1 f } ‘ \ "et i i fh Me Ay ui i: ' va tae Werte sh ty a a ive i f) \ 4: Cyt Ryd wil Ya\p ¥ i ay ie | i A if N " ag =. ANP yey a eau r Sh It eR ee i ay gen PRONOUN. 42>. cy ial WA ny Britis GROLNGICAL. Seni Be es a war: i PW me AD ea egy M4 ear an) WA 84. Si palin " Lf Nwe | / Heat Ma ay ae Ur th ah A Ay Sain ici en py ) Ay a," 4 * # a i i} on i a od : wT i. e - i = * ot f >, : w » } \' ih: f ¥ iL a > . —e “ a ao SS a = it ~ a - ad ~ as a aiee Cian i 4 ’ 7s ae 4 a > - DEPARTMENT OF THE INTERIOR MONOGRAPHS OF THE UNITED STATES GEOLOGICAL SURVEY rt VOLUME XI WASHINGTON GOVERNMENT PRINTING OFFICE 1885 yr S 4 4 5 s — i Be on 7 - i Py UNITED STATES GEOLOGICAL SURVEY J. W. POWELL DIRECTOR GEOLOGICAL HISTORY OF eh a reo NTA N A QUATERNARY LAKE OF NORTHWESTERN SE YAbb Se >> ; C FEB 7 1887 <2 << BY avg ISRAEL COOK RUSSELL WASHINGTON GOVERNMENT PRINTING OFFICE 1885 1 , yt oF eb SS oe bona" tO See: hee ie 2, Wasuineton, D. C, March 28, 1885. Srr: I have the honor to submit for publication a memoir on Lake Lahontan by Mr. I. C. Russell. The principal work of my Division has been the investigation of the Quaternary lakes of the Great Basin. In this investigation Mr. Russell has been my principal assistant since the year 1880. During the first season he accompanied me in the field for the purpose of familiarizing himself with the methods of research which had been developed in the course of the earlier work, but in subsequent years he was assigned independent districts. His report on the most important of these is communicated in the pres- ent volume. After the completion of his field work, I visited some of the more in- structive localities of the Lahontan basin and repeated his observations. I am thus familiar not only with his methods but with some of the principal facts which he discusses, and am enabled from personal knowledge to char- acterize his work as accurate and thorough. Very respectfully, your obedient servant, . G@ K) GILBERT. Geologist in Charge, Division of the Great Basin. Hon. J. W. Powe tt, Director U. S. Geological Survey. A a ‘ win j fi hits 72 , ‘ Ae ae - rT) ae 7 ‘ ti «,) , ak te un ' ‘ : 4 . ot | > rr 4 ‘ 4 . & 7 » PREFACE. The explorations reported in the present volume are a continuation of the studies of the Quaternary geology of the Great Basin begun by Mr. G. K. Gilbert when the present survey was organized. ‘The work has been carried out under Mr. Gilbert’s direction, and to him I am indebted not only for every facility he could offer for advancing my work, but also for im- portant advice and numerous suggestions. Whatever value may be at- tached to the results of my labors will be due in great measure to the wisdom and unvarying kindness of the Chief of the Division of the Great Basin. With the exception of the reconnaissance of 1881, I have had the assistance of Mr. Willard D. Johnson in all matters relating to topography throughout both the field and office work connected with the preparation of this volume. The energy and completeness with which he has carried for- ward his special work under peculiar difficulties, not met with outside the desert regions of the Far West, deserve the highest praise The accuracy of the accompanying maps that Mr. Johnson has drawn from his own sur- vey will make them a reliable basis for determining future changes in the lakes and rivers of the region explored. During the summer of 1882, I was accompanied by Messrs. W J Me- Gee and George M. Wright, as geological aids, and to each I have the pleasure of crediting much valuable assistance. The accompanying draw- ings of geological