTTON'S REPORT. G5 the paste is extremely compact and contains no vesicles even in those speci- mens of which the aspect is most decidedly trachytic. Some of the larger crystals of felspar contain an abundance of pores or vesicles which may have contained liquids, but with a J-inch objective they are too small for treatment by the method you refer to. A few large cavities, usually of irregular shape, occur, but I am quite unfamiliar with the practical treat- ment of this subject and cannot advise you. I do not find any cavities still containing fluids, and I presume that even if they existed they would be difficult if not impossible to gauge on account of the impellucidity of the felspar. I presume quartz is the most favorable mineral for this investiga- tion on account of its transparency and the greater frequency of its large cavities. Quartz however is almost the scarcest of the contents of these rocks. "2d. 'Do any mineralogic differences correlate with the superficial or geographic distribution of the rocks?' and "3d. 'Do any mineralogic differences correlate with the vertical dis- tribution of the trachytes % ' As it appears from your account of the dis- tribution of the i'1 sses that the upp zone belongs (with one exception) to Mounts Ellen and Penneii and the lower to tlie other mountains, the answer to one is the answer to both, and this is in the negative. The mineralogical differencea^are exceedingly small, considering the number of distinct masses, and this covers the inquiry entirely. Regarding the text- ure or habitus, on the contrary, it appears to me that the true trachytes predominate in the upper zone and the porphyries in the lower, but not without exceptions. "4th. 'Do any mineralogic differences correlate with the size of the intrusive masses'?' No mineralogical differences thus correlate, but I find a preponderance of the porphyritic texture in the smaller masses and of the trachytic texture in the larger. It is not without exception, and the pre- ponderance is small." Metamorphism and Contact Phenomena. — Wherever the trachytes came in contact with the sedimentaries the latter were more or less altered. Large bodies of trachyte produced greater changes than small. The laccolites both metamorphosed their walls more completely, and carried their influence 5 H M 66 THE LACCOLITE. to a greater distance than the sheets and dikes. The summits of the lacco- lites had a greater influence than the edges ; a phenomenon to which I shall have occasion to revert. The sandstones were less affected than the shales, at least in such characters as readily catch the eye. Clay shales were indurated so as to clink under the hammer, and Captain Dutton dis- covered with the microscope that minute crystals of felspar had been de- veloped. Sandstones were usually modified in color, and their iron was segregated so as to give a mottled or speckled appearance to the fracture. They were indurated, but the granular texture was always retained. The trachyte carries numerous small fragments of sedimentary rock broken apparently from its walls, and these are as thoroughly crystalline as their matrix. The altered rocks are usually jointed, but nothing approaching to slaty cleavage was seen, nor has there been any crumbling. The reciprocal influence of the sandstone and shai 'ttpon the trachyte was small. Specimens brokenwfrom th$ c intact »*:'face :>!*& laccolite and from its interior cannot b"e disting^^^a^ \n he Marv aefljaccolite how- ever there is a difference between tW$-'-extt, "1:11 jntey * portions in their ability to withstand erosion, * * # Historical. — Before leaving th|e subject ,a Jn^ 4r^jpture of the mount- ains it is proper to place on record Krtairj -obSewations by others which antedated my own but have never been published! While Professor Powell's boat party wM exploring the cations of the Colorado, Mr. John F. Steward a geologist and member of the party climbed the cliff near the mouth of the Dirty Devil River and approached the eastern base of the mountains. He reported that the strata had in the mountains a quaquaversal dip, rising upon the flanks from all sides. The following year Prof. A. H. Thompson then as now in charge of the geographic work of Professor Powell's survey crossed the mountains by the Penellen Pass and ascended some of the principal peaks. He noted the uprising of the strata about the bases and the presence of igneous rocks. In 1873 Mr. E. E. Howell at that time the geologist of a division of the Wheeler Survey traveled within twelve miles of the western base of the mountains, and observed the uprising of the strata.. NEWBERRY ON THE SIERRA ABA JO. (J 7 My own observations were begun, in 1875, at which time a week was spent among the mountains. They proved so attractive a field for investi- gation that in the following year a period of nearly two months was devoted to their study. Other Igneous Mountains. — The Henry Mountains are not the only igneous group which the Plateau province comprises. They are scattered here and there throughout its whole extent. From the summits of the Henry Mountains one can see the Sierra La Sal ninety miles to the northeastward, and the Sierra Abajo seventy miles to the eastward. Beyond them and two hundred miles away are the Elk Mountains of Colorado. Fifty miles to the southwestward stands the Navajo Mountain on the brink of the Colorado; and one hundred and twenty miles to the southeast the Sierra La Lata and the Sierra Carriso are outlined against the horizon. Westward it is less than thirty miles to the.Aquarius Plateau, the nearest member of the great sys- tem of volcanic tables among which the Sevier and Dirty Devil Rivers rise. Beyond the horizon at the solith and southwest and southeast are a series of extinct volcanoes; MountWTaylor and the Marcou Buttes in New Mexico; the Sierra Blanca, the o II: a Mogollon, the San Francisco Group and the Uinkarets in Arizona; ai^the Panguitch Lake Buttes in Utah. Of the groups which are visible, all but that of the Aquarius Plateau are allied in character to the Henry Mountains. The Sierra Abajo was studied in 1859 by Dr. J. S. Newberry, geolo- gist of the Macomb Expedition, who writes: "Within the last few weeks we have been on three sides of this sierra, and have learned its structure quite definitely. It is a mountain group of no great elevation, its highest point rising some 2,000 feet above the Sage-plain, or perhaps 9,000 feet above the sea. It is composed of several distinct ranges, of which the most westerly one is quite detached from the others. All these ranges, of which there are apparently four, have a trend of about 25° east of north, but be- ing arranged somewhat en echelon, the most westerly range reaching farthest north, the principal axis of the group has a northwest and southeast direc- tion. The sierra is composed geologically of an erupted nucleus, mainly a gray or bluish-white trachyte, sometimes becoming a porphyry, surrounded 68 THE LACCOLITE. by the upheaved, partially eroded, sedimentary rocks. The Lower Creta- ceous sandstones and Middle Cretaceous shales are cut and exposed in all the ravines leading- down from it, while nearly the entire thickness of the Cretaceous series is shown in spurs which, in some localities, project from its sides; apparently the remnants of a plateau corresponding- to, and once connected with, the Mesa Verde. Whether the Paleozoic rocks are any- where exposed upon the flanks of the Sierra Abajo I cannot certainly say, though we discovered no traces of them. It is, however, probable that they will be found in some of the deeper ravines, where, as in most of these iso- lated mountains composed mainly of erupted material, they are doubtless but little disturbed, but are buried beneath the ejected matter which has been thrown up through them. "The relations of the Cretaceous rocks to the igneous nucleus of the Sierra Abajo are very peculiar, for, although we did not make the entire circuit of the mountain mass, and I can, therefore, not speak definitely in regard to the western side, as far as our observations extended we found the sedimentary strata rising on to the trachyte core, as though it had been pushed up through them." (Geology of the Macomb Expedition, page 100.) Of another group Dr. Newberry says in the same report (page 93) : "Of the composition of the Sierra La Sal we know nothing except what was taught by the drifted materials brought down in the canons through which the drainage from it flows. Of this transported material we saw but little, but that consisted mainly of trachytes and porphyry, indicating that it is composed of erupted rocks similar to those which form the Sierra Abajo, of which it is in fact almost an exact counterpart. From the cliffs over Ojo Verde we could see the strata composing both the upper and second plateaus, rising from the east, south, and southwest on to the base of the Sierra La Sal, each conspicuous stratum being distinctly traceable in the walls of the canons and valleys which head in the sierra. It is evident, therefore, that the rocks composing the Colorado Plateau are there locally upheaved, precisely as around the Sierra Abajo * * *." These mountain groups have been since visited by the geologists of Dr. Hayden's survey, Dr. A. C. Peale ascending the Sierra La Sal and Mr. W. H. Holmes the Sierra Abajo. Mr. Holmes has also examined the La Lata. NAVAJO MOUNTAIN. 69 and Carriso Mountains and found in them the same upbending of Creta- ceous strata and the same association of igneous material. The Navajo Mountain has been viewed by Mr. Howell and by the writer from a commanding position on the opposite side of the Colorado River, and fragments of its trachyte have been gathered on the river bank by Professor Powell, but no geologist has yet climbed it. Still there can be no question of its general structure. It is a simple dome of Jura- Triassic sandstone, springing abruptly from a plateau of the same material, and veined at the surface by sheets and dikes of trachyte — the counterpart in fine of Mount Ellsworth, only of more imposing proportions. The La Sal, the Abajo, the La Lata, the Carriso, the Navajo, and the Henry Mountains agree in their essential features. Structural^ they have no trends. Their phenomena are grouped about centers and not axes. In all of them the strata are lifted into dome-like arches, and associated with these arches are bodies of trachyte. The trachytes are all of one lithologic type, and are so closely related that a collection of rock speci- mens representing all the groups would show scarcely more variety than a collection representing the Henry Mountain laccolites. With so many characters in common they can hardly fail to agree in the possession of laccolitic nuclei.* The Elk Mountains are at the very margin of the plateau, and geo- graphically might be connected with the Sawatch Range which bounds * While these pages are passing through the press a paper by Dr. A. C. Peale "On a peculiar type of eruptive mountains iu Colorado" (Bulletin U. S. Geol. Sur., Vol. Ill, No. 3) comes to hand. He groups together as of one type not only the Elk, La Sal, Abajo, La Lata, and Carriso Mountains, but also the Spanish Peaks, Park View Mountain, Mount Guyot, Silverheels Mountain, the San Miguel Mountains, the La Plata Mountains, and certain smaller masses in Middle Park and near the Huerfano Eiver. He says, "Although modified in several instances, the general plan appears to be the same. The igneous material came up through fissures in the sedimentaries, sometimes tipping up their ends, and sometimes passing through without disturbing them. On reaching the Cretaceous shales, it generally spread out in them, and pushed into and across them dikes and intrusive sheets of the same igneous rock. The eleva- tion in some cases appears to be due to actual upheaval caused by the eruptive force. The mountains as they now exist are doubtless largely the result of erosion, the hard igneous rock opposing greater resistance to erosive influences than do the surrounding soft sedimentary beds." 70 THE LACOOLITE. the plateau province on that side. But structurally they are a group in- stead of a range, and affiliate with the groups which are insulated by an environment of tables. Thanks to the labors of Mr. Holmes and Dr. Peale their general structure is known. The Eastern Elk Mountains consist of four great bodies of " eruptive granite ", over which are arched not only Mesozoic but Paleozoic strata. Their foundation must be a floor of Archaean metamorphics. Two of them, the Snow Mass and White Rock laccolites, are joined by a continuous line of disturbance, in the description of which by pen and pencil Mr. Holmes has made an important contribu- tion, not only to dynamical geology, but to the methods of geological illustration. The others are more symmetric and are complementary illustrations of the common structure. One, the Sopris, is half truncated by erosion so that the core is exposed at top with an encircling fringe of upturned sedimentaries ; and the other, the Treasury, retains a complete arch of Paleozoic strata. The Western Elk Mountains are a cluster of smaller laccolites which are inserted between strata of Cretaceous age. Their traps include porphyritic trachytes undistinguishable from those of the Henry Mountains, and eruptive granites identical with those of the Eastern Elk Mountains; and they exhibit a gradation from one to the other. Indeed the two rocks are nearly related, and their assignment to classes so diverse as trachyte and granite is merely an illustration of the imperfection of our classification of rocks. The description of the Elk Mountains will be found on pages 61 to 71 and 163 to 168 of the Annual Report for 1874 of the " Geological and Geographical Survey of the Territories." If we turn now to the distinctivelv volcanic mountains of the Plateau province — to those which are built by eruption at the surface — we leave at once the porphyritic trachytes. Mount San Francisco, Mount Bill Will- iams, Mount Sitgreaves, Mount Kendrick, Mount Floyd and the Sierra Blanca (of Arizona) are all composed of basic trachytes, and so are the Aquarius Plateau and the many tables that lie beyond it. The Mogollon group, the Marcou Buttes, the minor cones about Mount San Francisco, the Uinkarets, and the Panguitch Lake group are ba- saltic. In each of these instances the igneous rock issued above the sur- CORRELATION OF ROOKS AND STRUCTURES. 71 face and there is no evidence by displacement that any portion of it was deposited below. Mount Taylor may be an exception. In the character of its lava and its general features it resembles Mount San Francisco, but there are dis- turbed strata on its southern flank, and it is possible the mountain is both extrusive and intrusive. Extrusion and intrusion are probably combined in some small tables lying fifty miles north of the Henry Mountains. They are built of Flaming Gorge shale, preserved from erosion by dikes, sheets, and (probably) outflows of basalt. Combining all these facts we attain to a simple relation between two types of igneous rock on the one hand, and two types of mountain struct- ure on the other. One type of rock is acidic, including "porphyritic tra-* chyte" and "eruptive granite", and its occurrence is without exception intrusive. The other type of rock is basic, including basic trachyte and basalt, and its occurrence is almost uniformly extrusive. It is not possible to combine the two groups of phenomena by saying that in one case the eruptive cones cover laccolites, and in the other the laccolites have been covered by eruptive cones which have disappeared ; first, because many of the eruptive cones are too well exposed to admit of the concealment of laccolitic arches beneath them ; second, because the two types of lava are essentially different. The acidic type if extruded at the surface would be an ordinary trachyte ; the basic type if crystallized under pressure would be classed with the greenstones. The basis for the generalization is exceedingly broad. I have enu- merated only seven groups of laccolitic mountains and ten groups of erup- tive ; but with few exceptions each group is composed of many individu- als, each one of which is entitled to rank as a separate phenomenon. In the Uinkaret Mountains Professor Powell has distinguished no less than one hundred and eighteen eruptive cones, and in the Henry Mountains I have enumerated thirty-six individual laccolites. In one locality basic lava has one hundred and eighteen times risen to the surface by channels more or less distinct, instead of opening chambers for itself below. In the other locality porphyritic trachyte has thirty-six times built laccolites instead of rising to the surface. 72 THE LACCOLITE. If our attention was restricted to these two localities we might as naturally correlate the types of structure with some accidents of locality as with types of lava ; but when all the localities are taken into account it is evident that there is no common mark by which either the laccolitic or the volcanic are distinguished. THE QUESTION OF CAUSE. We are now ready to consider the question: Why is it that in some cases igneous rocks form volcanoes and in other cases laccolites? It is not necessary to broach the more difficult problem of the source of volcanic energy. We may assume that molten rock is being forced upward through the upper portion of the earth's crust, and disregarding its source and its propelling force may restrict our inquiry to the circumstances which determine its stopping place. Let us further assume, but for a moment only, that the cohesion of the solid rocks of the crust does not impede the upward progress of the fluid rock, nor prevent it from spreading laterally at any level. The lava will then obey strictly the general law of hydrostatics, and assume the station which will give the lowest possible position to the center of gravity of the strata and lava combined. (1) If the fluid rock is less dense than the solid, it will pass through it to the surface and build a subaerial mountain. (2) If the upper portion of the solid rock is less dense than the fluid, while the lower portion is more dense, the fluid will not rise to the surface but will pass between the heavy and light solids and lift or float the latter. (3) If the crust be composed of many horizontal beds of diverse and alternating density, the fluid will select for its resting place a level so conditioned that no superior group of successive beds, including the bed immediately above it, shall have a greater mean specific gravity than its (the fluid's) own; and that no inferior group of successive beds, including the bed immediately beneath, shall have a less mean specific gravity than its own. HYDROSTATIC EQUILIBRIUM. 73 [In the diagram, a series of light and heavy beds are represented in section by open and shaded spaces. A lava stream free to move upward or laterally will intrude it- self at some point (c) so placed that every com- bination of superior beds (a), which includes the lowest, shall have a less average density; and every combination of inferior strata (5), which in- c\ eludes the highest, shall have a greater average density than that of the lava. J The first case is that of a volcano ; the second is that of a laccolite ; and the third is the general case, including the others and applying to all volcanoes and laccolites. Conversely we may say that, given a series fig. 51.— Diagram to illustrate the r , , c V 1 ~\x. j.' i *i. application of the law of Hydro- oi strata ot diverse and alternating- density, a **. v .,., . . +, * „ o J ' static Equilibrium to the move- very light lava will traverse it to the top and be n,ents of lavas- Tbe sbad«d ^ . n . .,, . , hands represeut heavy strata; extruded ; a heavier will intrude itself at some the open, light. lower level ; and a series of dissimilar lavas may select an equal number of distinct levels. It is easy to imagine such a balancing of conditions that a slight change in a lava will determine a great change in its level of intrusion. Having seen the general application of the hydrostatic law, it is time to recall the condition which we laid aside at the start. Cohesion, or rigidity, is never absent and must affect every phase of vulcanism. It certainly op- poses the free circulation of lavas, and it cannot but modify their obedience to the hydrostatic law. But granting this, and believing that a full comprehension of the sub- ject must include this condition, I am at a loss to tell in what way it influ- ences the selection by a lava flood of a subaerial or a subterranean bourne. Whether it will on the whole oppose upward progress more than lateral, or .vice versa, is not clear. If it resists lateral intrusion the more strongly, it favors the formation of volcanoes; if it resists upward penetration the more strongly, it favors the formation of laccolites; and in either case the working of the hydrostatic law is modified. 74 TOE LACCOLITE. But in neither case is the working- of the law more than modified. The law is not abrogated, and in obedience to it light lavas still tend to rise higher than heavy however much the rising of all lavas may be hindered or favored. In brief, since lavas are fluids they are subject to the law of fluid equilibrium, and their behavior is conditioned by the relations of their densities to the densities of the solids which they penetrate; and since the latter solids are rigid and coherent, it is further conditioned by the resist- ance which is opposed to their penetration. When the resistance to pene- tration is the same in all directions, the relation of densities determines the stopping place of the rising lava; but when the vertical and lateral resistances are unequal, their relation may be the determining condition. If we can decide whether the determinative condition in the Plateau region was that of densities or that of penetrability, we shall have solved our problem. Assuming, first, that the essential condition is that of penetrability, we should expect that some particular stratum or that a few particular strata, being less penetrable than others, would check the rising lavas and accu- mulate them in a system of laccolites, which would occupy one, or a few definite horizons. Volcanoes would occur in districts from which such impenetrable strata either were originally absent or had been removed before the igneous epoch; and we should expect to find the same variety of material in laccolites and in volcanoes. Assuming, second, that the essential condition is that of densities, we should expect as before to find certain stratigraphic horizons more favora- ble than others to the accumulation of laccolites, and we should also expect to find certain lavas usually volcanic and certain others usually laccolitic. That is to say — since the condition of impenetrability resides in the solid rock only, and the condition of density pertains to both solid and fluid, either condition might determine laccolites at certain stratigraphic horizons, while the latter only could discriminate certain lavas as intrusive and others as extrusive. The vertical distribution of laccolites is not inconsistent with either as- sumption. In the Henry Mountains there are two zones of occurrence; in DENSITY Oil PENETRABILITY ? 75 the Eastern Elk Mountains there is a third; and it is probable in the pres- ent state of our knowledge that all other laccolites of the Plateaus can be assigned to one or another of these. The fact that the laccolites of the upper zone have a vertical range of two thousand feet is rather favorable to the idea that their stations were determined by relations of density, but is not decisive. When however we turn to the relation between the constitutions and the behaviors of lavas, we find the entire weight of the evidence in favor of the assumption that conditions of density determine the structure. The co- incidence of the laccolitic structure with a certain type of igneous rock is so persistent that we cannot doubt that the rock contained in itself a condi- tion which determined its behavior. We are then led to conclude that the conditions which determined the results of igneous activity were the relative densities of the intruding lavas and of the invaded strata; and that the fulfillment of the general law of hydrostatics was not materially modified by the rigidity and cohesion of the strata. Having reached this conclusion it is natural to seek for confirmation by the investigation of the densities of the rocks concerned in the phenom- ena. As will appear by a table given further on, the density of the Henry Mountain trachyte has been determined to be 2.61 ; but the densities of the erupted lavas of the Plateaus are not yet known. There can be no doubt however that the latter are heavier. Von Cotta in his Lithology gives 2.9 to 3.1 as the density of basalt, .and 2.6 to 2.9 as the density of the more basic trachytes. And in general, it is well established that where the state of aggregation is the same, basic igneous rocks are always heavier than acidic. But in order that the laccolitic structure should have been deter- mined by density, the acidic rock of the laccolites must have been heavier in its molten condition than the more basic rocks of the neighboring volca- noes; and since in the crystalline condition the acidic is the lighter, it follows that it has gained less density in cooling than the basic. If the amount of contraction of the several rocks in passing from their natural molten condition to the crystalline condition could be determined experimentally, a crucial test would be applied to our conclusions as to the 76 THE LACCOLITE. origin of laccolites. The matter is however beset with difficulties. Biscliof attempted by melting eruptive rocks in clay crucibles to obtain their ratios of expansion and contraction, but his method involved so many sources of error that his results have been generally distrusted. He concluded that the contraction in passing from the molten to the crystalline state is greater in acidic than in basic rocks. Delesse by an extended series of experiments in which crystalline rocks were melted and afterward cooled to glasses, showed that acidic rocks increase in volume from 9 to 11 per cent, in pass- ing from the crystalline state to the vitreous, while basic increase only 6 to 9 per cent. Mallet concluded from some experiments of his own that the contraction of rocks in cooling from the molten condition is never more than 6 per cent, and that it is greater with basic than with acidic rocks; but considering that the substances which he treated were artificial and not nat- ural products, that his methods were not uniform, and that he ignored the distinction between the vitreous and the crystalline, of which Delesse had demonstrated the importance, no weight can be given to his results. If however all of these experiments were trustworthy and their results were concordant, their bearing upon the problem of the laccolites would still be slight. It is generally conceded that the fusion of lavas is hydro- thermal, while in all the experiments recourse was had to dry fusion ; and the densities attained in the two ways are necessarily different. The prac- tical difficulty in the way of restoring the natural molten condition is great and may be insuperable, but unless it shall be overcome we cannot learn experimentally the changes of density which igneous rocks undergo in congelation. There is a fact of observation which tends to sustain the view that the laccolitic rocks contracted less in cooling than the volcanic. The prismatic structure is produced by the contraction of cooling rocks during and after solidification. That it does not occur in the Henry Mountain trachytes indi- cates that their contraction was small. That it does occur at numerous local- ities in Utah in basalts, indicates that their contraction was relatively great. Mr. Jukes, in his Manual of Geology, says that it is most frequently exhibited in "doleritic lavas and traps, being especially characteristic of basalt, but occurs almost as perfectly in some greenstones and felstones"; DENSITIES OF TRACHYTES. 77 and in the range of my own observation I can recall no instance of its occur- rence in other than basic rocks. For the sake of comparing- the densities of the intrusive rocks with those of the strata which contain them, a number of determinations were made of the specific gravities of specimens representative of the trachytes and of the several sedimentary groups of the Henry Mountains. Trachytes were selected to represent as great a variety of locality and relation as possible, and at the same time exclude all specimens which showed traces of decomposition. Hand specimens weighing from one hundred to four hundred grains were used, and these were weighed first dry, and then suspended in water. By using such large quantities averages were obtained of a rock which, minutely considered, is heterogeneous; and by using the blocks entire instead of pulverized or granulated, the state of aggregation of its minerals was included as an element of the specific gravity of the rock. It will be observed that the range, 2.54 to 2.66, is very small. Table of Specific Gravities of Trachytes of the Henry Mountains. Locality. East flank of Mount PenneR; sheet Marviue Laccolite; north base of Mouut Ellen Peale Laccolite; east flauk of Mount Ellen Dike ou Mount Ellsworth South base of Mount Hillers ; sheet Sheet under the Peale Laccolite Scrope Laccolite ; southeast base of Mount Ellen Bowl Creek Laccolite; northeast base of Mount Ellen North spur of Mount Peunell ; dike Sentinel Laccolite; north base of Mount Pennell Mean Specific gravity. 2.6G 2.65 2.64 2.64 2.63 2.62 2.60 2.58 2.58 2.54 2.61 Specimens to represent the stratigraphic series were selected at the margins of the disturbed region so far as possible, to avoid the effect of metamorphism. But as it was not practicable to eliminate this source of error in every case, the densities of highly metamorphic specimens were 78 TI3E LACCOLITE. also measured for the purpose of indicating the effect of the metamorphism. In order to restore so far as practicable the condition of the rocks at the time of the lavic intrusion, the specimens were saturated with water, and in this condition were weighed in air as well as in water. The results for the porous sandstones are from one-seventh to one-fourteenth lower than would have been obtained by the usual method. Hand specimens were used as before. Table of Specific Gravities of Sedimentary Boclcs of the Henry Mountains. Kock. Condition. Specific gravity. 1 2 3 4 5 C 7 8 9 10 11 Masuk Sandstone Blue Gate Sandstone / Blue Gate Shale Flaming Gorge Shalo Gray Cliff Sandstone Vermilion Cliff Sandstone, (top) Vermilion Cliff" Sandstone, (base) Henry's Fork Conglomerate Vermilion Cliff Sandstone Aubrey Sandstone Tunnnk Shale Unaltered Unaltered Unaltered Unaltered Unaltered Unaltered (?) . . Unaltered (?) .. Slightly altered Altered Altered Altered 2.1(5 2.14 2.45 2.42 2.13 2.21 2.28 2.25 2.48 2. 55 2.(i9 It is plain from this table that the effect of the metamorphism was to increase the densities of the rocks affected. The Blue Gate shale which unaltered gave 2.45, is lithologically identical with the Tununk shale which altered gave 2.69. The Aubrey sandstone cannot be observed unaltered in the vicinity of the mountains, but at a distance of forty miles where it again comes to the surface it closely resembles the Gray Cliff sandstone. If it has the same normal weight as the latter, then it has increased from 2.13 to 2.55. The specimens of the Vermilion Cliff sandstone numbered 6 and 7 were not visibly changed, but as they were obtained from the flank of the Holmes arch there was reason to suspect that their condition was not normal,, and the determined densities strengthen the suspicion. Judged by other locali- DENSITIES OF SEDIMENTARIES. 79 ties, the normal density of the Vermilion Cliff rock is not far from that of the Gray Cliff rock, namely 2.13; and it is easy to believe that the' upper portion of the bed where it lay on the side of the Holmes arch was changed in density to 2.21 ; while the lower portion lying- nearer the laccolite was changed to 2.28; and while the same bed among the Ellsworth dikes ac- quired the density of 2.48. Taking into account both these considerations and certain others which need not be enumerated, I derive the following : Table of the Specific Gravities of the Henry Mountain Sedimentary series in the Order of Superposition. Bed. • Specific gravity. 2.16 estimated . . 2.40 Blue Gate Sandstone 2.14 Blue Gate Shale 2.45 2. 15 Tununk Shale estimated.. 2. 45 Henry's Fork Conglomerate 2.25 Flaming Gorge Shale 2.42 Gray Cliff Sandstone - - -. 2.13 Vermilion Cliff Sandstone .. estimated. . 2.15 Shinarump Shale estimated. . 2.40 2. 15 Taking into account the thicknesses of the several beds enumerated in the foregoing table, it is easy to obtain the mean specific gravity of all which lie above a given horizon; and by making this determination for the horizon of the base of each of the indicated beds, the following table has been derived. The figures are based on the assumption that the rock series included nothing above the Masuk sandstone. If (as is probable) there were Tertiary beds also, the estimates are too low, for the Tertiaries of the vicinity are calcareous and argillaceous and consequently dense. 80 THE LACCOLITE. Table showing the Mean Specific. Gravities of the Rock Series contained between certain horizons and the summit of the Masuk Sandstone. Horizons. Base of Masuk Sandstone Base of Masuk Shale Base of Blue Gate Sandstone Base of Blue Gate Shale Base of Tununk Sandstone Base of Tununk Shale Base of Henry's Fork Conglomerate. Base of Flaming Gorge Shale Base of Gray Cliff Sandstone Base of Vermilion Cliff Sandstone. .. Base of Shinarump Shale Specific gravities. 2. IG 2.28 2.23 2.32 2.31 2.34 2.33 2.36 2.33 2.32 2.33 From this it appears that the laccolites of the upper zone, extending from the lower part of the Blue Gate Shale to the upper part of the Flam- ing Gorge Shale, bore loads of which the mean densities were from 2.31 to 2.34, and that laccolites of the lower zone, which has its upper limit in the Shinarump Shale, bore loads of which the mean densities were 2.32 and upward. If the positions of the laccolites were determined purely by the law of hydrostatic equilibrium, then these figures define the density of the molten trachyte, and show that its contraction in cooling — from the density 2.34 to the density 2.61 — was about one-tenth of its volume. THE STRETCHING OF STRATA. It has been the opinion, not only of the writer but of other students of the displacements of the West, that the ordinary sedimentary rocks, sandstone, limestone, and shale, are frequently elongated as well as com- pressed by orographic movements, and that this takes place without any appreciable metamorphism ; but it is difficult to find opportunity for the demonstration of the phenomenon by measurement. When a fold is made in a level stratum, either of two things may take place ; the portions of the stratum which remain level at the sides may approach each other ; or the stratum may be stretched. But when a circular portion of a continuous STRETCHED STRATA. 81 level stratum is lifted into a quaquaversal arch (as illustrated in Figure 11), an approach of the level portions is out of the question, and there must be a stretching" or a fracture. Of the unfractured quaquaversals of the Henry Mountains there is one which combines all the essentials of a crucial case. The Lesser Holmes arch is nearly isolated ; on three sides it rises from the undisturbed plateau, and on the fourth it joins a similar but fractured dome. Tig. 52. — Cross-section of an uplifted dome. The dot ted lines show the original position of a bed ; the curved lines, the imposed. The major part of its surface is composed of one bed, the Vermilion Cliff sandstone, broken only by erosion. Comparing the length of this bed in its present curved form with the space it must have occupied before it was upbent, I find that in a distance of three miles it has been elongated three hundred feet. Moreover there is every reason to suppose that the elonga- tion was produced quickly, or at least by a succession of finite rather than infinitesimal increments ; for the lifting of the arch was caused by the in- trusion of a laccolite, and though the latter may have been built by the addition of many separate lava flows, it could not have risen with secular and continuous slowness. The molten trachyte, rising through a passage and into a reservoir that were comparatively cool, would have clogged itself by congelation had it not moved with a certain degree of rapidity. The condition which rendered possible the elongation and the sudden bending of so rigid and brittle a rock as a massive sandstone, was pressure. At the time of the uplift the sandstone was buried by other sediments to a depth of from five thousand to eight thousand feet, and sustained a pressure of from five thousand to eight thousand pounds to the square inch. Now the experiments which have been made upon building stones show that the weight required to crush similar sandstones in a dry condition, is three thousand to five thousand pounds to the inch ; and it is a fact familiar to quarrymen that sandstone and limestone which are quarried below the water level are both softer and weaker while they are still satu- rated than they are after drying. So we may fairly assume that the Ver- 0 II M 82 THE LACCOLITH*. milion sandstone was loaded at the time of its displacement with a crushing weight. No part could yield to the pressure while it was sustained by the surrounding parts ; but every part was ready to yield whenever its support was withdrawn. It was in a quasi-plastic state and abhorred a fissure as strongly as ''nature abhors a vacuum", and for the same reason. A fissure could not be opened in it unless it was coincidently filled by something — such as lava — which would resist the tendency of its walls to flow together. The formation of a gaping fissure being thus prevented, and the uplifting of the dome requiring that the sandstone should cover a greater area, an extension of the bed was the necessary result. It was not stretched into the dome form ; it was compressed. The efficient force did not act in the direc- tion of the extension, but vertically. The sandstone was pushed, not pulled. If this explanation is the true one, then it is true in general that just as for each rock there is a crushing weight, so there is for each rock a cer- tain depth at which it cannot be fissured and can be flexed. The softer rocks are plastic at small depths. Fire-clays under coal-seams exude, or "creep", even with the pressure of a few feet of superincumbent strata. Springs of water rise at the outcroppings of soft strata because the joints which intersect most rocks near the surface of the ground cannot cross those which are soft enough to yield under the pressure incident to them. If the soft beds were jointed they would not intercept percolating water, and the distribution of springs would be very different. The phenomena of fissure veins are in point. When a fault takes place, and one rock mass is slidden past another to which it had been joined it is usually the case that the opposed surfaces no longer fit together as they did before the movement, and interspaces are left. These become filled, at first by water, and afterward by minerals deposited from the water, and the mineral masses thus deposited are called fissure veins. But the preservation of the interspaces depends upon the rigidity of the rocks which inclose them; and it frequently happens that where a system of rocks is traversed by a fault, the harder will keep somewhat apart and maintain a fissure, while the softer will be crushed together without an interspace. If the mineral vein which forms in such a fissure is afterward DOWNWARD LIMIT TO FISSURE VEINS. 80 explored in mining-, it is found to be traceable and continuous so far as it is walled by the hard rock upon both sides, but when the hard is replaced by the soft in one or both walls, the vein is either reduced to a mere fillet or disappears completely. If the fault extends to a great depth, it will finally reach a region where the hardest rocks which it separates are co- erced by so great a pressure that they cannot hold themselves asunder, but are forced together before the fissure can be filled by mineral deposits. Thus there is a definable inferior limit to the region of vein formation ; and even while it is impossible to assign a downward limit to the fault which made place for a vein, it may be possible to assign a downward limit to the vein itself. Accordant with this view is the absence' of fissure veins from the Henry Mountains. Displacement and thermal disturbance are usually regarded as the conditions of mineral concentration ; and here were displacement and lavic intrusion coincident in time and place. The heat which meta- morphosed great bodies of shale and sandstone was surely competent to excite the currents and reactions which concentrate minerals in veins ; but the displacements did not open fissures, and the heated water could circu- late only through the pores of rocks. Fissure veins were impossible, and the sluggish currents which were engendered in continuous rock masses did not effect a great change in the distribution of minerals. THE CONDITIONS OF ROCK FLEXURE. There are three known conditions under which strata of the most rigid character may be bent without fracture; or in other words there are three ways in which flexibility may be either induced or demonstrated. At ordinary temperatures and at the surface of the earth a hard stratum cannot be quickly flexed. But no rigidity is absolute, and a constant strain, even though slight, will in the course of time produce deformation. The same result may be accomplished quickly if the temperature of the stratum is raised to near the point of fusion. Or it may be accomplished with neither great heat nor great time if only the stratum is so deeply buried that the weight of its cover keeps it from opening fissures. The three conditions of flexure are time, heat, and pressure ; and whenever the circumstances of a 84 THE LACCOLITE. displacement include none of these, the rocks are broken. A fourth condi- tion, moisture, is of great importance as an accessory, but alone it is not sufficient to prevent fracture. The whole body of strata of the earth's crust is saturated with water, except a very little at the surface, and all rock movements are thereby facilitated. If the strata were dry, the*ir flexure would require much more time, or heat, or pressure, than is necessary in their moist condition. Often the three conditions complement each other ; but not always. We may say, the greater the load which strata bear the more rapidly they can be flexed ; and conversely, the more slowly strata are displaced the less the pressure necessary to prevent fracture. And we may say, the higher the temperature of strata the more rapidly they can be flexed ; and conversely, the more slowly strata are displaced the lower the temperature necessary to prevent fracture. For both these statements we find support in a great series of homolo- gies. But we cannot affirm that such a reciprocal relation exists between the effects of heat and pressure. For all rocks are believed to expand by heating, up to the point of fusion; and it is a recognized physical law that in all bodies which heat expands, the effects of heat are opposed by press- ure. Hence we cannot say, "The heavier the load which strata bear the lower the temperature necessary to prevent fracture", nor can we say, "The higher the temperature of strata the less the load necessary to prevent fracture". THE QUESTION OF COVER AND THE QUESTION OF AGE. It is evident that the laccolites of the Henry Mountains were formed beneath the surface of the earth's crust, but at what depth is not so evident. The problem is involved with the problem of the age of the laccolites, and the two are connected with the general history of the Basin of the Colorado. Neither problem can be called, for the present at least, determinate, but it is possible to narrow them down by the indication of limits which their solu- tions will not exceed. So much of the Colorado Plateau region as lies within Colorado and Utah was covered during a geological age which it is convenient to call EARLY HISTORY OF THE COLORADO RIVER. 85 Cretaceous, by a sea, the waters of which appear to have become fresh toward the last. Then came elevation both general and differential. A great part of the sea bed became dry land, and the accumulated sediments together with many which underlay them were bent into great waves thou- sands of feet in altitude. The crests of the waves were subjected to erosion and truncated. Then came a second submergence which was purely lacus- trine. In some way that has not been ascertained a lake basin was formed, and the region received a new system of sediments which it is convenient to call Tertiary, and which not merely filled the troughs between the great rock-waves but covered the truncated summits of the waves themselves. Then followed the desiccation of the basin by the cutting down of its rim where the water overflowed. The overflowing river as it deepened its channel and gradually lowered the lake, steadily extended its upper course to follow the receding shore; and finally when the basin was completely drained the river remained, its channel leading through what had been the deepest part of the Tertiary sea. That river is the Colorado. As portions of the lake bottom were successively drained they began at once to be eroded, and from that time to this there has been progressive degradation. The regions nearest to the central river were reduced most rapidly and have been completely stripped of their Tertiary strata, but broad areas of the latter remain at the west, and north, and east. (The reader will understand that this succinct history is shorn for the sake of clearness of all details and qualifications. There have been com- plicating eruptions and displacements or oscillations at every stage, and if the full story could be told, it would not be by a single paragraph nor by a single chapter.) When the Cretaceous strata were thrown,, into waves the site of the Henry Mountains remained in a trough, and it probably was not dried, but continued the scene of sedimentation while the crests of the surrounding rock-waves were worn away. Certainly it was not greatly eroded at that time; and when the Tertiary lake beds were thrown down it was favorably disposed for a heavy deposit. It is not extravagant to assume that four thousand feet of lake beds rested on the Masuk sandstone at the beginning of the final desiccation. 86 THE LACCOLITE In brief tliere may be distinguished — 1. The deposition of the Cretaceous. 2. The folding- and erosion of the Cretaceous. 3. The deposition of the Tertiary. 4. The desiccation of the Tertiary lake basin. 5. The erosion Avliich is still in progress. It is evident that the laccolites were not formed until the Cretaceous strata had been deposited; for their uplifts have bent and tilted all Creta- ceous rocks up to and including the Masuk sandstone. They were not formed at any late stage of the final erosion, for they con- serve tables along their western base, which but for their shelter would long since have disappeared. From the end of the Cretaceous period to the end of the desiccation of the basin there is no event with which the laccolites can be directly connected. There is however a consideration which in an indirect way sanctions the opinion that the epoch of igneous activity was after the deposition of the Tertiaries and before their erosion. The Masuk Sandstone is at once the summit of the Cretaceous and the highest bed in the present Henry Mountain section. If it were restored over the entire range, the laccolites of the upper zone would have on the average thirty-five hundred feet of cover, and those of the lower zone nearly seven thousand feet. This was the depth of their original cover, if they were intruded at the close of the Cretaceous age. During the epoch of Tertiary deposition and the subsequent epoch of erosion, the cover first increased in depth and then diminished, having its maximum at the end of the Tertiary deposition. If it can be shown that the original cover of the upper laccolites exceeded thirty-five hundred feet, the question of age will be reduced to comparatively narrow limits. In order to discuss the problem of the original depth of cover it will be necessary to consider another mat- ter, of which the connection will not at first be apparent. The size of laccolites. — It is a matter worthy of note that no laccolite of inconsiderable extent is known in the Henry Mountains. The smallest which has been measured is more than half a mile in diameter, and the NO SMALL LACCOLITES. 