sections will attest the accuracy of Mr. McGee’s work. The survey of nearly 8,500 square miles in northern Nevada, which was necessary in order to compile the accompanying pocket map and many of the smaller illustrations, was carried out by Mr. A. L. Webster, assisted Vil Vill PREFACE. by Mr. Eugene Ricksecker. It is to be hoped that Mr. Webster’s work will be issued as an independent atlas sheet, in order that. its full value may be appreciated. Since this report was written the analyses by Prof. F. W. Clarke and Dr. T. M. Chatard, contained in the following pages, have been published in Bulletin No. 9 of this Survey, to which the reader is referred for additional information in reference to methods of analysis. r-C, BR. CLOENa ivi NE Ss ERO RO Re RAN SME EAT ate ee metse ee estes aes eeste eae sean ans citer © secede vews\eeeaelscncsices= =e EP REDA ORE eae Sees e ieeesee neo ele en seen a aainncccisewcsissccicccsec coUscssemmaciscccee AND SINRAGH Gis WOR OCP NDE heb Scc ce Sootio se cebeocoe O60CEd ONES cabo LEE eeoboooscne cEcbooLese CHAPTER I.—INTRODUCTORY. (NPG TEM Oe Rnb y Ssnese sec ese Sees ce seeneoaaee cencng Cao gs0 nnacoo cOaSeensboss CoenenEconce Ling Geraeit E .0 2 2 cod Seccesase -eSses ROSE Sooners Soaceeococs6 Sedehe cencases Csncce cooanees I MNATIONS .occcoseecos cooste s0Gs0s Soobss Sanene Coo RSUGUOC US FCO600 COEnoS OSEEreaceHeseecoe UHAPTER II.—GENESIS OF LAKE LAHONTAN. The formation of lacustral basins..........-...----..---- SpSCtRSe coaSos sSSceeEsocoooneO cane Oni cinto fiber ia bOntans DAS telat tole iaiee mnet= eae nee eelnee cee ese sees ae= eons ~saeisee Georrapnicaliextentwotmoake manontanlcca-sstsemss) joe coec does. ceocice eaecccsseecccs comes < sibeyiny amp eran Ch ASW se ese Ns oracles Sam neil aaa <= moO DOA BCOSSN ocoSesasoees ANG TRIG) SPS oo = S50 otidnes 065 Boca BE OE OS DOS EE ERO HOO BBE SE> SEOBED BSCE Se SESaSeaeeccse QNHON OP OU Bocas saasobea shee 2SoSe NC SSSSS HOE eS BOSSES SR ERE OE Sr ROD CEE CO BOLE pb ecooboos CHAPTER II].—PHYSIOGRAPHY OF THE LAHONTAN BASIN. \WEMIBGS cose scosoe copies Soe don Sosa soos dda sesescooecsgsced 6555 Wao) seiaetie nates cones MWIGUINISHe ostoRectae 6 sO TSH OS RODE OO BOSD ES SOC DRS nO bs OEE ABE E EE Gene eco COD OS See pDeros WRAV GPS) aso sae ane ws afin = eee as aae ees ayaa wi eee Terraces‘and séa-elitffs)s_ 2. Ustcecee eas ae atone ars ee a See Sie Oe ee ee Baretand embankments: -2 ceeser 236 CHAPTERS. — Link HISTORY OM WAKE, WAHONPAN So ob ooo 2-)< sec do< sae ec ccee ses oes cence em 238 SS USAT ph eee ea eS RL ee as atime Sata a ayeisede See lesa ee siateee o- 249 CHAPTER VII.—Risumi OF HISTORY OF LAKE LAHONTAN ......-------------- -2ee-ee-s-------- 200 (CECA TE AVE L == Gh UPAR RUN AED CED MAUD) ree ey Tae tee smietioo . Seren eelcains ale cle Slescisae Ga wales 254 CHAPTER TX:—GEOLOGICAL AGE OF LAKE LAHONTAN ...--. ------.2-<2- s22-n0 eccces enn ane == 20 269 CHAPTER X.—POsT-LAHONTAN OROGRAPHIC MOVEMENT ...--..--------- ..--------------------- 274 UR IBIOES coos cactess cbceca tend ca dsSelnsag See SSURneHociccic Sap abconn SsaetoSaadboC0 DEEEOIOseCEs Cob seep 285 aT a Pl 1 F TOA GN TABLES OF CHEMICAL ANALYSES. Table A.—Analyses of Ainerican river waters-..-..-.--- 174 B.—Analyses of American spring waters 176 C.—Analyses of the waters of inclosed lakes. - - - 1r0 D.—Composition of the principal lakes and rivers of the ‘paren basin 225 + ee ” es = he A . S rs . 7 Le a = = Ud owe ‘G, | 0g Cee ( —— j Sate dita ee i: ae bal bs I ' : Pi ri a. pa Te ot fi = = * ine ey 1 ‘ a oe cece cr a) te oar? hee F - Suan cee "Ke ; ‘ Fi ~ 7 — a « a? € a =. . a _n : Toran ky, : sae BON ERE ce -* Ft . <= as sk? Op ro b - : i 3 b a ea — cn . 7 a See = Pa iNew eee @ =a 7 » o wr 4 ~ 7 6 am Se SS gh eee : — a ah ee : = ‘. : psf ad ‘ pet P+ ite Catel, eee ea ss ; ' ‘3 : > mile > coveted Pate a! a 1 Coy cce epg Oat ; r 4 : a » ‘ » a ir Artes ieee 4 CO Bed “ ‘ , | , “’ se “7 ry eos a ee UPD MA , Z . aby PLATE ILLUSTRATIONS. I.—Map of the Great Basin, showing position of Lake Lahontan II.— Map of routes of travel and areas surveyed 1V.—Map of the water surface and drainage area of Lake L VII.—Map of the Carson Desert, Nevada IX.—Map of Pyramid and Winnemueca lakes, Nevada X.—Map of Anaho Island, Pyramid Lake, Nevada XI.—Sketch of Pyramid Island, Pyramid Lake, Nevada (from a photograph) XM.—Sketch of the Needles, Pyramid Lake, Nevada (from a photograph) XIT.—Sketch among the Needles (/rom a photograph) XIV.—Sketeh of Musbroom rock, Anaho Island XV.—Map of Walker Lake, Nevada XX.—Map of gravel embankments at Buffalo Springs, Nevada XXI.—Map of gravel embankinents three miles south of Buffalo Springs XXI.—Humboldt Canon, near Rye Patch, Nevada (from a photograph) XXII.—Sections of Lahortan sediments in Humboldt Canon, Nevada XXIV.—Sections of Lahontan sediments in Truckee Canon, Nevada Iil.—Map of pre-Quaternary fault-lines of the Lahontan region ahoniane sees -e esse V.—Map showing depth of Lake Lahontan at highest stage VI.—Map showing land classification of the Lahontan region XXV.—Sections of Lahontan sediments near Agency Bridge, Truckee Canon... .-- XXVI.—Section of Lahontan sediments at Agency 3ridge, Trnekee Cation, Neyada.. - XXVUH.—Section of Lahontan sediments, Truckee Canon XXVIII.—Sections of Lahontan sediments in Walker River Canon, Nevada XXIX.—Map of the present drainage areas of the Lahontan basin XXX.—Tufa crag at Allen’s Springs, Nevada (from a photograph) Do) XXXI.—Map of the water surface of Lake Lahontan at the thinolite stage XXXIL—A characteristic specimen of thinolite (from a photograph) XXXITI.—Dlustrations of the strneture of thinolite-............ XXXIV.—Illustrations of the structure of thinolite.......... XXXV.—A characteristic specimen of dendritic tufa (from a photograph 1 J L gray XXXVI.—Dendritic tufa deposited on a cliff (from a photograph) XXXVI.—Dnitative tufa forms (from a photograph)........----.- XXXVIU.—An island of tnfa in Pyramid Lake (from a photograph) XXXIX.—Tufa towers on the shores of Pyramid Lake (from « photograph) XL.-—Tufa castle, west shore of Pyramid Lake, Nevada (Jrom a photograph) XLI.—Tuafa domes in Pyramid Lake (from a photograph) XIV ILLUSTRATIONS. PLATE XLII.—Tuta tower on the shore of Winnemucea Lake (from a photograph) ..-...----- XLIII.—Tufa domes in Mono Lake, California (from a photograph) .-...----.-------.-- XLV :—Map of post-Quatern ary, fects oie oe arm octet a ae ete lal ale al ele ele lle FIG. XLV.—Post-Quaternary fault on the south shore of Humboldt Lake (from a photograph) XLVI.—Map of Lake Lahontan (in pocket at end of volume). 1.—Ideal section illustrating Basin Range structure..>.- 2-2-2. -22- 2 os- ooo ee ee anaes 2.—Ideal section through the Black Rock Desert, Nevada....-...-.-..----.-------------- 3.—Ideal section through the Pahute Range, Nevada ...-...-.--.-..-...---.-------------- 4.—Ideal section through Pyramid and Winnemucca lakes, Nevada ....---..----.---.---- 5.—Ideal section through the Carson River Canon, Nevada.-.-.- sees taeeedcecesewaneeees 6.—Deposits of calcium carbonate from sub-lacustral springs .....--.-.-.----------------- 7.