87 largest about four miles. The phenomenon does not occur upon a small scale, but has a definite inferior limit to its magnitude. Let us seek an explanation of this limit. The dome of strata which covers a laccolite has for its profile on every side a monoclinal curve. In Figure 52 the section of a dome exhibits a monoclinal flexure in s a and again in s b; and the dome being approxi- mately circular this flexure completely surrounds it. We may even de- scribe or define the dome as a monoclinal flexure encircling a point or a space. Considering now that when the laccolite was injected the over- lying strata were lifted, and that this disturbance was communicated up- ward to the then existing surface of the earth, we may properly speak of the lifted body of rock as a cylinder bounded on every side by a mono- clinal flexure. Furthermore, since the monoclinal flexure is the structural equivalent of the fault*, we may render our conception still simpler by replacing in imagination the encircling flexure by an encircling fault, and picturing to ourselves the uplifted rock mass as a simple cylinder, perfectly divided from the surrounding rock and slidden upward so as to project above the surface an amount equal to the depth of the laccolite. It is possible to give a mathematical expression to the force necessary to produce such a circular fault. Disregarding lithologic differences, the resistance to the rupture is measured by the area of the faulted surface, or what is the same thing, the area of the convex surface of the cylinder. Representing the resistance to be overcome by r, the height of the cylinder (equal to the depth of the cover of the laccolite) by d, and its circumference by c, we have r = dcO (1), in which C is a function of the cohesion of the material and is constant. The force by which the cylinder is lifted and by which it is assumed that the faulting is accomplished, is communicated through the molten lava of the forming laccolite. Being thus communicated it is applied equally to all parts of the base of the cylinder, and its efficient total is measured * Exploration of the Colorado, pp. 182-184. Explorations West of the 100th Meridian, Vol. Ill, p. 48. American Journal of Science, July, 1876, p. 21. 88 TUE LAOCOLITE. by the area of that base. A part of it is devoted to lifting the weight of the cylinder, and the remainder is devoted to the making of the fault. Each of these parts is proportioned, like the whole, to the area of the base of the cylinder, or to the area of the laccolite. Representing the portion applied to the faulting by /, and the area of the laccolite by «, we have f=aCf in which C, is a constant, and a function of the pressure under which the lava is injected. c2 Substituting for a its equivalent, j — and substituting Gn for the constant term G. 4:7t /= ? 0„ (2) Equation 1 gives an expression for the resistance which cohesion can oppose to the uplift of the cylinder. Equation 2 gives an expression for the force exerted by the fluid laccolite toward overcoming the resistance of co- hesion. It is evident that for a given value of d it is possible to assign a value of G so large that / will be greater than r, or so small that / will be less than r. That is to say, at a given depth beneath the surface a lacco- lite of a certain circumference will be able to force upward the superjacent cylinder of rock, while a laccolite of a certain smaller circumference will be unable to lift its cover. Or in other words, there is a limit in size beneath which a laccolite cannot be formed. When a lava forced upward through the strata reaches the level at which under the law of hydrostatic equilibrium it must stop, we may con- ceive that it expands along some plane of bedding in a thin sheet, until its horizontal extent becomes so great that it overcomes the resistance offered by the rigidity of its cover, and it begins to uplift it. The direction of least resistance is now upward, and the reservoir of lava increases in depth instead LIM1TAL AKEA. 89 of width. The area of a laccolite thus tends to remain at its minimum limit, and may be regarded as more or less perfectly an index of that limit. In equations 1 and 2, if / == r, then c2 C„ = d c G C or c = dyr (3) // That is to say, if the force exerted by the lava is barely sufficient to overcome the resistance to uplift, then the circumference of the laccolite is proportional to the depth of its cover. Or in other words, the (linear) size of a laccolite is proportioned to its depth beneath the surface. If now we return from the faulted cylinder which for simplicity's sake has been hypothecated, to the actual cylinder which is surrounded by a flexure instead of a fault, can we retain our conclusions'? With certain mod- ifications I think we can. The strains developed in deformation by flexure are less easy of analysis than those which arise in faulting, but the two cases are in some degree analogous. The expression (equation 2) for the force which the lava applies to de- formation is unaffected by the manner in which the strata yield. The expression (equation 1) for the resistance to deformation by fault- ing involves two terms, each in its simplest relations; the resistance varies directly as the circumference of the laccolite, and it varies directly as the depth of the cover. In order to pass to an expression for the resistance to deformation by flexure, only one of these terms need be changed. The re- sistance bears the same relation to the circumference of the laccolite; but it is no longer simply proportional to the depth of the cover. It varies more rapidly. If the covering strata were all of a given thickness, were identical in kind, and were free to slide upon each other without friction, their total re- sistance to deformation would be equal to the resistance of a single stratum multiplied by the number of strata. But since they are not free to slide one upon another, they sustain each other, and the resistance offered by the combination is greater than that product. 90 THE LACCOLITE. I am led by the analogy of allied problems in mechanics to assume that the resistance of the body of strata varies with some power of its depth, but I am unable to say what power. So far as I am aware, neither mathe- matical analysis nor experimentation has been directed to the problem in question. According- to Rankine "the resistances of flexure of similar cross- sections [of elastic beams] are as their breadths and as the squares of their depths" ("Applied Mechanics", page 316), and it is possible that the same law applies to the resistances which continuous strata oppose to the uplifts of domes. But it appears more probable that the greater complexity of the strains developed in the formation of domes causes the depth to enter into the formula with a higher power than the second. On the other hand, some allowance should be made for the fact that the elasticity of the resisting strata is imperfect. If we call the power with which the depth enters the formula a, equa- tion 1 becomes r — dac Cin (4). and equation 3 becomes c - da^LL (5). It is probable that the true value of a is not less than 2, nor more than 3. Interpreting these equations in the same manner as those applying to deformation by faulting, we reach the following conclusions: 1st. At a given depth beneath the surface, lava injected under a given pressure cannot form a laccolite of less than a certain area. This may be called its limited area. 2d. The pressure of injection remaining constant, the limital area of a laccolite is a direct function of its depth beneath the surface. The limital area is greater when the depth is greater, and less when the depth is less. 3d. A laccolite of small volume will not exceed the limital area, but will grow by lifting its cover. If however the volume of intruded lava be great, its own weight becomes a factor in the equilibrium of forces and mod- ifies the distribution of the pressures. As the rock bubble rises, the weight of the contained fluid is progressively subtracted from the pressure against its top, and this proceeds until the upward and lateral pressures become LIMITAL THICKNESS. 91 proportional to the resistances which severally oppose them. Further ex- pansion is then both upward and outward. 4th. There is a limit to upward expansion, dependent on the fact that the pressure due to the combined weight of the laccolite and cover cannot exceed the pressure of the intrusive lava. Regarding the intrusive pressure as constant, it is divisible into three parts, of which one sustains the weight of the cover, also constant; another sustains the weight of the fluid lacco- lite, and is measured by its thickness or depth ; and the third produces de- formation. When the sum of the weights of the cover and laccolite equals the total pressure of the intrusive lava, uplift ceases, and the maximum depth or thickness is attained. We may call this the limited thickness. With re- gard to simple laccolites the limit is absolute, but it applies only to the dis- tinct layers of those which are composite; for a composite laccolite, built by successive intrusions at wide intervals of time, may be relieved of part of its load by the erosion of the mound which its expansion causes at the surface of the land. A laccolite formed beneath the bottom of a sea has a greater limital thickness than one formed beneath a land surface; for the superjacent water being displaced and thrust aside, is to that extent subtracted from the load to be lifted. 5th. The laccolite in its formation is constantly solving a problem of " least force", and its form is the result. Below, above, and on all sides its expansion is resisted, and where the resistance is greatest its contour is least convex. The floor of its chamber is unyielding, and the bottom of the laccolite is flat. The roof and walls alike yield reluctantly to the pressure, but the weight of the lava diminishes its pressure on the roof. Hence the top of the laccolite becomes broadly convex, and its edges acutely. Local accidents excepted, the walls oppose an equal resistance on every side; and the base of the laccolite is rendered circular. The second of the conclusions enunciated above is susceptible of test by observation. By selecting those laccolites of which the dimensions are known with the best degree of approximation, the following table has been formed: (J2 THE LACCOL1TE. \ -^ ™. , Diameters • Formations. Titles of Laccohtes. ., Means. in miles. Blue Gate Shale Sentinel 7 .7 Geikie 8 A 9 (Marvine 1.0 i Jukes 1.4 \ Upper Zone.. / ^Peale 1.8 1 z1-2 Steward 1.0 Flaming- Gorge Shale . { __ " "_ ^14 Newberry 1.8 C :... 1.9 Dana 2.0 Greater Holmes . . 2. 1 Lesser Holmes 2. 1 /Ellsworth ' 2.3' Lower Zone / \ o a Pulpit .... 2.3' Maze 2.8' Crescent 3. 6 Hillers 3.9 There is no laccolite of the upper zone so large as the smallest in the lower zone; and the mean diameter of those in the lower zone is double the mean of those in the upper. The measurements do not give the diameters of limital areas, but it is presumable that the actual areas bear substantially the same relation to the limital in the two zones. If we select the smallest laccolites in each group as those most likely to express the limital areas, the result is practically the same. RELATION OF DIAMETERS TO DEPTHS. 93 Formations. Diameters. Means. Tununk Shale . - ) .9 \ .9 Upper Zone <( ' y 1.0 Flaming Gorge Shale ) '^ ( 1.05 1.1 s 2.0 Lower Zone <^ 2.1 V 2.1 2.1 The mean for the lower zone is still double the mean for the upper. The confirmation of the conclusion is as nearly perfect as could have been anticipated. There is no room to doubt that a relation exists between the diameters of laccolites and the depths of their intrusion. Having determined by observation the mean size of the laccolites in the upper and lower zones, as well as the interval which separates the two zones, and knowing approximately the law which binds the size of the lac- colite to its depth of intrusion, we can compute the depth of intrusion of each zone. Our result will doubtless have a large probable error, but it will not be entirely without value. Let x represent the thickness in feet of the original cover of the lacco- lites of the upper zone; and x + 3300 the thickness of the cover of the laccolites of the lower zone. The mean circumference in feet of the upper laccolites is 1.2 n X 5280 = 6336 n. The mean circumference of the lower laccolites is 2.6 tt X 5280 = 13728 n. Substituting these values in equa- tion 5, we obtain and 6336 n - xa -£" 13728 it - (x + 3300) a ^-' 94 THE LACCOLTTE. Dividing the second equation by the first and reducing, 3300 x — 13728__1 (6). ?/ 6336 To obtain a minimum result, assume a — 2 ; then 3300 a? = 13728 zz 7000 feet, \J 6336 and x + 3300 = 1 0300 feet. The summit of the Masuk sandstone is 3,500 feet above the mean level of the upper laccolites ; subtracting this from the value of x gives 3,500 feet as the depth of Tertiary strata which overlay the Masuk beds during the epoch of laccolitic intrusion. To obtain a maximum result, assume a zz 3 ; then 3300 zz 11200 feet, 13728 1 $/ 6336 x + 3300 zz 14500 feet, and the result for the depth of the Tertiary strata is 7,700 feet. I am far from attaching great weight to this speculation in regard to the original depths of the laccolite covers. It is always hazardous to attempt the quantitative discussion of geological problems, for the reason that the conditions are apt to be ' both complex and imperfectly known ; and in this case an uncertainty attaches to the law of relation, as well as to the quanti- ties to which it is applied. Nevertheless after making every allowance there remains a presumption that the cover of the laccolites included some thousands of feet of Tertiary sediments. What evidence we have then, indicates that the epoch of laccolitic in- trusion was after the accumulation of deep Tertiary deposits and before the subsequent degradation had made great progress — that it was at or near the close of the epoch of local Tertiary sedimentation. DESCRIPTION OF FRONTISPIECE. 95 If the reader would realize the relation between the eroded material and the surviving- mountains, let him turn to the Frontispiece. A perspect- ive view is there given of a tract ten miles square, with Mount Ellsworth in the center. It is represented as cut Out from all surroundings by vertical planes which descend to the level of the ocean. The southern or nearer half of the block shows the present aspect of the country; the remote half shows the form it is supposed to have had if the uplift was completed before the erosion began, or what is the same thing, the form it would have, had there been no erosion. The difference between the two represents the total amount of the material that has been washed away since the completion of the Tertiary sediments. Partly in review, let us now sketch the HISTORY OF THE LACCOLITE. When lavas forced upward from lower-lying reservoirs reach the zone in which there is the least hydrostatic resistance to their accumulation, they cease to rise. If this zone is at the top of the earth's crust they build volcanoes ; if it is beneath, they build laccolites. Light lavas are more apt to produce volcanoes ; heavy, laccolites. The porphyritic trachytes of the Plateau Province produced laccolites. The station of the laccolite being decided, the first step in its forma- tion is the intrusion along a parting of strata, of a thin sheet of lava, which spreads until it has an area adequate, on the principle of the hydrostatic press, to the deformation of the covering strata. The spreading sheet always extends itself in the direction of least resistance, and if the resist- ances are equal on all sides, takes a circular form. So soon as the lava can uparch the strata it does so, and the sheet becomes a laccolite. With the continued addition of lava the laccolite grows in height and width, until finalty the supply of material or the propelling force so far diminishes that the lava clogs by congelation in its conduit and the inflow stops. An irruption is then complete, and the progress of the laccolite is comparable with that of a volcano at the end of its first eruption. During the irrup- tion and after its completion, there is an interchange of temperatures. The 96 THE LACCOLITE. laccolite cools and solidifies ; its walls are heated and metamorphosed. At the edges, where the surface of the laccolite is most convex, the heat is most rapidly dissipated, and its effect in metamorphism is least. A second irruption may take place either before or after the first is solidified. It may intrude above or it may intrude beneath it ; and observation has not yet distinguished the one case from the other. In any case it carries forward the deformation of cover that was begun by the first, and combines with it in such way that the compound form is symmetric, and is substantially the same that would have been produced if the two irruptions were com- bined in one. Thus the laccolite grows by successive accretions until at length its cooled mass, heavier and stronger than the surrounding rocks, proves a sufficient obstacle to intrusion. The next irruption then avoids it, opens a new conduit, and builds a new laccolite at its side. By successive shiftings of the conduit a group of laccolites is formed, just as by the shift- ing of vents eruptive cones are grouped. Each laccolite is a subterranean volcano. Fig. 53, Diagram to illustrate the relation of Dikes and Sheets to the Strains which are developed in the uplifting of laccolitic arches. The strata above the laccolite are bent instead of broken, because their material is subjected to so great a pressure by superincumbent strata that it cannot hold an open fissure and is quasi-plastic. But although quasi- plastic it is none the less solid, and can be cracked open if the gap is in- stantaneously filled, the cracking and the filling being one event. This happens in the immediate walls of the laccolite, and they are injected by dikes and sheets of the lava. The directions of the cracks are normal to the directions of the extensive strains (strains tending to extend) where they occur. From the top of the laccolite dikes run upward into the roof, SOLIDITY A LOW GRADE OF PLASTICITY. 97 marking- horizontal strains {a a). From the sides smaller vertical dikes run outward, marking horizontal, tangential strains. And parallel to the sides near the base of the laccolite, are numerous sheets, marking strains directed outward and upward (c c). These last especially serve to show that the rigidity of the strata is not abolished, although it is overpowered, by the pressure which warps them. Here we are brought face to face with a great fact of dynamic geology which though well known is too often ignored. The solid crust of the earth, and the solid earth if it be solid, are as plastic in great masses as wax is in small. Solidity is not absolute but relative. It is only a low grade of plasticity. The rigidity or strength of a body is measured by the square of its linear dimensions, while its weight is measured by the cube. Hence with increase in magnitude, the weight increases mere rapidly than the strength ; and no very large body is strong enough to withstand the press- ure of its own weight. However solid it may be, it must succumb and be flattened. When we speak of rock masses which are measured by feet, we may regard them as solid ; but when we consider masses which are meas- ured by miles, we should regard them as plastic. The same principle is illustrated by the limital area of laccolites. A small laccolite cannot lift its small cover, but a large laccolite can lift its correspondingly large cover The strength or rigidity which resists de- formation is overcome by magnitude. Laccolites of Other Regions. — In many lands geologists have observed intrusive rocks occurring in great bodies, but I am not aware that such a system as that of the Henry Mountains has ever been described. Doubtless all such bodies are laccolitic, but the combination of conditions which this field presents can rarely be repeated. In the first place the strata which here contain the laccolites lay level. They had suffered no displacement before the epoch of irruption, and they have suffered none since. The lac- colitic phenomena stand by themselves, with nothing to mar their sym- metry or complicate their study. In the next place the laccolites are here assembled in such number and with such variety of size, form, and hori- zon that there is little danger of mistaking accidental features for essential. Again, the region having been recently elevated is the scene of rapid 7 H M 98 TTTE LACCOLITE. degradation. Waterways are deeply corraded, slopes are steep, and escarp- ments abound. And finally the climate is so arid that vegetation is exceed- ingly scant. The rocks are for the most part bare and their examination is unobstructed. If the conditions of erosion and climate had been unfavorable in the Henry Mountains, they could not have yielded the key to the laccolitic structure ; but the key once found, it is to be anticipated that the structure will be recognized in other laccolites of which the exposures are less per- fect. If the strata had experienced anterior displacements so as to be in- clined, folded, and faulted, a symmetrical growth of laccolites would have been impossible, and the mountains would not have yielded a knowledge of the type form. But the type form being known, it is to be anticipated that in disturbed regions aberrant forms will be recognized and referred to the type. Possible Analogues of the Laccolite. — All the arches of the Henry Mount- ains have been ascribed to laccolites, whether their nuclei were visible or concealed, and the evidence upon which the latter were included appears to admit of no controversy. The question arises whether the great flexures of the Plateau region may not be allied in structure. The volcano having its homologue in the laccolite, may not broad lava fields have their homo- logues beneath displacements of the Kaibab type ? The idea is naturally attractive to one who has made a special study of laccolites, but it is hardly tenable. There are indeed many points of re- semblance between such flexures as the Waterpocket, and the uplifts of the Henry Mountains; but the points of contrast are equally conspicuous, and seem to mark a radical difference. There is a certain symmetry of form which is characteristic of the laccolitic arches, but which is rarely seen in the great flexures. And there is a linear element which is characteristic of the latter, but not of the for- mer. The great flexures always have direction or trend, and often exhibit parallelism ; the laccolitic arches betray no trend either individually or collectively. These features are well shown in Plate II, where the Waterpocket flexure is contrasted with the Henry Mountain arches. CHAPTER V. LAND SCULPTURE. The Basin of the Colorado offers peculiar facilities for the study of the origin of topographic forms, and its marvelous sculpture has excited the interest of every observer. It has already made notable contributions to the principles of earth sculpture*, and its resources are far from exhausted. The study of the Henry Mountains has not proved entirely unfruitful, and for the sake of showing the bearing of its peculiar features upon the gen- eral subject, I shall take the liberty to restate certain principles of erosion which have been derived or enforced by the study of the Colorado Pla- teaus. I.-EROSION. The sculpture and degradation of the land are performed partly by shore- waves, partly by glaciers, partly by wind; but chiefly by rain and running water. The last mentioned agencies only will be here discussed. The erosion which they accomplish will be considered (A) as consisting of parts, and (B) as modified by conditions. A. PROCESSES OF EROSION. All indurated rocks and most earths are bound together by a force of cohesion which must be overcome before they can be divided and re- * Geology of the " Colorado Exploring Expedition ", by J. S. Newberry, p. 45. " Exploration of the Colorado Eiver of the West ", by J. W. Powell, p. 152. " Geology of the Uinta Mountains ", by J. W. Powell, p. 181. " Explorations West of the 100th Meridian ", Vol. Ill, Part I, by G. K. Gilbert, pp. G7 and 554. " The Colorado Plateau Region" in American Journal of Science for August, 1876, by G. K. Gilbert. A portion of the last paper is repeated, after modification, in the first section of this chapter. 