—Map of a portion of the east shore of Pyramid Lake, showing position of measured rocks 8: —Ideal profile of ancutitentaCe nae see e ae eee ate ee eee ate eee 9:—Jdeal profile of a cut and! built) terrace= =~ 2 — Soe oe one mm ee ee 10,—Ideal plat and section illustrating the formation of barrier bars..----.--------------- 11.—Ideal plat illustrating the formation of embankments.----.------.------------------- 12.—Diagram illustrating the relative age of gravel terraces and embankments..----.----- 13:—Ideallisection: of. a high-orader deltas <2 cp = 5 erate aim atm lee leg im ala elate) eal le er 14.—Generalized profile of Lahontan terraces..........--....---------2=------=------ ooee 15.—Profile of lithoid terrace and Lahontan beach .----. --.--.--.---.----- ------=--------- 16.—Profile of gravel embankment at west end of Humboldt Lake, Nevada...-.-----.------ 17.—Section of embankment at west end of Humboldt Lake, Nevada.-..-.....--------.----- 18.—Section of bar on the Niter Buttes, Nevada -.--..----. .----.----2- ------.------------- 19.—Map of gravel embai kinents at south end of Winnemucea Lake. .-.---.--..-.--.------ 20.—Section of gravel embaukments at sonth end of Winnemucca Lake....-----.--------- 21.—Sketch-map of gravel embankments in Churchill Valley, Nevada-.----.-.--..-- ee cae 22.—Sketch-map of gravel embankments at south end of Quinn River Mountain, Nevada --- 23'— VOLCANIC GUSt 2S seuss cus ore tarele Rene semis ee eee toe a tata fee ete eo eee eee 24.—Section of White Terrace, west side of Pyramid Lake, Nevada..-..---...-.------------ 25.—Reverse fault in Tea eter gravels-. BES Seo o seas ee Aa sap oot Sernecos aes Saco 26.—Recent faults in lacustral clays, Wanbolit Valley, Newades Sees saesinigta so sian eoese eae 27.—Section of current-bedded gravel between lithoid and thinolite tufa ----....-.---..--- 28.—Diagram showing succession of tufa deposits ..-....-.--.---------- -.2--. ------.----- 29.—Vertical and horizontal sections of a tufa tower. .-.-..--... -.-..----.-------=--=------ 30.—Section of reservoirs and vats at Eagle salt works, Nevada ...-...----. -------.------- 31.—Curve illustrating the rise and fall of Lake Lahontan........-....-...--------------- 32.—Larval cases of Caddis fly inclosed in tulfai--2- << 5-)- asin =~ oe wee een le 33.—Spear-head of obsidian, from Lahontan sediments .-......--..----.------ -.------------ 34.—Curve of Lahontan climate; Wet versus Dry------.----- ------ s-22 222-00 cone secene - <== 35.—Curve of Lahontan climate; Warm versus Cold ...--- 22-02-22 2 - secre cena eww ene anne —Id: al cross-profiles of fault beds .----....--- ------ --+- -o-0-- eeeeee Sebroso decopcesocls 102 103 107 108 110 120 120 121 122 146 151 164 165 191 204 209 234 237 246 247 261 263 279 LAKE LAHONTAN PL. I Julius Bien & Co. Lith QUATERNARY LAKES. OF THE GREAT BASIN. Quaternary Lakes Boundary of the Great Basin <=" Area represented on Plate XLVI. 0 Scale of Miles. 100 75 50 ci o 100 200 300 ee NS Se GEOLOGICAL HISTORY OF LAKE LAHONTAN, BY ISRAEL C, RUSSELL. ABSTRACT OF MONOGRAPH. The present volume records the history of a large lake which flooded a number of the valleys of northwestern Nevada at a very recent geolog- ical date, but has now passed away. ‘This ancient water-body is known as Lake Lahontan—named in honor of Baron La Hontan, one of the early explorers of the headwaters of the Mississippi—and was the complement of Lake Bonneville. ‘The former, situated mostly within the area now form- ing the State of Nevada, filled a depression along the western border of the Great Basin at the base of the Sierra Nevada; the latter, embraced almost entirely in the present Territory of Utah, occupied a corresponding position on the east side of the Great Basin, at the foot of the Wasatch Mountains. The hydrographic basins of these two water-bodies embraced the entire width of the Great Basin in latitude 41°. Lake Bonneville was 19,750 square miles in area, and had a maximum depth of about 1,000 feet. Lake Lahontan covered 8,422 square miles of surface, and in the deepest part, the present site of Pyramid Lake, was 886 feetin depth. The ancient lake of Utah overflowed northward and cut down its channel of discharge 370 feet. The ancient lake of Nevada did not overflow. Each of these lakes had two high-water stages, separated by a time of desiccation. In the Lahontan Basin, as in the Bonneville, the first great rise was preceded 1 2 GEOLOGICAL HISTORY OF LAKE LAHONTAN. by a long period of desiccation, and was followed by a second dry epoch, during which the valleys of Nevada were even more completely desert than at present. During the second flood stage the lake rose higher than at the time of the first high water, and then evaporated to complete desic- ration. The present lakes of the basin are of comparatively recent date, and are nearly fresh, for the reason that the salts deposited when the Quater- nary lake evaporated were buried or absorbed by the clays and marls that occupy the bottom of the basin. As Lake Lahontan did not overflow, it became the receptacle for all the mineral matter supplied by tributary streams and springs both in sus- pension and in solution. The former was deposited as lacustral sediments and the latter as calcareous tufa, or formed desiccation products when the lake evaporated. The introductory chapter indicates the position of the field of study, and contains a sketch of the Great Basin, as the explorer finds it to-day, of which the desiccated bed of Lake Lahontan forms a part; also a brief notice of previous explorations, and an account of what was known of Lake Lahontan before the present study was begun. Routes of travel and areas surveyed are indicated on Plate II. Chapter II (on the genesis of Lake Lahontan) contains a summary of the faets which show that the lake filled a compound orographic basin, resulting from the tilting of faulted beds. A description is given of the character of the irregular area whose drainage the lake received, together with an account of the outline and area of the basin which held the ancient lake. The question of outlet is discussed in detail, the conclusion being that the lake did not overflow (page 32). Chapter III (on the physiography of the Lahontan Basin) contains a description of the region as it exists at the present time. ‘The most distinct- ive characteristics of the valleys and mountains are briefly noticed; an account of the existing rivers is given, including measurements of volume, chemical composition, etc. The present springs of the basin are also described and analyses of the waters of a few of them presented. These analyses are believed to represent approximately the character of the tribu- ABSTRACT OF MONOGRAPH. 