99 100 LAND SCULPTURE. moved. The natural processes by which the division and removal are accomplished make up erosion. They are called disintegration and trans- portation. Transportation is chiefly performed by running water. Disintegration is naturally divided into two parts. So much of it as is accomplished by running water is called corrasion, and that which is not, is called weathering. Stated in their natural order, the three general divisions of the process of erosion are (1) weathering, (2) transportation, and (3) corrasion. The rocks of the general surface of the land are disintegrated by iveathering. The material thus loosened is transported by streams to the ocean or other receptacle. In transit it helps to corrade from the channels of the streams other material, which joins with it to be transported to the same goal. Weathering. In weathering the chief agents of disintegration are solution, change of temperature, the beating of rain, gravity, and vegetation. The great solvent of rocks is water, but it receives aid from some other substances of which it becomes the vehicle. These substances are chiefly products of the formation and decomposition of vegetable tissues. Some rocks are disintegrated by their complete solution, but the great majority are divided into grains by the solution of a portion ; and fragmental rocks usually lose by solution the cement merely, and are thus reduced to their original incoherent condition. The most rigid rocks are cracked by sudden changes of temperature ; and the crevices thus begun are opened by the freezing of the water within them. The coherence of the more porous rocks is impaired and often de- stroyed by the same expansive force of freezing water. The beating of the rain overcomes the feeble coherence of earths, and assists solution and frost by detaching the particles which they have par- tially loosened. When the base of a cliff is eroded so as to remove or diminish the support of the upper part, the rock thus deprived of support is broken off PROCESSES OF EROSION. 101 in blocks by gravity. The process of which this is a part is called cliff- erosion or sapping. Plants often pry apart rocks by the growth of their roots, but their chief aid to erosion is by increasing the solvent power of percolating water. In general soft rocks weather more rapidly than hard. Transportation. A portion of the water of rains flows over the surface and is quickly gathered into streams. A second portion is absorbed by the earth or rock on which it falls, and after a slow underground circulation reissues in springs. Both transport the products of weathering, the latter carrying dissolved minerals and the former chiefly undissolved. Transportation is also performed by the direct action of gravity. In sapping, the blocks which are detached by gravity are by the same agency carried to the base of the cliff. Corrosion. In corrasion the agents of disintegration are solution and mechanical wear. Wherever the two are combined, the superior efficiency of the lat- ter is evident ; and in all fields of rapid corrasion the part played by solu- tion is so small that it may be disregarded. The mechanical wear of streams is performed by the aid of hard mineral fragments which are carried along by the current. The effective force is that of the current ; the tools are mud, sand, and bowlders. The most important of them is sand ; it is chiefly by the impact and friction of grains of sand that the rocky beds of streams are disintegrated. Streams of clear water corrade their beds by solution. Muddy streams act partly by solution, but chiefly by attrition. Streams transport the combined products of corrasion and weathering. A part of the debris is carried in solution, and a part mechanically. The finest of the undissolved detritus is held in suspension ; the coarsest is rolled along the bottom ; and there is a gradation between the two modes. There is a constant comminution of all the material as it moves, and the 102 LAND SCULPTURE. work of transportation is thereby accelerated. Bowlders and pebbles, while they wear the stream-bed by pounding and rubbing", are worn still more rapidly themselves. Sand grains are worn and broken by the con- tinued jostling, and their fragments join the suspended mud. Finally the detritus is all more or less dissolved by the water, the finest the most rapidly. In brief, weathering is performed by solution ; by change of tempera- ture, including frost ; by rain beating ; by gravity ; and by vegetation. Transportation is performed chiefly by running water. Corrasion is per- formed by solution, and by mechanical wear. Corrasion is distinguished from weathering chiefly by including me- chanical wear among its agencies, and the importance of the distinction will be apparent when we come to consider how greatly and peculiarly this process is affected by modifying conditions. B. CONDITIONS CONTROLLING EROSION. The chief conditions which affect the rapidity of erosion are (1) declivity, (2) character of rock, and (3) climate Bate of Erosion and Declivity. In general erosion is most rapid where the slope is steepest; but weather- ing, transportation, and corrasion are affected in different ways and in differ- ent decrees. With increase of slope goes increase in the velocit}7- of running water, and with that goes increase in its power to transport undissolved detritus. The ability of a stream to corrade by solution is not notably enhanced by great velocity; but its ability to corrade by mechanical wear keeps pace with its ability to transport, or may even increase more rapidly. For not only does the bottom receive more blows in proportion as the quantity of transient detritus increases, but the blows acquire greater force from the ac- celerated current, and from the greater size of the moving fragments. It is necessary however to distinguish the ability to corrade from the rate of corrasion, which will be seen further on to depend largely on other condi- tions. CONDITIONS CONTROLLING EROSION. 103 Weathering is not directly influenced by slope, but it is reached indi- rectly through transportation. Solution and frost, the chief agents of rock decay, are both retarded by the excessive accumulation of disintegrated rock. Frost action ceases altogether at a few feet below the surface, and solution gradually decreases as the zone of its activity descends and the cir- culation on which it depends becomes more sluggish. Hence the rapid re- moval of the products of weathering stimulates its action, and especially that portion of its action which depends upon frost. If however the power of transportation is so great as to remove completely the products of weath- ering, the work of disintegration is thereby checked; for the soil which weathering tends to accumulate is a reservoir to catch rain as it reaches the earth and store it up for the work of solution and frost, instead of letting it run off at once unused. Sapping is directly favored by great declivity. In brief, a steep declivity favors transportation and thereby favors cor- rasion. The rapid, but partial, transportation of weathered rock accelerates weathering; but the complete removal of its products retards weathering. Rate of Erosion and Rvck Texture. Other things being equal, erosion is most rapid when the eroded rock offers least resistance; but the rocks which are most favorable to one portion of the process of erosion do not necessarily stand in the same relation to the others. Disintegration by solution depends in large part on the solubility of the rocks, but it proceeds most rapidly with those fragmental rocks of which the cement is soluble, and of which the texture is open. Disintegra- tion by frost is most rapid in rocks which absorb a large percentage of water and are feebly coherent. Disintegration by mechanical wear is most rapid in soft rocks. Transportation is most favored by those rocks which yield by disinte- gration the most finely comminuted debris. Rate of Erosion and Climate. The influence of climate upon erosion is less easy to formulate. The direct influences of temperature and rainfall are comparatively simple, 104 LAND SCULPTURE. but their indirect influence through vegetation is complex, and is in part opposed to the direct. Temperature affects erosion chiefly by its changes. Where the range of temperature includes the freezing point of water, frost contributes its powerful aid to weathering ; and it is only where changes are great and sudden that rocks are cracked by their unequal expansion or contraction. All the processes of erosion are affected directly by the amount of rainfall, and by its distribution through the year. All are accelerated by its increase and retarded by its diminution. When it is concentrated in one part of the year at the expense of the remainder, transportation and corrasion are accelerated, and weathering is retarded. Weathering is favored by abundance of moisture. Frost accomplishes most when the rocks are saturated ; and solution when there is the freest subterranean circulation. But when the annual rainfall is concentrated into a limited season, a larger share of the water fails to penetrate, and the gain from temporary flooding does not compensate for the checking of all solution by a long dry season. Transportation is favored by increasing water supply as greatly as by increasing declivity. When the volume of a stream increases, it becomes at the same time more rapid, and its transporting capacity gains by the in- crement to velocity as well as by the increment to volume. Hence the increase in power of transportation is more than proportional to the increase of volume. It is due to this fact chiefly that the transportation of a stream which is subject to floods is greater than it would be if its total water supply were evenly distributed in time. The indirect influence of rainfall and temperature, by means of vege- tation, has different laws. Vegetation is intimately related to water supply. There is little or none where the annual precipitation is small, and it is profuse where the latter is great — especially where the temperature is at the same time high. In proportion as vegetation is profuse the solvent power of percolating water is increased, and on the other hand the ground is sheltered from the mechanical action of rains and rills. The removal of disintegrated rock is greatly impeded by the conservative power of roots CONSERVATIVE INFLUENCE OF VEGETATION. 105 and fallen leaves, and a soil is thus preserved. Transportation is retarded. Weathering by solution is accelerated up to a certain point, but in the end it suffers by the clogging- of transportation. The work of frost is nearly stopped as soon as the depth of soil exceeds the limit of frost action. The force of rain drops is expended on foliage. Moreover a deep soil acts as a distributing reservoir for the water of rains, and tends to equalize the flow of streams. Hence the general effect of vegetation is to retard erosion ; and since the direct effect of great rainfall is the acceleration of erosion, it results that its direct and indirect tendencies are in opposite directions. In arid regions of which the declivities are sufficient to give thorough drainage, the absence of vegetation is accompanied by absence of soil. When a shower falls, nearly all the water runs off from the bare rock, and the little that is absorbed is rapidly reduced by evaporation. Solution be- comes a slow process for lack of a continuous supply of water, and frost accomplishes its work only when it closely follows the infrequent rain. Thus weathering is retarded. Transportation has its work so concentra- ted by the quick gathering of showers into floods, as to compensate, in part at least, for the smallness of the total rainfall from which they derive their power. Hence in regions of small rainfall, surface degradation is usually lim- ited by the slow rate of disintegration; while in regions of great rainfall it is limited by the rate of transportation. There is probably an intermediate condition with moderate rainfall, in which a rate of disintegration greater than that of an arid climate is balanced by a more rapid transportation than consists with a very moist climate, and in which the rate of degradation at- tains its maximum. Over nearly the whole of the earth's surface there is a soil, and wher- ever this exists we know that the conditions are more favorable to weather- ing than to transportation. Hence it is true in general that the conditions which limit transportation are those which limit the general degradation of the surface. To understand the manner in which this limit is reached it is necessary to look at the process by which the work is accomplished. 106 LAND SCULPTURE. Transportation and Comminution. A stream of water flowing down its bed expends an amount of energy that is measured by the quantity of water and the vertical distance through which it descends. If there were no friction of the water upon its channel the velocity of the current would continually increase; but if, as is the usual case, there is no increase of velocity, then the whole of the energy is consumed in friction. The friction produces inequalities in the motion of the water, and especially induces subsidiary currents more or less oblique to the general onward movement. Some of these subsidiary currents have an upward tendency, and by them is performed the chief work of transpor- tation. They lift small particles from the bottom and hold them in suspen- sion while they move forward with the general current. The finest particles sink most slowly and are carried farthest before they fall. Larger ones are barely lifted, and are dropped at once. Still larger are only half lifted; that is, they are lifted on the side of the current and rolled over without quitting the bottom. And finally there is a limit to the power of every cur- rent, and the largest fragments of its bed are not moved at all. There is a definite relation between the velocity of a current and the size of the largest bowlder it will roll. It has" been shown by Hopkins that the weight of the bowlder is j^roportioned to the sixth power of the velocity. It is easily shown also that the weight of a suspended particle is propor- tioned to the sixth power of the velocity of the upward current that will pre- vent its sinking. But it must not be inferred that the total load of detritus that a stream will transport bears any such relation to the rapidity of its current. The true inference is, that the velocity determines the size-limit of the detritus that a stream can move by rolling, or can hold in suspension. Every particle which a stream lifts and sustains is a draft upon its energy, and the measure of the draft is the weight (weighed in water) of the particle, multiplied by the distance it would sink in still water in the time during which it is suspended. If for the sake of simplicity we suppose the whole load of a stream to be of uniform particles, then the measure of the energy consumed in their transportation is their total weight multiplied by the distance one of them would sink in the time occupied in their transpor- COMMINUTION. 107 tation. Since fine particles sink more slowly than coarse, the same con- sumption of energy will convey a greater load of fine than of coarse. Again, the energy of a clear stream is entirely consumed in the friction of flow; and the friction bears a direct relation to its velocity. But if de- tritus be added to the water, then a portion of its energy is diverted to the transportation of the load; and this is done at the expense of the friction of flow, and hence at the expense of velocity. As the energy expended in transportation increases, the velocity diminishes. If the detritus be com- posed of uniform particles, then we may also say that as the load increases the velocity diminishes. But the diminishing velocity will finally reach a point at which it can barely transport particles of the given size, and when this point is attained, the stream has its maximum load of detritus of the given size. But fine detritus requires less velocity for its transportation than coarse, and will not so soon reduce the current to the limit of its effi- ciency. A greater percentage of the total energy of the stream can hence be employed by fine detritus than by coarse. (It should be explained that the friction of flow is in itself a complex affair. The water in contact with the bottom and walls of the channel de- velops friction by flowing past them, and that which is farther away by flowing past that which is near. The inequality of motion gives rise to cross currents and there is a friction of these upon each other. The ratio or co- efficient of friction of water against the substance of the bed, the coefficient of friction of water against water, or the viscosity of water, and the form of the bed, all conspire to determine the resistance of flow and together make up what may be called the coefficient of the friction of flow. The friction depends on its coefficient and on the velocity.) Thus the capacity of a stream for transportation is enhanced by com- minution in two ways. Fine detritus, on the one hand, consumes less energy for the transportation of the same weight, and on the other, it can utilize a greater portion of the stream's energy. It follows, as a corollary, that the velocity of a fully loaded stream de- pends (ceteris paribus) on the comminution of the material of the load. When a stream has its maximum load of fine detritus, its velocity will be 108 LAND SCULPTURE. less than when carrying its maximum load of coarse detritus; and the greater load corresponds to the less velocity. It follows also that a stream which is supplied with heterogeneous debris will select the finest. If the finest is sufficient in quantity the cur- rent will be so checked by it that the coarser cannot be moved. If the finest is not sufficient the next grade will be taken, and so on. Transportation and Declivity. To consider now the relation of declivity to transportation we will as- sume all other conditions to be constant. Let us suppose that two streams have the same length, the same quantity of water, flow over beds of the same character, and are supplied to their full capacities with detritus of the same kind; but differ in the total amount of fall. Their declivities or rates of fall are proportional to their falls. Since the energy of a stream is meas- ured by the product of its volume and its fall, the relative energies of the two streams are proportional to their falls, and hence proportional to their declivities. The velocities of the two streams, depending, as we have seen above, on the character of the detritus which loads them, are the same; and hence the same amount of energy is consumed by each in the friction of flow. And since the energy which each stream expends in transportation is the residual after deducting what it spends in friction from its total energy, it is evident that the stream with the greater declivity will not merely have the greater energy, but will expend a less percentage of it in friction and a greater percentage in transportation. Hence declivity favors transportation in a degree that is greater than its simple ratio. There are two elements of which no account is taken in the preceding discussion, but which need to be mentioned to prevent misapprehension, although they detract in no way from the conclusions. The first is the addition which the transported detritus makes to the energy of the stream. A stream of water charged with detritus is at once a compound and an unstable fluid. It has been treated merely as an un- stable fluid requiring a constant expenditure of energy to maintain its con- DECLIVITY AIDS TRANSPORTATION. 109 stitution ; but looking at it as a compound fluid, it is plain that the energy it develops by its descent is greater than the energy pertaining to the water alone, in the precise ratio of the mass of the mixture to the mass of the sim- ple water. The second element is the addition which the detritus makes to the friction of flow. The coefficient of friction of the compound stream upon its bottom will always be greater than that of the simple stream of water, and the coefficient of internal friction or the viscosity will be greater than that of pure water, and hence for the same velocity a greater amount of energy will be consumed. It may be noted in passing, that the energy which is consumed in the friction of the detritus on the stream bed, accomplishes as part of its work the mechanical corrasion of the bed. Transportation and Quantity of Water. A stream's friction of flow depends mainly on the character of the bed, on the area of the surface of contact, and on the velocity of the current. When the other elements are constant, the friction varies approximately with the area of contact. The area of contact depends on the length and form of the channel, and on the quantity of water. For streams of the same length and same form of cross-section, but differing in size of cross-section, the area of contact varies directly as the square root of the quantity of water. Hence, ceteris paribus, the friction of a stream on its bed is proportioned to the square root of the quantity of water. But as stated above, the total energy of a stream is proportioned directly to the quantity of water; and the total energy is equal to the energy spent in friction, plus the energy spent in transportation. Whence it follows that if a stream change its quan- tity of water without changing its velocity or other accidents, the total energy will change at the same rate as the quantity of water; the energy spent in friction will change at a less rate, and the energy remaining for transportation will change at a greater rate. Hence increase in quantity of water favors transportation in a degree that is greater than its simple ratio. It follows as a corollary that the running water which carries the debris 110 LAND SCULPTURE. of a district loses power by subdivision toward its sources; and that, unless there is a compensating increment of declivity, the tributaries of a river will fail to supply it with the full load it is able to carry. It is noteworthy also that the obstruction which vegetation opposes to transportation is especially effective in that it is applied at the infinitesimal sources of streams, where the force of the running water is least. A stream which can transport debris of a given size, may be said to be competent to such debris. Since the maximum particles which streams are able to move are proportioned to the sixth powers of their velocities, com- petence depends on velocity. Velocity, in turn, depends on declivity and volume, and (inversely) on load. In brief, the capacity of a stream for transportation is greater for fine debris than for coarse. Its capacity for the transportation of a given kind of debris is enlarged in more than simple ratio by increase of declivity; and it is enlarged in more than simple ratio by increase of volume. The competence of a stream for the transport of debris of a given fine- ness, is limited by a corresponding velocity. The rate of transportation of debris of a given fineness may equal the capacity of the transporting stream, or it may be less. When it is less, it is always from the insufficiency of supply. The supply furnished by weathering is never available unless the degree of fineness of the debris brings it within the competence of the stream at the point of supply. The chief point of supply is at the very head of the flowing water. The rain which falls on material that has been disintegrated by weathering, begins after it has saturated the immediate surface to flow off. But it forms a very thin sheet ; its friction is great ; its velocity is small ; and it is com- petent to pick up only particles of exceeding fineness. If the material is heterogeneous, it discriminates and leaves the coarser particles. As the sheet moves on it becomes deeper and soon begins to gather itself into rills. As the deepening and concentration of water progresses, either its capacity increases and the load of fine particles is augmented, or, if fine particles are not in sufficient force, its competence increases, and larger CORRASION VERSUS TRANSPORTATION. Ill ones are lifted. In either case the load is augmented, and as rill joins rill it steadily grows, until the accumulated water finally passes beyond the zone of disintegrated material. The particles which the feeble initial currents are not competent to move, have to wait either until they are subdivided by the agencies of weathering, or until the deepening of the channels of the rills so far increases the declivities that the currents acquire the requisite ve- locity, or until some fiercer storm floods the ground with a deeper sheet of water. Thus rate of transportation, as well as capacity for transportation, is favored by fineness of debris, by declivity, and by quantity of water. It is opposed chiefly by vegetation, which holds together that which is loosened by weathering, and shields it from the agent of transportation in the very place where that agent is weakest. When the current of a stream gradually diminishes in its course — as for example in approaching the ocean — the capacity for transportation also diminishes ; and so soon as the capacity becomes less than the load, pre- cipitation begins — the coarser particles being deposited first. Corrasion and Transportation. Where a stream has all the load of a given degree of comminution which it is capable of carrying, the entire energy of the descending water and load is consumed in the translation of the water and load and there is none applied to corrasion. If it has an excess of load its velocity is thereby diminished so as to lessen its competence and a portion is dropped. If it has less than a full load it is in condition to receive more and it corrades its bottom. A fully loaded stream is on the verge between corrasion and deposition. As will be explained in another place, it may wear the walls of its channel, but its wear of one wall will be accompanied by an addition to the opposite wall. The work of transportation may thus monopolize a stream to the exclu- sion of corrasion, or the two works may be carried forward at the same time. 112 LAND SCULPTURE. Corrasion and Declivity. The rapidity of mechanical corrasion depends on the hardness, size, and number of the transient fragments, on the hardness of the rock-bed, and on the velocity of the stream. The blows which the moving fragments deal upon the stream-bed are hard in proportion as the fragments are large and the current is swift. They are most effective when the fragments are hard and the bed-rock is soft. They are more numerous and harder upon the bottom of the channel than upon the sides because of the constant tendency of the particles to sink in water. Their number is increased up to a certain limit by the increase of the load of the stream ; but when the fragments become greatly crowded at the bottom of a stream their force is partially spent among themselves, and the bed-rock is in the same degree protected. For this reason, and because increase of load causes retardation of current, it is probable that the maximum wTork of corrasion is performed when the load is far within the transporting capacity. The element of velocity is of double importance since it determines not only the speed, but to a great extent the size of the pestles which grind the rocks. The coefficients upon which it in turn depends, namely, declivity and quantity of water, have the same importance in corrasion that they have in transportation. Let us suppose that a stream endowed with a constant volume of water, is at some point continuously supplied with as great a load as it is capable of canying. For so great a distance as its velocity remains the same, it will neither corrade (downward) nor deposit, but will leave the grade of its bed unchanged. But if in its progress it reaches a place where a less declivity of bed gives a diminished velocity, its capacity for transportation will be- come less than the load and part of the load will be deposited. Or if in its progress it reaches a place where a greater declivity of bed gives an in- creased velocity, the capacity for transportation will become greater than the load and there will be corrasion of the bed. In this way a stream which has a supply of debris equal to its capacity, tends to build up the gentler slopes of its bed and cut away the steeper. It tends to establish a single, uniform grade. DECLIVITY AND VOLUME. 113 Let us now suppose that the stream after having obliterated all the in- equalities of the grade of its bed loses nearly the whole of its load. Its velocity is at once accelerated and vertical corrasion begins through its whole length. Since the stream has the same declivity and consequently the same velocity at all points, its capacity for corrasion is everywhere the same. Its rate of corrasion however will depend on the character of its bed. Where the rock is hard corrasion will be less rapid than where it is soft, and there will result inequalities of grade. But so soon as there is inequality of grade there is inequality of velocity, and inequality of capacity for corra- sion; and where hard rocks have produced declivities, there the capacity for corrasion will be increased. The differentiation will proceed until the ca- pacity for corrasion is everywhere proportioned to the resistance, and no further, — that is, until there is an equilibrium of action. In general, we may say that a stream tends to equalize its work in all parts of its course. Its power inheres in its fall, and each foot of fall has the same power. When its work is to corrade and the resistance is unequal, it concentrates its energy where the resistance is great by crowding many feet of descent into a small space, and diffuses it where the resistance is small by using but a small fall in a long distance. When its work is to transport, the resistance is constant and the fall is evenly distributed by a uniform grade. When its work includes both transportation and corrasion, as in the usual case, its grades are somewhat unequal; and the inequality is greatest when the load is least. It is to be remarked that in the case of most streams it is the flood stage which determines the grades of the channel. The load of detritus is usually greatest during the highest floods, and power is conferred so rapidly with increase of quantity of water, that in any event the influence of the stream during its high stage will overpower any influence which may have been exerted at a low stage. That relation of transportation to corrasion which subsists when the water is high will determine the grades of the water-way. Declivity and Quantity of Water. The conclusions reached in regard to the relations of corrasion and de- clivity depend on the assumption that the volume of the stream is the same 8 H M 114 LAND SCULPTURE. throughout its whole course, and they consequently apply directly to such portions only of streams as are not increased by tributaries. A 'simple mod- ification will include the more general case of branching streams. Let us suppose that two equal streams which join, have the same de- clivity, and are both fully loaded with detritus of the same kind. If the channel down which they flow after union has also the same declivity, then the joint stream will have a greater velocity than its branches, its capacity for transportation will be more than adequate for the joint load, and it will corrade its bottom. By its corrosion it will diminish the declivity of its bed, and consequently its velocity and capacity for transportation, until its ca- pacity is equal to the total capacity of its tributaries. When an equilibrium of action is reached, the declivity of the main stream will be less than the declivities of its branches. This result does not depend on the assumed equality of the branches, nor upon their number. It is equally true that in any river system which is fully supplied with material for transportation and which has attained a condition of equal action, the declivity of the smaller streams is greater than that of the larger. Let us further suppose that two equal streams which join, are only par- tially loaded, and are corrading at a common rate a common rock. If the channel down which they flow after union is in the same rock and has the same declivity, then the joint river will have a greater velocity, and will corrade more rapidly than its branches. By its more rapid corrasion it will diminish the declivity of its bed, until as before there is an equilibrium of action, — the branch having a greater declivity than the main. This result also is independent of the number and equality of the branches: and it is equally true that in any river system which traverses and corrades rock of equal resistance throughout, and which has reached a condition of equal action, the declivity of the smaller streams is greater than that of the larger. In general we may say that, ceteris paribus, declivity hears an inverse re- lation to quantity of water. (There is an apparent exception to this law, which is specially note- worthy in the sculpture of bad-lands, and will be described in another place). TOE LAW OF STRUCTURE. 115 II. SCULPTURE. Erosion may be regarded from several points of view. It lays bare rocks which were before covered and concealed, and is thence called denu- dation. It reduces the surfaces of mountains, plateaus, and continents, and is thence called degradation. It carves new forms of land from those which before existed, and is thence called land sculpture. In the following pages it will be considered as land sculpture, and attention will be called to cer- tain principles of erosion which are concerned in the production of topo- graphic forms. Scidpture and Declivity. We have already seen that erosion is favored by declivity. Where the declivity is great the agents of erosion are powerful; where it is small they are weak; where there is no declivity they are powerless. Moreover it has been shown that their power increases with the declivity in more than sim- ple ratio. It is evident that if steep slopes are worn more rapidly than gentle, the tendency is to abolish all differences of slope and produce uniformity. The law of uniform slope thus opposes diversity of topography, and if not com- plemented by other laws, would reduce all drainage basins to plains. But in reality it is never free to work out its full results; for it demands a uni- formity of conditions which nowhere exists. Only a water sheet of uniform depth, flowing over a surface of homogeneous material, would suffice; and every inequality of water depth or of rock texture produces a correspond- ing inequality of slope and diversity of form. The reliefs of the landscape exemplify other laws, and the law of uniform slopes is merely the conserva- tive element which limits their results. Sculpture and Structure ; the Law of Structure. We have already seen that erosion is influenced by rock character. Certain rocks, of which the hard are most conspicuous, oppose a stubborn resistance to erosive agencies ; certain others, of which the soft are most conspicuous, oppose a feeble resistance. Erosion is most rapid where the resistance is least, and hence as the soft rocks are worn away the 116 LAND SCULPTURE. hard are left prominent. The differentiation continues until an equi- librium is reached through the law of declivities. When the ratio of ero- sive action as dependent on declivities becomes equal to the ratio of resist- ances as dependent on rock character, there is equality of action. In the structure of the earth's crust hard and soft rocks are grouped with infinite diversity of arrangement. They are in masses of all forms, and dimensions, and positions ; and from these forms are carved an infinite variety of topo- graphic reliefs. In so far as the law of structure controls sculpture, hard masses stand as eminences and soft are carved in valleys. The Law of Divides. We have seen that the declivity over which water flows bears an in- verse relation to the quantity of water. If we follow a stream from its mouth upward and pass successively the mouths of its tributaries, we find its volume gradually less and less and its grade steeper and steeper, until finally at its head we reach the steepest grade of all. If we draw the pro- file of the river on paper, we produce a curve concave upward and with the greatest curvature at the upper end. The same law applies to every tribu- tary and even to the slopes over which the freshly fallen rain flows in a sheet before it is gathered into rills. The nearer the water-shed or divide the steeper the slope; the farther away the less the slope. It is in accordance with this law that mountains are steepest at their crests. The profile of a mountain if taken along drainage lines is concave outward as represented in the diagram; and this is purely a matter of sculp- ture, the uplifts from which mountains are carved rarely if ever assuming this form. Fig. 54. — Typical profile of the Drainage Slopes of Mountains. Under the law of Structure and the law of Divides combined, the fea- tures of the earth are carved. Declivities are steep in proportion as their material is hard; and they are steep in proportion as they are near divides. THE LAW OF DIVIDES. 117 The distribution of hard and soft rocks, or the geological structure, and the distribution of drainage lines and water-sheds, are coefficient conditions on which depends the sculpture of the land. In the sequel it will be shown that the distribution of drainage lines and water-sheds depends in part on that of hard and soft rocks. In some places the first of the two conditions is the more important, in others the second. In the bed of a stream without tributaries the grade de- pends on the structure of the underlying rocks. In rock which is homo- geneous and structureless all slopes depend on the distribution of divides and drainage lines. The relative importance of the two conditions is especially affected by climate, and the influence of this factor is so great that it may claim rank as a third condition of sculpture. Sculpture and Climate. The Henry Mountains consist topographically of five individuals, separated by low passes, and practically independent in climate. At the same time they are all of one type of structure, being constituted by similar aggregation of hard and soft rocks. Their altitudes appear in the following table. Altitude above the sea. Mount Ellen ; . 11, 250 feet. Mount Pennell J 1, 150 feet. Mount Hillers 10, 500 feet. Mount Ellsworth 8, 000 feet. Mount Holmes 7, 775 feet. The plain on which they stand has a mean altitude of 5,500 feet, and is a desert. A large proportion of the rain which falls in the region is caught by the mountains, and especially by the higher mountains. Of this there is abundant proof in the distribution of vegetation and of springs. The vegetation of the plain is exceedingly meager, comprising only sparsely set grasses and shrubs, and in favored spots the dwarf cedar of the West (Juniperus occidentalis). 118 LAND SCULPTURE. Mount Ellen, which has a continuous rid^e two miles lorn? and more than 11,000 feet high, bears cedar about its base, mingled higher up with pinon (JPinus edidis), and succeeded above by the yellow pine (P. xoon- derosa), spruce (Abies Doiiglasii), fir (A. Engelmanni), and aspen (Popidus tremidoides). The pines are scattering, but the cedars are close set, and the firs are in dense groves. The upper slopes where not timbered are matted with luxuriant grasses and herbs. The summits are naked. Mount Pennell sends a single peak only to the height of the Ellen ridge. Its vegetation is nearly the same, but the timber extends almost to the summit. Mount Hillers is G50 feet lower. Its timber reaches to the principal summit, but is less dense than on the higher mountains. The range of trees is the same. Mount Ellsworth, 2,500 feet lower than Mount Hillers, bears neither fir, spruce, pine nor aspen. Cedar and pifion climb to the summit, but are not so thickly set as on the lower slopes of the larger mountains. The grasses are less rank and grow in scattered bunches. Mount Holmes, a few feet lower, has the same flora, with the addition of a score of spruce trees, high up on the northern flank. Its summits are bare. In a word, the luxuriance of vegetation, and the annual rainfall, of which it is the index, are proportioned to the altitude. Consider now the forms of the mountain tops. In Figure 55 are pictured the summit forms of Mount Ellen. The crests are rounded; the slopes are uniform and smooth. Examination has shown that the constituent rocks are of varying degrees of hardness, trachyte dikes alternating with sandstones and shales; but these variations rarely find expression in the sculptured forms. In Figure 56 are the summit crags of Mount Holmes. They are dikes of trachyte denuded by a discriminating erosion of their encasements of sandstone, and carved in bold relief. In virtue of their superior hardness they survive the general degradation. The other mountains are intermediate in the character of their sculpture,. Mount Pennell is nearly as smooth as Mount Ellen. Mount Ellsworth is Fig. 55. — The Crest^of Mount Ellen, as seen from Ellen Peak. Fig. F6. — The Crest of Mount Holmes. THE INFLUENCE OF CLIMATE. 1 H) nearly an rugged as Mount Holmes. One may ride to the crest of Mount Ellen and to the summit of Mount Pennell; lie may lead his sure-footed cayuse to the top of Mount Hillers; but Mounts Ellsworth and Holmes are not to be scaled by horses. The mountaineer must climb to reach their summits, and for part of the way use hands as well as feet. In a word, the ruggedness of the summits or the differentiation of hard and soft by sculpture, is proportioned inversely to the altitude. And rainfall, which in these mountains depends directly on altitude, is propor- tioned inversely to ruggedness. Hie explanation of this coincidence depends on the general relations of vegetation to erosion. We have seen that vegetation favors the disintegration of rocks and retards the transportation of the disintegrated material. Where vegetation is profuse there is always an excess of material awaiting transportation, and the limit to the rate of erosion comes to be merely the limit to the rate of transportation. And since the diversities of' rock texture, such as hard- ness and softness, affect only the rate of disintegration (weathering and corrasion) and not the rate of transportation, these diversities do not affect the rate of erosion in regions of profuse vegetation, and do not produce corresponding diversities of form. On the other hand, where vegetation is scant or absent, transportation and corrasion are favored, while weathering is retarded. There is no accumu- lation of disintegrated material. The rate of erosion is limited by the rate of weathering, and that varies with the diversity of rock texture. The soft are eaten away faster than the hard; and the structure is embodied in the topographic forms. Thus a moist climate by stimulating vegetation produces a sculpture independent of diversities of rock texture, and a dry climate by repressing vegetation produces a sculpture dependent on those diversities. With great moisture the law of divides is supreme; with aridity, the law of struc- ture. Hence it is that the upper slopes of the loftier of the Henry Mountains are so carved as to conceal the structure, while the lower slopes of the same mountains and the entire forms of the less lofty mountains are so carved 120 LAND SCULPTURE. as to reveal the structure; and hence too it is that the arid plateaus of the Colorado Basin abound in cliffs and canons, and offer facilities to the student of geological structure which no humid region can afford. Here too is the answer to the question so often asked, "whether the rains and rivers which excavated the canons and carved the cliffs were not mightier than the rains and rivers of to-day." Aridity being an essential condition of this peculiar type of sculpture, we may be sure that through long ages it has characterized the climate of the Colorado Basin. A climate of great rainfall, as Professor Powell has already pointed out in his "Ex- ploration of the Colorado," would have produced curves and gentle slopes in place of the actual angles and cliffs. Bad-lands. Mountain forms in general depend more on the law of divides than on the law of structure, but their independence of structure is rarely perfect, and it is difficult to discriminate the results of the two principles. For the investigation of the workings of the law of divides it is better to select examples from regions which afford no variety of rock texture and are hence unaffected in their erosion by the law of structure. Such examples are found in bad-lands. Where a homogeneous, soft rock is subjected to rapid degradation in an arid climate, its surface becomes absolutely bare of vegetation and is carved into forms of great regularity and beauty. In the neighborhood of the Henry Mountains, the Blue Gate and Tununk shales are of this character, and their exposures afford many opportunities for the study of the principles of sculpture. I was able to devote no time to them, but in riding across them my attention was attracted by some of the more striking features, and these I will venture to present, although I am conscious that they form but a small part of the whole material which the bad-lands may be made to yield. If we examine a bad-land ridge, separating two drainage lines and forming a divide between them, we find an arrangement of secondary ridges and secondary drainage lines, similar to that represented in the diagram, (Figure 58.) 9 O 2 t c CD 0) M 'J-. (I C O BADLANDS. 121 The general course of the main ridge being straight, its course in detail is found to bear a simple relation to the secondary ridges. Wherever a sec- ondary joins, the main ridge turns, its angle being directly toward the second- ary. The divide thus follows a zigzag course, being deflected to the right or left by each lateral spur. The altitude of the main ridge is correspondingly related to the sec- ondary ridges. At every point of union there is a maximum, and in the intervals are saddles. The maxima are not all equal, but bear some relation to the magnitudes of the corresponding secondary ridges, and are especially accented where two or more secondaries join at the same point. (See profile in Figure 59.) I conceive that the explanation of these phenomena is as follows: The heads of the secondarv drainage lines laid down in the diagram are in nature tolerably definite points. The water which during rain converges at one of these points is there abruptly concentrated in volume. Above the point it is a sheet, or at least is divided into many rills. Below it, it is a single stream with greatly increased power of transportation and corrasion. The principle of equal action gives to the concentrated stream a less declivity than to the diffused sheet, and — what is especially important — it tends to pro- duce an equal grade in all directions upward from the point of convergence. The converging surface becomes hopper-shaped or funnel-shaped; and as the point of convergence is lowered by corrasion, the walls of the funnel are eaten back equally in all directions — except of course the direction of the stream. The influence of the stream in stimulating erosion above its head is thus extended radially and equally through an arc of 180°, of which the center is at the point of convergence. Where two streams head near each other, the influence of each tends to pare away the divide between them, and by paring to carry it farther back. The position of the divide is determined by the two influences com- bined and represents the line of equilibrium between them. The influences being radial from the points of convergence, the line of equilibrium is tangential, and is consequently at right angles to a line connecting the two points. Thus, for example, if «, b, and c (Figure 58) are the points of con- vergence at the heads of three drainage lines, the divide line ed is at right 122 LAND SUULPTUKE. angles to a line connecting a and b, and the divides fd and gd are simi- larly determined. The point d is simnlta- taneously determined by the intersection of the three divide lines. Furthermore, since that point of the line ed which lies directly between a and b is near- est to those points, it is the point of the divide most subject to the erosive influences which radiate from a and b, and it is consequently degraded lower than the contiguous portions of the divide. The points d and e are less re- duced ; and d, which can be shown by similar reasoning to stand higher than the adjacent portion of either of the three ridges which there unite, is a local maximum. There is one other peculiarity of bad-land Fig. 58.— Ground-plan of a Bad-laud > . . Eidge, showing its relation to Water- forms which is of great significance, but which ways. The smooth lines represent Tin ±1 i ~i j. i l • Diyides * 1 shall nevertheless not undertake to explain. Fig. 59.— Profile of the same ridge. According to the law of divides, as stated in a previous paragraph, the profile of any slope in bad-lands should be con- cave upward, and the slope should be steepest at the divide. The union or intersection of two slopes on a divide should produce an angle. But in point of fact the slopes do not unite in an angle. They unite in a curve, and the profile of a drainage slope instead of being concave all the way to its summit, changes its curvature and becomes convex. Figure GO rep- resents a profile from a to b of Figure 58. From a to m and from b to n the slopes are concave, but from m to n there is a convex curvature. Where the flanking slopes are as steep as represented in the diagram, the con- vexity on the crest of a ridge has a breadth of only two or three yards, but where the flanking slopes are gentle, its breadth is several times as great. It is never absent. Thus in the sculpture of the bad-lands there is revealed an exception to the law of divides, — an exception which cannot be referred to accidents INTERDEPENDENCE OF DRAINAGE SLOPES. 123 of structure, and which is as persistent in its recurrence as are the features which conform to the law, — an exception which in some unexplained way is part of the law. Our analysis of the agencies and conditions of erosion, on the one hand, has led to the conclusion that (where structure does not pre- Fig. GO. — Cross- profile of a Bad-land Divide. vent) the declivities of a continuous drainage slope increase as the quantities of water flowing over them decrease ; and that they are great in proportion as they are near divides. Our observation, on the other hand, shows that the declivities increase as the quantities of water diminish, up to a certain point where the quantity is very small, and then decrease ; and that declivities are great in proportion as they are near divides, unless they are very near divides. Evidently some factor has been overlooked in the analysis, — a factor which in the main is less important than the flow of water, but which asserts its existence at those points where the flow of water is exceedingly small, and is there supreme. Equal Action and Interdependence. The tendency to equality of action, or to the establishment of a dy- namic equilibrium, has already been pointed out in the discussion of the principles of erosion and of sculpture, but one of its most important results has not been noticed. Of the main conditions which determine the rate of erosion, namely, quantity of running water, vegetation, texture of rock, and declivity, only the last is reciprocally determined by rate of erosion. Declivity originates in upheaval, or in the displacements of the earth's crust by which mountains and continents are formed ; but it receives its distribution in detail in accordance with the laws of erosion. Wherever by reason of change in any of the condi- tions the erosive agents come to have locally exceptional power, that power is# 124 LAND SCDLPTUEE. steadily diminished by the reaction of rate of erosion upon declivity. Every slope is a member of a series, receiving the water and the waste of the slope above it, and discharging its own water and waste upon the slope below. If one member of the series is eroded with exceptional rapidity, two things immediately result : first, the member above has its level of discharge lowered, and its rate of erosion is thereby increased ; and second, the mem- ber below, being clogged by an exceptional load of detritus, has its rate of erosion diminished. The acceleration above and the retardation below, diminish the declivity of the member in which the disturbance originated ; and as the declivity is reduced the rate of erosion is likewise reduced. But the effect does not stop here. The disturbance which has been transferred from one member of the series to the two which adjoin it, is by them transmitted to others, and does not cease until it has reached the con- fines of the drainage basin. For in each basin all lines of drainage unite in a main line, and a disturbance upon any line is communicated through it to the main line and thence to every tributary. And as any member of the system may influence all the others, so each member is influenced by every other. There is an interdependence throughout the system. IIL-SYSTEMS OF DRAINAGE. To know well the drainage of a region two systems of lines must be ascertained — the drainage lines and the divides. The maxima of surface on which waters part, and the minima of surface in which waters join, are alike intimately associated with the sculpture of the earth and with the his- tory of the earth's structure ; and the student of either sculpture or history can well afford to study them. In the following pages certain conditions which affect their permanence and transformations are discussed. THE STABILITY OF DRAINAGE LINES. In corrasion the chief work is performed by the impact and friction of hard and heavy particles moved forward by running water. They are driven against all sides of the channel, but their tendency to sink in water brings them against the bottom with greater frequency and force than against the walls. If the rate of wear be rapid, by far PONDING. 125 the greater part of it is applied to the bottom, and the downward corra- sion is so much more powerful than the lateral that the effect of the latter is practically lost, and the channel of the stream, without varying the posi- tion of its banks, carves its way vertically into the rock beneath. It is only when corrasion is exceedingly slow that the lateral wear becomes of importance ; and hence as a rule the position of a stream bed is permanent. The stability of drainage lines is especially illustrated in regions of displacement. If a mountain is slowly lifted athwart the course of a stream, the corrasion of the latter is accelerated by the increase of declivity, and instead of being turned aside by the uplift, it persistently holds its place and carves a channel into the mountain as the mountain rises. For exam- ple the deep clefts which intersect the Wasatch range owe their existence to the fact that at the time of the beginning of the uplift which has made the range, there were streams flowing across the line of its trend which were too powerful to be turned back by the growing ridge. The same relation has been shown by Professor Powell where the Green River crosses the uplift of the Uinta Mountains, and in many instances throughout the Rocky Mountain region it may be said that rivers have cut their way through mountains merely because they had established their courses before the inception of the displacement, and could not be diverted by an obstruction which was thrown up with the slowness of mountain uplift. THE INSTABILITY OF DRAINAGE DINES. The stability of waterways being the rule, every case of instability requires an explanation; and in the study of such exceptional cases there have been found a number of different methods by which the courses of streams are shifted. The more important will be noted. Ponding. When a mountain uplift crosses the course of a stream, it often hap- pens that the rate of uplift is too rapid to be equaled by the corrasion of the stream, and the uprising rock becomes a dam over which . the water still runs, but above which there is accumulated a pond or lake. Whenever this takes place, the pond catches all the debris of the upper ■V" 126 LAND SCULPTURE. course of the stream, and the water which overflows at the outlet having been relieved of its load is almost powerless for corrasion, and cannot con- tinue its contest with the uplift unless the pond is silted up with detritus. As the uplift progresses the level of the pond is raised higher and higher, until finally it finds a new outlet at some other point. The original outlet is at once abandoned, and the new one becomes a permanent part of the course of the stream. As a rule it is only large streams which hold their courses while mountains rise; the smaller are turned back by ponding, and are usually diverted so as to join the larger. The disturbances which divert drainage lines are not always of the sort which produce mountains. The same results may follow the most gentle undulations of plains. It required a movement of a few feet only to change the outlet of Lakes Michigan, Huron, and Superior from the Illinois River to the St. Clair; and in the tilting which turned Lake Winipeg from the Mississippi to the Nelson no abrupt slopes were produced. If the entire history of the latter case were worked out, it would probably appear that the Saskatchewan River which rises in the Rocky Mountains beyond our northern boundary, was formerly the upper course of the Mississippi, and that when, by the rising of land in Minnesota or its sinking at the north, a barrier was formed, the water was ponded and Lake Winipeg came into existence. By the continuance of the movement of the land the lake was increased until it overflowed into Hudson's Bay; and by its further continuance, combined with the corrasion of the outlet, the lake has been again diminished. When eventually the lake disappears the revolution will be complete, and the Saskatchewan will flow directly to Hudson's Bay, as it once flowed directly to the Gulf of Mexico. (See the "Physical Fea- tures of the Valley of the Minnesota River," by General G, K. Warren.) Planation. It has been shown in the discussion of the relations of transporta- tion and corrasion that downward wear ceases when the load equals the capacity for transportation. Whenever the load reduces the downward corrasion to little or nothing, lateral corrasion becomes relatively and actu- ally of importance. The first result of the wearing of the walls of a stream's PLANATION. 127 channel is the formation of a flood-plain. As an effect of momentum the current is always swiftest along the outside of a curve of the channel, and it is there that the wearing is performed ; while at the inner side of the curve the current -is so slow that part of the load is deposited. In this way the width of the channel remains the same while its position is shifted, and every part of the valley which it has crossed in its shiftings comes to be covered by a deposit which does not rise above the highest level of the water. The surface of this deposit is hence appropriately called the flood-plain of the stream. The deposit is of nearly uniform depth, descending no lower than the bottom of the water-channel, and it rests upon a tolerably even surface of the rock or other material which is corraded by the stream. The process of carving away the rock so as to- produce an even surface, and at the same time covering it with an alluvial deposit, is the process oi pi dila- tion. It sometimes happens that two adjacent streams by extending their areas of planation eat through the dividing ridge and join their channels. The stream which has the higher surface at the point of contact, quickly abandons the lower part of its channel and becomes a branch of the other, having shifted its course by planation. The slopes of the Henry Mountains illustrate the process in a pecu- liarly striking manner. The streams which flow down them are limited in their rate of degradation at both ends. At their sources, erosion is opposed by the hardness of the rocks ; the trachytes and metamorphics of the mountain tops are carved very slowly. At their mouths, they discharge into the Colorado and the Dirty Devil, and cannot sink their channels more rapidly than do those rivers. Between the mountains and the rivers, they cross rocks which are soft in comparison with the trachyte, but they can deepen their channels with no greater rapidity than at their ends. The grades have adjusted themselves accordingly. Among the hard rocks of the mountains the declivities are great, so as to give efficiency to the eroding water. Among the sedimentary rocks of the base they are small in com- parison, the chief work of the streams being the transportation of the tra- chyte debris. So greatly are the streams concerned in transportation, and so little in downward corrasion (outside the trachyte region), that their 128 LAND SCULPTURE. grades are almost unaffected by the differences of rock texture, and they pass through sandstone and shale with nearly the same declivity. The rate of downward corrasion being thus limited by extraneous con- ditions, and the instrument of corrasion — the debris of the hard trachyte — being efficient, lateral corrasion is limited only by the resistance which the banks of the streams oppose. Where the material of the banks is a firm sand- stone, narrow flood-plains are formed ; and where it is a shale, broad ones. In the Gray Cliff and Vermilion Cliff sandstones flat-bottomed canons are excavated ; but in the great shale beds broad valleys are opened, and the flood-plains of adjacent streams coalesce to form continuous plains. The broadest plains are as a rule carved from the thickest beds of shale, and these are found at the top of the Jura-Trias and near the base of the Cre- taceous. Where the streams from the mountains cross the Blue Gate, the Tununk, or the Flaming Gorge shale at a favorable angle, a plain is the result. The plain which lies at the southern and western bases of Mount Hil- lers is carved chiefly from the Tununk shale (see Figure 27). The plain sloping eastward from Mount Pennell (Figure 36) is carved from the Blue Gate and Tununk shales. The Lewis Creek plain, which lies at the west- ern base of Mount Ellen, is formed from the Blue Gate, Tununk, and Masuk shales, and the planation which produced it has so perfectly truncated the Tununk and Blue Gate sandstones that their outcrops cannot be traced (Figures 61, 39, and 42). The plain which truncates the Crescent arch (Figure 49) is carved in chief part from the Flaming Gorge shale. Toward the east it is limited by the outcrops of the Henry's Fork conglomerate, but toward the mountain it cuts across the edge of the same conglomerate and extends over Tununk shale to the margin of the trachyte. Fig. 61.— Cross-section of the Lewis Creek Plain. M, Masuk Shale. BG, Blue-Gate Group. T, Tununk Group. HF, Henry's Fork conglomerate. Scale, 1 inch = 4,000 feet. SHIFTING OF WATERWAYS. 120 The streams which made these plains and which maintain them, accom- plish their work by a continual shifting of their channels ; and where the plains are best developed they employ another method of shifting — a method which in its proper logical order must be treated in the discussion of allu- vial cones, but which is practically combined in the Henry Mountains with the method of planation. The supply of detritus derived from the erosion of the trachyte is not entirely constant. Not only is more carried out in one season than another and in one year than another, bnt the work is accomplished in part by sudden storms which create great floods and as suddenly cease. It results from this irregularity that the chan- nels are sometimes choked by debris, and that by the choking of the chan- nels the streams are turned aside to seek new courses upon the general plain. The abandoned courses remain plainly marked, and one who looks down on them from some commanding eminence can often trace out many stages in the history of the drainage. Where a series of streams emerge from adjacent mountain gorges upon a common plain, their shiftings bring about frequent unions and separations, and produce a variety of combina- tions. Fig. (i2.— Ideal sketch to illustrate the Shifting of waterways on a slope of Planation. 9 II M 130 LAND SCULPTURE. The accompanying sketch, Figure G2, is not from nature, but it serves to illustrate the character of the changes. The streams which issue from the mountain gorges a and b join and flow to z; while that which issues at c flows alone to x. An abandoned channel, n, shows that the stream from b was formerly united with that from c, and flowed to x; and another channel, m, shows that it has at some time maintained an independent course to y. By such shiftings streams are sometimes changed from one drainage system to another ; the hypothetical courses, x, y, and 2, may lead to different riv- ers, and to different oceans. An instance occurs on the western flank of the mountains. One of the principal heads of Pine Alcove Creek rises on the south slope of Mount Ellen and another on the northwest slope of Mount Pennell. The two unite and flow southward to the Colorado River. They do not now cross an area of planation, but at an earlier stage of the degradation they did ; and the portions of that plain which survive, indicate by the direction of their slopes that one or both of the streams may have then discharged its water into Lewis Creek, which runs northward to the Dirty Devil River. As the general degradation of the region progresses the streams and their plains sink lower, and eventually each plain is sunk completely through the shale whose softness made it possible. So soon as the streams reach harder rock their lateral corrasion is checked, and they are no longer free to change their ways. Wherever they chance to run at that time, there they stay and carve for themselves canons. Portions of the deserted plains remain between the canons, and having a durable capping of trachyte gravel are long preserved. Such stranded fragments abound on the slopes of the mountains, and in them one may read many pages of the history of the degradation. They form tabular hills with sloping tops and even pro- files. The top of each hill is covered with a uniform layer of gravel, be- neath which the solid rock is smoothly truncated. The slope of the hill depends on the grade of the ancient stream, and is independent of the hard- ness and dip of the strata. The illustration represents a hill of planation On the north slope of Mount Ellsworth. It is built of the Gray Cliff sandstone and Flaming Gorge shale, inclined at angles varying from 25° to 45°; but notwith- HILLS OF PLANATION. 131 standing" their variety of texture and dip the edges of the strata are evenly cut away, so that their upper surface constitutes a plane. The stream which performed this truncation afterward cut deeper into the strata and carved the lower table which forms the foreground of the sketch. It has now abandoned this plain also and flows through a still deeper channel on the opposite side of the hill. Fig. 63.— A Hill of Planatiou. The phenomena of planation are further illustrated in the region which lies to the northwest of the Henry Mountains. Tantalus and Temple Creeks, rising under the edge of the Aquarius Plateau, transport the trachyte of the plateau across the region of the Waterpocket flexure to the Dirty Devil River. Their flood-plains are not now of great extent, but when their drainage lines ran a few hundred feet higher they appear to have carved into a single plain a broad exposure of the Flaming Gorge shale, which then lay between the Waterpocket and Blue Gate flexures. At the Red Gate where the Dirty Devil River passes from a district of trachyte plateaus to the district of the Great Flexures, it follows for a few 132 LAND SCULPTURE. miles the outcrop of the Shhiarump shale, and the remnants of its aban- doned flood-plains form a series of terraces upon eachbank. Small streams from the sides have cut across the benches and displayed their structure. Each one is carved from the rock in situ, but each is covered by a layer of the rounded river gravel. The whole are results of planation; and they serve to connect the somewhat peculiar features of the mountain slopes with the ordinary terraces of rivers. River terraces as a rule are carved out, and not built up. They are always the vestiges of flood-plains, and flood-plains are usually produced by lateral corrasion. There are instances, especially near the sea-coast, of river-plains which have originated by the silting up of valleys, and have been afterward partially destroyed by the same rivers when some change of Fig. 64. — Ideal cross-section of a Terraced River Valley, after Hitchcock. A, 13, C, D, E, aud F, Allu- vial deposits. G, Indurated rock, in situ. level permitted them to cut their channels deeper ; and these instances, con- spiring with the fact that the surfaces of flood-plains are alluvial, and with the fact that many terraces in glacial regions are carved from unconsoli- dated drift, have led some American geologists into the error of supposing that river terraces in general are the records of sedimentation, when in fact they record the stages of a progressive corrasion. . The ideal section of a terraced river valley which 1 reproduce from Hitchcock (Surface Geology, Plate XII, figure 1) regards each terrace as the remnant of a separate deposit, built up from the bottom of the valley. To illustrate my own idea I have copied his profile (Figure 65) and interpreted its features as the results of lateral corrasion or planation, giving each bench a capping of alluvium, but constituting it otherwise of the preexistent material of the valley. The preexistent material in the region of the Henry Mountains RIVER TERRACES. 133 is always rock in situ, but in the Northern States it often includes glacial drift, modified or unmodified. There is a kindred error, as I conceive, involved in the assumption that the streams which occupied the upper and broader flood-plains of a valley were greater than those which have succeeded them. They may have been, or they may not. In the process of lateral corrasion all the material that is worn from the bank has to be transported by the water, and where the bank is high the work proceeds less rapidly than where it is low. A stream which degrades its immediate valley more rapidly than the surrounding country is degraded (and the streams which abound in terraces are of this character) steadily increases the height of the banks which must be excavated in planation and diminishes the extent of its flood-plain; and Fig. 65. — Ideal cross-section of a Terraced River Valley, regarded as a result of Planation. A, B, C &c, Alluvial deposits. G, Pretixisteut material from which the valley was excavated. this might occur even if the volume of the stream was progressively increasing instead of diminishing. Of the same order also is the mistake, occasionally made of ignor- ing the excavation which a stream has performed, and assuming that when the upper terraces were made the valley was as open as at present, and the volume of flowing water was great enough to fill it. Alluvial Cones. Wherever a stream is engaged in deposition instead of corrasion — wherever it deposits its load — there is a shifting of channel by a third pro- cess. The deposition of sediment takes place upon the bottom of the chan- nel and upon its immediate banks, and this continues until the channel bottom is higher than the adjacent country. The wTall of the channel is 134 LAND SCULrTUltE. then broken through at some point, and the water abandons its old bed for one which is lower. Such occurrences belong to the histories of all river deltas, and the devastation they have wrought at the mouths of large rivers has enforced attention to their phenomena and stimulated a study of their causes. The same thing happens among the mountains. Wherever,, as in Nevada and Western Utah, the valleys are the receptacles of the detritus washed out from the mountains, the foot-slopes of the mountains consist of a series of alluvial cones. From each mountain gorge the products of its erosion are discharged into the valley. The stream which bears the debris builds up the bed of its channel until it is higher than the adjacent land and then abandons it, and by the repetition of this process accumulates a conical hill of detritus which slopes equally in all directions from the mouth of the mountain gorge. At one time or another the water runs over every part of the cone and leaves it by ever}?- part of its base; and it sometimes happens that the opposite slopes of the cone lead to different drainage systems. An illustration may be seen in Red Rock Pass at the north end of Cache Valley, Idaho. Lake Bonneville, the ancient expansion of Great Salt Lake,* here found outlet to the basin of the Columbia, and the chan- nel carved by its water is plainly marked. For a distance of twelve miles the bed of the channel is nearly level, with a width of a thousand feet. Midway, Marsh Creek enters it from the east, and has built an alluvial cone which extends to the opposite bank and divides it into two parts. In the construction of the cone Marsh Creek has flowed alternately to the north and to the south, being in one case a tributary to the Snake and Columbia Rivers and to the Pacific Ocean, and in the other to the Bear River and Great Salt Lake. So far as the creek is known to white men it is a tributary of the Snake, but an irrigating ditch that has been dug upon its cone carries part of its water to the Bear. Another illustration exists at the mouth of the Colorado River. As *Lake Bonneville is described in volume III (Geology) of the "U. S. Geog. Sur- veys West of the 100th Meridian," pp. 88-104; and less fully in the American Natu- ralist for November, 1876, and the American Journal of Science for March, 1876, p. 228. See also Johnson's Cyclopedia, article " Sevier Lake." NATURAL FLOODING OF THE COLORADO DESERT. 135 lias been shown by Blake in the fifth volume of the Pacific Railroad Reports (p. 236), the delta of the Colorado — or in other words the alluvial cone which is built at its mouth — has extended itself completely across the Gulf of California, severing the upper end from the lower and from the ocean, and converting it into a lake. In continuing the upbuilding of the delta the river has flowed alternately into the lower gulf and into its severed segment. At the present day its mouth opens to the lower gulf; but at rare intervals a portion of its water runs by the channel known as "New River" to the opposite side of the delta. While it is abandoned by the river the lake basin is dry, and it is known to human history only as the Colorado Desert. Its bottom, which is lower than the surface of the ocean, is strewn with the remains of the life its waters sustained, and its beaches are patiently awaiting the cycle of change which is slowly but surely pre- paring to restore to them their parent waves. Fig. 66. — Cross-section of inclined strata, to illustrate Monoclinal Shifting of waterways. Monoclinal Shifting. In a fourth manner drainage lines are unstable. In a region of inclined strata there is a tendency on the part of streams which traverse soft beds to continue therein, and there is a tendency to eliminate drainage lines from hard beds. In Figure 66, S represents a homogeneous soft bed, and H and K, homogeneous hard beds. A and B are streams flowing through channels opened in the soft rock, and in the hard. As the general degradation progresses the stream at a abrades both sides of its channel with equal force; but it fails to corrade them at equal rates because of the inequality of the resistance. It results that the chan- nel does not cut its way vertically into the hard rock, but works obliquely downward without changing its relation to the two beds; so that when the degradation has reached the stage indicated by the dotted line, the stream 13G LAND SCULPTURE. // flows at a, having been shifted horizontally by circumstances dependent on the dip and order of the strata. At the same time the stream at B, encountering' homogeneous material, cuts its way vertically downward to b ; and a continuance of the process carries it completely through the hard rock and into the soft. Once in the soft it tends like the other streams to remain there; and in the course of time it finds its way to the lower edge and establishes a channel like that at A. The effect of this process on the course of a stream which runs obliquely across inclined beds is shown in Figure 67. The outcrops of a * s ff series of hard and soft strata, H, H, H and S, S, are repre- v i; sented in ground plan, and the direction of their dip is indicated by the arrow. Supposing that a stream is thrown across them in the direction of the dotted lines and that the land is then degraded, the following changes will take place. The portion of the stream from c to d will sink through the soft rock down to the surface of the hard, and then follow down the slope of the hard, until at last its whole course will be transferred to the line of ofoutcro soTiucifued seParation between the two, and its position (with refer- strata, to illustrate the ence to the outcrops which will then have succeeded the results of Monoclinal . . it rm Shifting. original) will be represented by the line g c. I he por- tion from e to d sinking first through the hard bed and then through the soft, will be deflected in the same manner to the position e h g. The points e and c will retain their original relations to the strata. The same changes will affect the portion from e to /; and the original oblique course will be converted into two sets of courses, of which one will follow the strike of the strata and the other will cross the strike at right angles. The character of these changes is independent of the direction of the current. They are not individually of great amount, and they do not often divert streams from one drainage system to another nor change their general directions. Their chief effects are seen in the details of drainage systems and in the production of topographic forms. The tendency of hard strata to rid themselves of waterways and of soft strata to accumulate WATERPOCKET CANON. 137 them, is a prime element of the process which carves hills from the hard and valleys from the soft. Where hard rocks are crossed by waterways they cannot stand higher than the adjacent parts of the waterways; but where they are not so crossed they become divides, and the "law of divides" conspires with the "law of structure" to carve eminences from them. The tendency of waterways to escape from hard strata and to abide in soft, and their tendency to follow the strike of soft strata and to cross hard at right angles, are tendencies only and do not always prevail. They are opposed by the tendency of drainage lines to stability. If the dip of the strata is small, or if the differences of hardness are slight, or if the changes of texture are gradual instead of abrupt,- monoclinal shifting is greatly reduced. / Waterpocket Canon is one of the most remarkable of monoclinal val- levs ; and it serves to illustrate both the rule of monoclinal shifting- and its exception. The principal bed of soft rock which outcrops along the line of the Waterpocket flexure is the Flaming Gorge shale, having a thickness of more than one thousand feet. Through nearly the whole extent of the out- crop a valley is carved from it, but the valley is not a unit in drainage. At the north it is crossed by the Dirty Devil River and by Temple and Tan- talus Creeks, and the adjacent portions slope toward those streams. At the south it is occupied for thirty miles by a single waterway — the longest monoclinal drainage line with which I am acquainted. The valley here bears the name of Waterpocket Canon, and descends all the way from the Masuk Plateau to the Colorado River. The upper part of the canon is dry except in time of rain, but the lowrer carries a joerpetual stream known as Hoxie Creek. Whatever may have been the original meanderings of the lat- ter they are now restrained, and it is limited to the narrow belt in which the shale outcrops. As the canon is worn deeper the channel steadily shifts its position down the slope of the underlying Gray Cliff sandstone, and carves away the shale. But there is one exceptional point where it has not done this. When the bottom of the canon was a thousand feet higher the creek failed, at a place where the dip of the strata was comparatively small, to shift its channel as it deepened it, and began to cut its way into the 138 LAND SCULPTURE. massive sandstone. Having once entered the hard rock it could not retreat but sank deeper and deeper, carving a narrow gorge through which it still runs making a detour from the main valley. The traveler who follows down Waterpockct Canon now comes to a place where the creek turns from Fig. 68. — Waterpockct Canou and the Horseshoe Beud of Hoxie Creek. the open canon of the shale and enters a dark cleft in the sandstone. He can follow the course of the water (on foot), and will be repaid for the wet- ting of his feet by the strange beauty of the defile. For nearly three miles he will thread his way through a gorge walled in by the smooth, curved faces of the massive sandstone, and so narrow and devious that it is gloomy for lack of sunlight ; and then he will emerge once more into the open canon. Or if he prefer he can keep to his saddle, to the open daylight, and to the out- crop of the shale, and riding over a low divide can reach the mouth of the gorge in half the distance. THE STABILITY OF DIVIDES. The rain drops which fall upon the two sides of a divide flow in oppo- site directions. However near to the dividing line they reach the earth the work of each is apportioned to its own slope. It disintegrates and trans- SHIFTING OF DIVIDES. 139 ports the material of its own drainage slope only. The divide is the line across which no water flows — across which there is no transportation. It receives the minimum of water, for it has only that which falls directly upon it, and every other point receives in addition that which flows from higher points. It is higher than the surfaces which adjoin it, and since less water is applied to its degradation it tends to remain higher. It tends to maintain its position. Opposed to this tendency there are others which lead to THE INSTABILITY OF DIVIDES, and which will now be considered. Ponding, Planation, and Alluviation. Whenever by ponding, a stream or a system of streams which have belonged to one drainage system are diverted so as to join another there is coincidently a change of divides. The general divide between the two systems is shifted from one side to the other of the area which changes its allegiance. The line which was formerly the main divide becomes instead a subordinate divide separating portions of the drainage system which has increased its area ; and on the other hand a line which . had been a subor- dinate divide is promoted to the rank of a main divide. In like manner the shifting of streams from one system of drainage to another by the exten- sion of flood-plains, or by the building of alluvial cones or deltas, involves a simultaneous shifting of the divides which bound the drainage systems. The changes which are produced by these methods are per saltwn. When a pond or lake opens a new outlet and abandons its old one there is a short interregnum during which the drainage is divided between the two outlets, and the watershed separating the drainage systems is double. But in no other sense is the change gradual. The divide occupies no interme- diate positions between its original and its final. And the same may be said of the changes by planation and alluviation. In each case a tract of country is transferred bodily from one river system to another, and in each case the watershed makes a leap. But there are other methods of change, by which dividing lines move sloivly across the land ; and to these we will proceed. MO LAND SCULPTUEE. Monoclinal Shifting. In regions of inclined strata, the same process which gathers the waterways into the outcrops of the softer beds converts the outcrops of the harder into divides. As the degradation progresses the water- ways and divides descend obliquely and retain the same relations to the beds. The waterways continuously select the soft because they resist erosion feebly, and the watersheds as continuously select the hard because they resist erosion strongly. If the inclination of the strata is gentle, each hard bed becomes the cap of a sloping table bounded by a cliff, and the erosion of the cliff is by sapping. The divide is at the brow of the cliff, and as successive fragments of the hard rock break away and roll down the \ ;:Vw:^l': ~- -'i -,■ " ; fohYbR^Jsy&fifa^&jt*-** Fig. G9. — Ideal cross-section of inclined strata, to show the Shifting of Divides in Cliff Erosion. Suc- cessive positions of a divide are indicated at a, i, and c. slope the divide is shifted. The process is illustrated in the Pink Cliffs of Southern Utah. They face to the south, and their escarpment is drained by streams flowing to the Colorado. The table which they limit inclines to the north and bears the head-waters of the Sevier. As the erosion of the cliffs steadily carries them back and restricts the table, the drainage area of the Colorado is increased and that of the "Great Basin", to which the Sevier River is tributary, is diminished. Unequal and Equal Declivities. In homogeneous material, and with equal quantities of water, the rate of erosion of two slopes depends upon their declivities. The steeper is degraded the faster. It is evident that when the two slopes are upon opposite sides of a divide the more rapid wearing of the steeper carries the divide toward the side of the gentler. The action ceases Fia. 70— Cross profile of a had-iand divide ancl the divide becomes stationary only separating slopes of Unequal Declivity. . Two stages of erosion are indicated, to iiius- when the profile of the divide has been trate the horizontal shifting of the divide. ren(jered symmetric. THE WASTE OF CLIFFS. 141 It is to this law that bad-lands owe much of their beauty. They acquire their smooth curves under what I have called the "law of divides", but the symmetry of each ridge and each spur is due to the law of equal declivities. By the law of divides all the slopes upon one side of a ridge are made interde- pendent. By the law of equal declivities a relation is established between the slopes which adjoin the crest on opposite sides, and by this means the slopes of the whole ridge, from base to base, are rendered interdependent. One result of the interdependence of slopes is that a bad-land ridge separating two waterways which have the same level, stands midway between them ; while a ridge separating two waterways which ha^e differ- ent levels, stands nearer to the one winch is higher. It results also that if one of the waterways is corraded more rapidly than the other the divide moves steadily toward the latter, and eventually, if the process continues, reaches it. When this occurs, the stream with the higher valley abandons the lower part of its course and joins its water to that of the lower stream. Thus from the shifting of divides there arises yet another method of the shifting of waterways, a method which it will be con- venient to characterize as that of abstraction. A stream which for any reason is able to corrade its bottom more rapidly than do its neighbors, expauds its valley at their expense, and eventually " abstracts " them. And con- versely, a stream which for any reason is able to corrade its bottom less rapidly than its neighbors, has its valley contracted by their encroachments and is eventually "abstracted" by one or the other. The diverse circumstances which may lead to these results need not be enumerated, but there is one case which is specially noteworthy on account of its relation to the principles of sculpture. Suppose that two streams which run parallel and near to each other corrade the same material and degrade their channels at the same rate. Their divide will run midway. But if in the course of time one of the streams encounters a peculiarly hard mass of rock while the other does not, its rate of corrasion above the ob- struction will be checked. The unobstructed stream will outstrip it, will encroach upon its valley, and will at last abstract it; and the incipient cor- rasion of the hard mass will be stopped. Thus by abstraction as well as by monoclinal shifting, streams are eliminated from hard rocks. 142 LAND SCULPTURE. Resume. — There is a tendency to permanence on the part of drainage lines and divides, and they are not displaced without adequate cause. Hence every change which is known to occur demands and admits of an explanation. (a) There are four ways in which abrupt changes are made. Streams are diverted from one drainage system to another, and the watersheds which separate the systems are rearranged, (1) by ponding, due to the elevation or depression of portions of the land; • (2) by planation, or the extension of flood-plains by lateral corra- sion; (3) by alluviation, or in the process of building alluvial cones and deltas; and (4) by abstraction. {b) There are two ways in which gradual changes are effected : (1) When the rock texture is variable, it modifies and controls by monoclinal shifting the distribution in detail of divides and waterways. (2) When the rock texture is uniform, the positions of divides are adjusted in accordance with the principle of equal declivities. The abrupt changes are of geographic import; the gradual, of topo- graphic. The methods which have been enumerated are not the only ones by which drainage systems are modified, but they are the chief. Very rarely streams are "ponded" and diverted to new courses through the damming of their valleys by glaciers or by volcanic ejecta or by land-slips. More frequently they are obstructed by the growing alluvial cones of stronger streams, but only the* smallest streams will yield their " right of way" for such cause, and the results are insignificant. The rotation of the earth, just as it gives direction to the trade-winds and to ocean currents, tends to deflect rivers. In the southern hemisphere streams are crowded against their left banks and in northern against the right. But this influence is exceedingly small. Mr. Ferrel's investigations ANTECEDENT DRAINAGE. 143 show that in latitude 45° and for a current velocity of ten miles an hour, it is measured by less than one twenty-thousandth part of the weight of the water (American Journal of Science, January, 1861). If its effects are ever appreciable it must be where lateral corrasion is rapid; and even there it is probable that the chief result is an inclination of the flood-plain toward one bank or the other, amounting at most to two or three minutes. CONSEQUENT AND INCONSEQUENT DRAINAGE. If a series of sediments accumulated in an ocean or lake be subjected to a system of displacements while still under water, and then be converted to dry land by elevation en masse or by the retirement of the water, the rains which fall on them will inaugurate a drainage system perfectly con- formable with the system of displacements. Streams will rise along the crest of each anticlinal, will flow from it in the direction of the steepest dip, will unite in the synclinals, and will follow them lengthwise. The axis of each synclinal will be marked by a watercourse; the axis of each anticlinal by a watershed. Such a system is said to be consequent on the structure. If however a rock series is affected by a system of displacements after the series has become continental, it will have already acquired a system of waterways, and provided the displacements are produced slowly the waters will not be diverted from their accustomed ways. The effect of local elevation will be to stimulate local corrasion, and each river that crosses a line of up- lift will inch by inch as the land rises deepen its channel and valorously maintain its original course. It will result that the directions of the drain- age lines will be independent of the displacements. Such a drainage sys- tem is said to be antecedent to the structure. But if in the latter case the displacements are produced rapidly the drainage system will be rearranged and will become consequent to the structure. It has frequently happened that displacements formed with mod- erate rapidity have given rise to a drainage system of mixed character in which the courses of the larger streams are antecedent and those of the smaller are consequent. There is a fourth case. Suppose a rock series that has been folded and eroded to be again submerged, and to receive a new accumulation of un- 144 LAND SCULPTUEE. conforming sediments. Suppose further that it once more emerges and that the new sediments are eroded from its surface. Then the drainage system will have been given by the form of the upper surface of the supe- rior strata, but will be independent of the structure of the inferior scries, into which it will descend vertically as the degradation progresses. Such a drainage system is said to be superimposed by sedimentation upon the struct- ure of the older series of strata. Fifth. The drainage of an alluvial cone or of a delta is independent of the structure of the bed-rock beneath; and if in the course of time erosion takes the place of deposition and the alluvial formation is cut through, the drainage system which is acquired by the rocks beneath is not consequent upon their structure but is superimposed by alleviation. Sixth. The drainage of a district of planation is independent of the structure of the rock from which it is carved; and when in the progress of degradation the beds favorable to lateral corrasion are destroyed and the waterways become permanent, their system may be said to be superimposed by planation. In brief, systems of drainage, in their relation to structure, are (A) consequent (a) by emergence, when the displacements are subaqueous, and (b) by sudden displacement; (B) antecedent-, and (C) superimposed (a) by sedimentation, or subaqueous deposition, (b) by alluviation, or subaerial deposition, and (c) by planation. THE DRAINAGE OF THE HENRY MOUNTAINS is consequent on the laccolitic displacements. The uplifting of a laccolite, like the upbuilding of a volcanic cone, is an event of so rapid progress that the corrasion of a stream bed cannot keep pace with it. We do not know that the site of the mountains was dry land at the time of their elevation; but if it was, then whatever streams crossed it were obstructed and turned from their courses. If it was not, there were no preexistent waterways, and SUPERIMPOSED DRAINAGE. 145 the new ones, formed by the first rain which fell upon the domes of strata, radiated from the crests in all directions. The result in either case would be the same, and we cannot determine from the present drainage system whether the domes were lifted from the bed of the Tertiary lake or arose after its subsidence. But while the drainage of the Henry Mountains is consequent as a whole, it is not consequent in all its details, and the character of its partial inconsequence is worthy of examination. Let us begin with the simplest case. The drainage system of Mount Ellsworth is more purely consequent than any other with which I am ac- quainted. In the accompanying chart the point c marks the crest of the Ellsworth dome ; the inner circle represents the line of maximum dip of the "X Fig. 71. — Drainage system of the Ellsworth Arch. arching strata and the outer circle the limit of the disturbance. It will be seen that all the waterways radiate from the crest and follow closely the directions in which the strata incline. At a the Ellsworth arch touches that of Mount Holmes and at b that of Mount Hillers; and the effect of the com- pound inclination is to modify the directions of a few of the waterways. 10 H M 14G LAND SCULPTUKE. Turning now to Mount Holmes, we find that its two domes are not equally respected by the drainage lines. The crest of the Greater arch (see Figure 72) is the center of a radiating system, but the crest of the Lesser Fig. 72. — Drainage system of the Holmes Arches. arch is not; and waterways arising on the Greater traverse the Lesser from side to side. More than this, a waterway after following the margin of the Lesser arch turns toward it and penetrates the flank of the arch for some distance. In a word, the drainage of the Greater arch is consequent on the structure, while the drainage of the Lesser arch is inconsequent. There are at least two ways in which this state of affairs may have arisen. HISTORY OF TOE HOLMES ARCHES. 147 First, the Greater arch may have been lifted so long before the Lesser that its waterways were carved too deeply to be diverted by the gentle flex- ure of the latter. The drainage of the Lesser would in that case be classed as antecedent. If the Lesser arch were first formed and carved, the lift- ing of the Greater might throw a stream across its summit ; but it could not initiate the waterways which skirt the slopes of the Lesser, especially if those slopes were already farrowed by streams which descended them. If the establishment of the drainage system depended on the order of up- lift, the Greater arch is surely the older. Second, the drainage of the Lesser arch may have been imposed upon it by planation at a very late stage of the degradation. Whatever was the origin of the arches, and whatever was the depth of cover which they sus- tained, the Greater is certain to have been a center of drainage from the time of its formation. When it was first lifted it became a drainage center because it was an eminence; and afterward it remained an eminence because it w.as a drainage center. When in the progress of the denudation its dikes were exposed, their hardness checked the wear of the summit and its emi- nence became more pronounced. It was perhaps at about this time that the last of the Cretaceous rocks were removed from the summits and slopes of the two arches and the Flaming Gorge shale was laid bare, and so soon as this occurred the conditions for lateral corrasion were complete. With trachyte in the peaks and shale upon the slopes planation would naturally result, and a drainage system would be arranged about the dikes as a center without regard to the curves of the strata. The subsequent removal of the shale would impart its drainage to the underlying sandstones. Either hypothesis is competent to explain the facts, but the data do not warrant the adoption of one to the exclusion of the other. The waterways of the Lesser arch may be either antecedent, or superimposed by plana- tion. The Greater arch may have been the first to rise or the last. The drainage of Mount Hillers is consequent to the main uplift and to the majority of the minor, but to the Pulpit arch it is inconsequent, In this case there is no question that the arch has been truncated by planation. (Figure 73.) The Hillers dome, rising five times as high as the Pulpit, became the center of drainage for the cluster, and the trachyte-laden 148 LAND SCULPTURE. streams which it sent forth were able to pare away completely the lower arch while it was still unprotected by the hardness of its nucleus. The foot-plain of Mount Hillers, which extends unbroken to the outcrop of the Henry's Fork conglomerate, is continued on several lines across the Pulpit arch, although in the intervals the central area is deeply excavated. The planation stage is just completed, and an epoch of fixed waterways is inaugurated. Fig. 73. — Cross-section of tbe Pulpit Arch, showing its truncation. The drainage of Mount Pennell is consequent in regard to the main uplift, but inconsequent to some of the minor. A stream which rises on the north flank not merely runs across one of the upper series of laccolites, — a companion to the Sentinel, — but has cut into it and divided it nearly to the base. It is probable that the position of the waterway was fixed by plana- tion, but no remnant of the plain was seen. Too little is known of the structure of the central area of Mount Ellen to assert its relation to the drainage. About its base there are five lacco- lites which have lost all or nearly all their cover, and each of these is a local center of drainage, avoided by the streams which head in the mount- ain crest. Four others have been laid bare at. a few points only, and these are each crossed. by one or two streams from higher levels. The remainder are not exposed at all, and their arches are crossed by numerous parallel streams. The Crescent arch is freshly truncated by planation, and the Dana and Maze bear proof that they have at some time been truncated. The laccolites which stand highest with reference to the general surface are exempt from cross-drainage, and the arches which lie low are completely overrun. If we go back in imagination to a time when the erosion of the mount- THE SURVIVAL OF THE HARDEST. 149 jiiii was so little advanced that the stream-beds were three thousand feet higher than they now are, we may suppose that very little trachyte was laid bare. As the surface was degraded and a few laccolites were exposed, it would probably happen that some of the then-existing- streams would be so placed as to run across the trachyte. But being unarmed as yet by the debris of similar material they would corrade it very slowly; and the adjoining streams having only shale to encounter, would so far outstrip them as eventually to divert them by the process of "abstraction". In this way the first-bared laccolites might be freed from cross-drainage and per- mitted to acquire such radiating systems of waterways as we find them to possess. At a later stage when trachyte was exposed at many points and all streams were loaded with its waste, the power to corrade was increased, and the lower-lying laccolites could not turn aside the streams which over- ran them. The work of planation is so frequently seen about the flanks of the Henry Mountains that there seems no violence in referring all the cross- drainage of lateral arches to its action; and if that is done the historv of the erosion of the mountains takes the following form : When the laccolites were intruded, the mounds which they uplifted either rose from the bed of a lake or else turned back all streams which crossed their sites ; and in either case they established upon their flanks a new and " consequent" set of waterways. The highest mounds became centers of drainage, and sent their streams either across or between the lower. All the streams of the disturbed region rose within it and flowed outward. The degradation of the mounds probably began before the uplift was complete, but of this there is no evidence. As it proceeded the convex forms of the mounds were quickly obliterated and concave profiles were substituted. The rocks which were first excavated were not uniform in texture, but they were all sedimentary and were soft as compared to the trachyte. The Tertiary and probably the Upper Cretaceous were removed from the summits before any of the igneous rocks were brought to light, and during their removal the tendency of divides to permanence kept the drainage centers or maxima of surface at substantially the same points. When at length the trachyte was reached its hardness introduced a new 150 LAND SCULPTURE. factor. The eminences which contained it were established more firmly as maxima, and their rate of degradation was checked. With the checking of summit degradation and the addition of trachyte to the transported material, planation began upon the flanks, and by its action the whole drainage has been reformed. One by one the lower laccolites are unearthed, and each one adds to the complexity and to the permanence of the drainage. If the displacements were completed before the erosion began, the mountains were then of greater magnitude than at any later date. Before the igneous nuclei were laid bare and while sedimentary rocks only were subject to erosion, the rate of degradation was more rapid than it has been since the hardness and toughness of the trachyte have opposed* it. If the surrounding plain has been worn away at a uniform rate, the height of the mountains (above the plain) must have first diminished to a minimum and afterward increased. The minimum occurred at the begin- ning of the erosion of the trachyte, and at that time the mountains may even have been reduced to the rank of hills. They owe their present mag- nitude, not to the uplifting of the land in Middle Tertiary time, but to the contrast between the incoherence of the sandstones and shales of the Meso- zoic series and the extreme durabilit}^ of the laccolites which their destruc- tion has laid bare. And if the waste of the plain shall continue at a like uniform rate in the future, it is safe to prophesy that the mountains will for a while continue to increase in relative altitude. The phase which will give the maximum resistance to degradation has been reached in none of the mountains, except perhaps Mount Hillers. In Mount Ellen the lacco- lites of the upper zone only have been denuded ; the greater masses which underlie them will hold their place more stubbornly. The main bodies of Mounts Ellsworth, Holmes, and Pennell are unassailed, and the present prominence of their forms has been accomplished simply by the valor of their skirmish lines of dikes and spurs. In attaching to the least of the peaks the name of my friend Mr. Holmes, I am confident that I commemo- rate his attainments by a monument which will be more conspicuous to future generations and races than it is to the present. CHAPTER VI. ECONOMIC. There is little to add to what has already been said of the economic value of the mountains, and this chapter is hardly more than a regrouping of facts scattered through those that precede. . Coal. — Possibly some valuable though restricted deposit was over- looked ; but it is safe to say that no thick and continuous bed will be found. The Cretaceous sandstones all contain thin and local beds — enough to mark them as coal-bearing rocks — but there are no seams of value. The best outcrop was seen in the bank of the south branch of Lewis Creek where it crosses the upturned edge of the Blue Gate sandstone. The seam has a thickness of four feet only, and is not well disposed for mining. But if the Cretaceous coals were well developed it is to be doubted if they would ever be used. They could have no local market. They could not be carried to the east or south on account of the canons. If taken northward they would have to compete with the coal of Castle Valley, which is more convenient and very abundant. If taken westward to the metal mines of Nevada and Western Utah they would be undersold by the more accessible coals found on the headwaters of the Virgin River and Kanab Creek, and even by those of the Kaiparowits Plateau. The Gypsum and Building Stones of the region need not be described. They are plentiful in many parts of Utah, and however abundant in this remote place can never be in demand. Gold, Silver, etc. — Three parties of " prospectors " have at different times made unsuccessful search for metalliferous veins. In the course of my survey I spent more than a month's time among the crystalline and meta- morphic formations of the mountain tops, and although directing my atten- tion constantly to the rocks, did not discover a fissure vein. Combining these negative data with certain theoretic considerations which are set forth in the fourth chapter, I am led to the very confident opinion that the essential conditions for the production of fissure veins have not existed in 151 152 ECONOMIC. the Henry Mountains, and hence that there are no valuable deposits of the precious metals. The same theoretic considerations apply to other mount- ains of the same character, and I venture to predict that gold and silver will not be found in paying quantity in Navajo Mountain, the Sierra la Sal, the Sierra Abajo, the Sierra Carisso, or the Sierra La Lata. Agricultural Land. — Bowl Creek, both branches of Lewis Creek, and the south branch of Trachyte Creek can readily be led to tracts of land suf- ficiently level for farming, and each furnishes enough water to irrigate sev- eral hundred acres. It is possible that these tracts will prove useful for farming, but they lie a little too high to be assured of a favorable climate. The lowest has an altitude of 6,000, and the highest of 6,800 feet. Grazing Land. — Above the altitude of 7,500 feet there are many tracts of good grass, available for grazing through the greater part of the year but covered by snow in the winter. Below that level there is a greater area of inferior grass, available through the whole year. By using one portion in summer and the other in winter the mountains could be made to give permanent support to a herd of 3,000 or 4,000 cattle. With such overstocking as is often practiced in Utah they may subsist 10,000 animals for one or two years. Timber. — The trees worthy to be classed as timber are of three species — fir {Abies LJngclmanni), Douglass spruce (A. Louglasii), and yellow pine (Finns ponderosa). The pine is the most valuable and the fir the most abundant. The fir grows upon the mountain slopes, above the level of 7,500 feet and forms thick-set forests. The total area which it covers is not far from twenty-five square miles. The spruce mingles with the fir at the lower edges of the forests ; and the pine forms' a few open groves a little lower down the slopes. It is to be doubted if the trees will ever be cut. Other timber of the same quality and superior in quantity lies between it and the settlements, and neither railroad nor mine nor town is likely to create a local demand. Coal, building stone, gypsum, and timber have no value for lack of a market, either present or prospective ; gold and silver are not found ; and there is little or no land that can be successfully farmed: Only for grazing have the mountains a money value. INDEX. Pago. Abnjo Mountains 67,69, 152 Agricultural lands 152 Alluvial cones aud alluviation 133, 139 Alpine sculpture 3(5, 38 Altitudes of peaks and passes 3, 117 Analogues of the laccolite 98 Ancient rivers no larger than modern 133 Antecedent drainage 143 Arch, Bowl Creek 45 , Crescent 44 , Dana 43 ,G 43 , Maze 44 , Pulpit 33,147 Arches, Forces which produced laccolitic 87 Aridity favorable to geological examination 2,98 of the Colorado Basin in former times 120 Aubrey Sandstone 8 Bad-lauds, Sculpture of 120,140 Bisebof, on contraction of igneous i\ cks in cooling 76 Blue Gate flexure 13 Sandstone 4 Shale 4 Bonneville, Outlet of Lake 134 Bowl Creek arch 45 Canons of the Colorado as obstructions to travel . 1, 151 as evidence of arid climate 120 Carboniferous strata 8 Carriso Mountains 69, 152 Circle Cliffs 14 Cleavage, Slaty, not found 66 , Vertical, produced by sapping 55 Cliffs, Circle ." 14 Climate, Arid, favorable to geological examination 2,98 .Geueral influence of, on erosion .. 103 , Influence of, on sculpture 117 Coal 5,151 Colorado Basin, History of the 84 Desert 134 River, Origin of the 65 Colors of sandstones, Local variation of 7 Comminution of detritus aids transportation 106 Competence .' 110 Conditions of rock flexure 83 Cones, Alluvial 133 Consequent drainage 143 Contact phenomena 65 Contraction of igneous rocks by cooling _ 75, 80 153 154 INDEX. Pago. Corrasion 100,101 , Relation of, to declivity 112 , to friction of flow 109 , to transportation Ill Cover of the laccolites, Depth of the ..1 86,94 Crescent arch 44 Cotta, Prof. Bernhard von, cited , 75 Cretaceous period, Distnrhance at the close of the 10,85 rock series 4 Cross-lamination, Inclination of 7 Dana arch 43 Declivity, General influence of, upon erosion 102 of'streani heds, relation to corrasion 112 .relation to transportation 108 , Relation of, to quantity of water 113 Declivities, Influence of unequal, on divides 140 Degradation (see Erosion) 99, 115 Delesso on contraction of igneous rocks in cooling 76 Densities of igneous rocks 75 of sedimentary rocks 77 Density a condition of laccolitic intrusion 73, 74 of porphyritic trachyte 77 Denudation (see Erosion) 99, 115 of laccolites 21 Deposition hy running water Ill Diameters of laccolites ... 92 Dike near Mouut Ellsworth 59 Dikes and sheets defined 20 , Flat-topped 28 of Mount Ellsworth 23 of Mount Holmes 28 , Relation of, to strains 96 Dinah Creek Pass 3 Dirty Devil River, Flood-plains of 131 Dist ances, Table of 17 Distribution of laccolites, Horizontal 20,30 .Vertical 21,56 Divides in bad-lands, Rounding of 122 .Instability of 139 , Law of • 116 .Stability of 138 Drainage lines, Instability of 125 .Stability of 124 .Systems of 124,143 Dutton, Capt. C. E., on the intrusive rocks 61 Economic geology 151 Elk Mountains 69 Ellen Mount (see Mount Elleu). Ellsworth Mount (see Mount Ellsworth). Energy of muddy streams 108 streams, how measured 106 Equal action, Principle of 123 Erosion, Conditions which control 102 , Influence of climate upon 103 , Influence of declivity upon 102 INDEX. 155 Pag a. Erosion, Influence of rock texture upou 103 , Influence of vegetation upou 104 of Mount Ellsworth 25 , Principles of 99 . Processes of » 99 Farming lands 152 Faults on Mount Ellsworth 23 Mount Holmes 28 ,Kegion of 12, 15 Fish Lake Valley, Structure of 14 Fissure veins limited in depth ' 82 not found in the Henry Mount ains 83, 151 Flaming Gorge Group 0 Flat- topped dikes 28 Flexure of rocks, Conditions of 83 Flood-plain defined 127 Flow of streams, Friction of 107, 109 Folds, The Great '.'. 10,11,85 Forces which produce laccolitic arches ■. 87 Form of laccolites 55 Frost 104 Friction of flow of streams 107, 109 Geikielaccolite 41 Gold and silver 151 Granite, Eruptive 70 Graves, Mr. Walter H 1 Gray Cliff Group 6 Grazing lands 152 Heights 3,117 Henry, Prof. Joseph 1 Henry Mountains, Altitudes of the 2, 1 17 caused by resistance of trachyte to erosion 25, 35 , Contributions of the, to the principles of erosion 99 .Detailed description of the > 22 , Drainage of the 144 , Economic value of the 152 .Planatiou in the 127,149 .Relation of vegetation to type of sculpture in the 118 .Route of travel to the ■. 14 ; their structure laccolitic t 19, 53 Henry's Folk Group 4 Hillers, Mount (see Mount Killers). Hills of planation .- 130 Historical note 66 History of the Colorado Basin , 84 Holmes, Mount (see Mount Holmes). Holmes, Mr. W. H., on the Elk Mountains 70 La Lata and Carriso Mountains 69 Hopkins on the power of currents 106 Howell laccolite 34 , Mr. Edwin E., Fossils discovered by 5 ; obsei vat ion of the Heury Mountains 66 ; observation of the Navajo Mountain 09 Hydrostatic equilibrium, Law of 72 Igneous mountains of the Plateau Province 67 15(5 INDEX. P:ige. Igneous rocks, Contraction of, by cooling 75, HO Inconsequent drainage 1415 Instability of divides 139 drainage lines 125 Interdependence of drainage slopes 123, 141 Internal structure of laccolites 55 Intrusive rocks of tbe Henry Mountaius 59, 61 Isolation of tbe Henry Mountains 2, 18 Jerry Butte 34 Jukes Butte 46 Jukes, Frof. J. Beete, on prismatic structure 76 J ura-Trias rock series 5 Kaibab structure 11 Laccolite A 32 B 32 C 32 D 35 E 41 F 42 ,Geikie 41 II 46 .Hillers 30 , H istory of tbe 95 .Howell 34 , Jukes 46 , Marvine 42 , Newberry 41 of Mount Ellswortb 27 of Mount Pennell 36 of tbe western base of Mount Ellen : 40 ,Peale 47 , Possible analogues of tbe 98 , Scrope 47 .Sentinel rf 38 .Sboulder 42 .Steward : 32 .The, defiued 19 Laccolites, Age of tbe, discussed 84 , Composite 55 , Den udation of 21 , Depth of cover of 86,94 , Detailed description of 22 , Diameters of 92 ,Form of 55,91 , Holmes : .- 27 , Horizontal, distribution of 10 i ntruded in soft beds < 58 , Limital area of 90, 97 thickness of 91 , Material of 59 not prismatic C5 of tbe Elk Mountains 70 of other regions 97 ; size limited 86 subsequent to the strata which iuclose them , 51 INDEX. 157 Laccolites, Vertical distribution of 21,56,05 Laccolitic mountains of the Plateau Province 67,09 structure characteristic of the Henry Mountains 19, 53 Sierra La Sal, etc 09 conditioned by densities 74 correlated with acidic lavas 71 , Discussion of the origin of 72 Lake Bonneville, Outlet of 134 , Great Salt, Outlet of 134 Winipeg, Origin of 126 Laud, Agricultural 152 , Grazing 152 sculpture, Principles of 99, 115 , Timber 152 La Lata Mountains 08, 09, 152 La Sal Mountains 08,09,152 Law of divides 110 , Exception to the 122 Lewis Creek plain 128 Limital area of laccolites 90,97 thickness of laccolites 91 Load, Relation of, to comminution 107 Mallet, Robert, C. E., on contraction of igneous rocks in cooling 70 Marvine laccolite 42 Ma-suk' Plateau 13 Sandstone 4 Shale 4 Maze arch 44 Metamorphism iu the Henry Mountains 65 on Mount Ellen 38 Ellsworth „. 24 Hillers 31 Holmes 28 Minerals of the Henry Mountains 01,04 Mouoclinal shifting 135, 140 Mount Ellen, Character of sculpture of 118 , Drainage of 148 , Structure of 38 , Topography of 3 .Vegetation of 118 Ellsworth, Character of sculpture of 25, 118 , Drainage of 145 , Stereogram of 23,95 , Structure of 22 , Topography of 3 , Vegetation of 118 Hillers, Character of sculpture of 119 , Drainage of 147 , Structure of 30 , Topography of 3 , Vegetation of 118 Holmes, Character of sculpture of 118 , Drainage of 140 , Structure of 27 , Topography of 3 158 INDEX Pago. Mount Holmes, Vegetation of liw Pennell, Character of sculpture of 119 , Drainage of 148 , Structure of 35 , Topography of 3 , Vegetation of . 118 Mount Taylor 71* Mud-cracks, Fossil 9 Navajo Mountain r 69, 152 Newberry, Dr. J. S., on the Sierra Abajo 67 La Sal 68 laccolite 41 Oblique lamination, Inclination of 7 Peale, Dr. A. C, on igneous mountains of Colorado 69 on the Elk Mouutains 70 Peale laccolite 47 Pennell, Mount (see Mount Pennell). Pennelleu Pass 3 Pine Alcove Creek, Former courso of 130 Plauation 126,139 , Hills of 130 Plasticity of solids 82,83,97 Plateaus enumerated 13 Precipitation from running water Ill Pressure a condition for rock flexure 81,83,96 Prismatic structure, Absence of 55,76 defined 55 Ponding 125,139 Porphyritic trachyte 60,64 Porphyry; use of term discussed 63 Powell, Prof. J. W., on the climate of the Colorado Basin 120 Pulpit arch ' 33,147 Rankine on flexure of beams 90 Red Gate flexure 13 , Flood-plains of 131 ,The 16 Revet-crags defined 25 of Mount Hillers 31 of Mount Holmes 29 of Mount Pennell 37 Ripple marks, Fossil 16 River terraces produced by plauation 132 Ri vers, Ancient, no greater than modern 133 Rock texture, Influence of, on sculpture 115, 135, 140 , General influence of, on erosion 103 Rocks of the Henry Mountains, Intrusive C9, 61 , Sedimentary 3 Rotation of t he earth 142 Route to the Henry Mountains 14 San Rafael fold 16,18 Scrope laccolite 47 Sculpture, Alpine 36,38 influenced by climate 117 distribution of divides 116 rock structure 115,135, 140 INDEX. 159 Pago. Sculpture of bad-lands 120 of Mount Ellsworth 25 .Principles of 99,115 Sentinel Butte 38 Sheets and dikes defined 20 of Mount Ellsworth 24 of Mount Holmes 28 , Relation of, to strains 96 Sbin-ar'-ump Group . 6 Shoulder laccolite 42 Sierra Abajo 67,69,152 Carriso -09, 152 La Lata 68,69,152 La Sal 68,69,152 Solidity of rocks not absolute 82,83,97 Specific gravities (see Densities). Specimens of Henry Mountain trachyte 60 Springs; relation to soft strata explained 82 Stability of divides 138 of drainage lines 124 Stereogram, how made 11, 49 of Mount Ellsworth 23,95 of the Henry Mountains 49 and Waterpocket flexure... 11 Steward laccolite 32 ,Mr. John F., cited 66 Strains shown by dikes and sheets 96 Stretching of strata 80 Structure, Law of 115 Sun-cracks, Fossil y Superimposed drainage 144 S.vstems of drainage , 124, 143 Table of altitudes 117 densities of sedimentary rocks 78 in order of superposition 79 trachytes 77 diameters of laccolites... 92 distances 17 mean densities of certain rock series 80 Tantalus Creek 17 .Flood-plains of 131 Taylor, Mount 71 Temple Creek _ 16 , Flood-plains of 131 Terraces, River, produced by planation * 132 Tertiary strata protected by lava 12 Thicknesses of individual strata - 7 Thompson, Prof. A. H 1,66 Thousand Lake Mountain, View from 15 Timber land 152 Trachyte, Porphyritic 60,64 Trachytes of the Henry Mountains not vesicular 51,64 Transportation 100, 101 by streams, analyzed 106 Conditions which determine rate of 110 160 INDEX. Page. Transportation favored by comminution of material 10G declivity 108 quantity of water 109 , Relation of, to corrasion Ill Trend, Absence of 2,30,98 Tu-nunk' Sandstone 4 Shale 4 Unconformities 8,85 Unconformity at Salina , 14 Vegetation, General influence of, on erosion 104 Veins, Absence i«f fissure . . 83, 151 , Fissure, limited in depth .- , 82 Vermilion Cliff Group 6 Vertical cleavage by sapping 55 Volcanoes of the Plateau Province, Extinct 67, 70 Volume of streams, Influence of, on erosiou 104 transportation 109 , Relation of, to declivity 113 Warren, General G. K., on the valley of the Minnesota River 126 Waterpocket Canon 137 flexure, described . 12 , Passes across the 16 Watersbeds (see Divides). Weathering 100 White, Dr. C. A. ; identification of Henry's Fork Group 4 Whitney, Prof. J. D., on inclination of bedding 52 Wiuipeg, Origin of Lake 126 Zones of laccolites , 57, 58, 74 O* Plat'. / r\ v 1 MtfLAKE Mt' v- i * j Li! > IS* >^ y> M > &t / m ; >z .£#" ^ C *f 4- Y ~.-~s y J Wi ♦ ; '<& % *m / X? ,s L ■) - •m^ J. )Ss <- " #» r?*Sp# y . ^/J 3 V ^ s. * /.•> ■ o > * PI -A O ^ STEREOGRAM of the Henry Mountains AND WATERPOCKET FOLD. Including the same area as Plate I. < 9 c f A Scale of Miles. 10 V 15 c f\ 7 \ ■* mc -4 0 M ro * >« MAP of the PlateHI '■ WIf?* WWW & * Henry Mountains, ■ • m . byG.KGilbert - — -— ». Photographed from a model in relief. Scale of Miles. T r. Jk* -M -Jus*-. . \J m A^ffs^irvK 4 ^'Ti^ .-.: .•- ■7T MB t ^Ji >** ,/ V 7$ ^&4 ^ 1 > a Pa ,6 ' J ■sT* ' ybfp r ■ w A e j ' J VJ ?7^ ,.fe:^ W cd /^&$& ■'-" :'0 "^1 Plat* ° LA * ■ r\ y MAP of the ¥ Henry Mo vn tains — byG.KGHbert From a model in relief. - BRIGHAM YOUNG UNIVERSITY 3 1197 21002 6222 'A iv^r* k^ I MPT Vf Ltt Date Due All library items are subject to recall at any time. Ml Om 5 FEB 2 6 20 6 OCT 1 9 *M n w «£S WSS Brigham Young University (V AM