3 taries of Lake Lahontan. The existing lakes are next considered. These are Honey Lake, California; Pyramid, Winnemucca, Humboldt, North Car- son, South Carson, and Walker lakes, Nevada. Each of these is described with some detail with special reference to its geological bearings. All the lakes mentioned: above, excepting Humboldt, are inclosed, %. e., are without outlet, and their waters are somewhat saline and alkaline, but not concentrated brines. They cannot, therefore, be considered as remnants left by the incomplete desiccation of Lake Lahontan. The Soda lakes, near Ragtown, Nevada, are specially considered, and detailed observa- tions are presented which show that they occupy extinct volcanic craters (page 73). Attention is given, on page 81, to the peculiar playas or broad mud-plains of the arid region of the Far West, as well as to the temporary lakes, called playa-lakes, which frequently flood them. Chapter IV (on the physical history of Lake Lahontan) is divided into sections. Section 1 contains a compendious discussion of shore phenomena in general. Section 2 is devoted to the presentation of the shore phenomena of Lake Lahontan, and contains detailed descriptions and maps of the terraces, bars, embankments, etc., that were formed about its shores. The highest of the ancient water lines is named the ‘‘Lahontan Beach.” It indicates the maximum extent of the lake as shown on the accompanying pocket map. The most conspicuous terraces below the Lahontan Beach are the ‘“Lithoid”, “Dendritic”, and “Thinolitic.” Each of these marks the upper limit of a variety of tufa from which it derives its name (page 102). Section 3 treats of the sediments of the lake and presents detailed sec- tions of the exposures observed. The sediments consist of two deposits of lacustral marls, separated by a heavy layer of current-bedded gravels; thus recording two lake periods and an intermediate low-water stage (page 43). Accumulations of pumiceous dust, white marl, and aeolian sands are described under the head of Exceptional Sedimentary Deposits (page 146). Section 5 is devoted to the illustration of geological structure, as dis-_ played in the lake basin, and is followed by a résumé of the physical history of the lake (page 169). 4 GEOLOGICAL HISTORY OF LAKE LAHONTAN. Chapter V (on the chemical history of Lake Lahontan) is also divided into sections. Section 1 treats of.the general chemistry of natural waters as they occur in streams, springs, lakes, oceans, and inclosed lakes or seas, and is an introduction to the chemical history of Lake Lahontan. Section 2 is an account of the tufas precipitated from the water of the lake. These present three main divisions, named, respectively, ‘Lithoid,” “'Thinolitic,” and ‘‘ Dendritic.” The first is a compact, stony variety, and is the oldest of the principal calcareous deposits that sheath the interior of the basin. It occurs from a horizon thirty feet below the Lahontan beach all the way down the sides of the basin to the lowest point now exposed to view (page 190). Thinolite is composed of crystals, and was formed in the ancient lake when it was greatly reduced by evaporation; its upper limit is about 400 feet below the Lahontan beach (page 192). Dendritic tufa has a branch- ing or dendritic structure, whence its name; it is superimposed upon the previously-formed varieties. Its upper limit is 180 feet below the Lahontan beach (page 201). The aggregate thickness of the tufa deposits is from thirty to perhaps fifty or seventy-five feet. Chemical analyses show that all the varieties are composed of somewhat impure calcium carbonate. — Fol- lowing the description of these deposits is a discussion of the conditions favoring the deposition of calcareous tufa from lake waters (page 210). Section 3 considers the salts precipitated from the waters of the lake when evaporation took place, and discusses the manner in which lakes may be freshened by desiccation (page 223). Section 4 contains an account of the efflorescences now forming on the surface of the deserts in the Lahontan Basin, and presents a brief descrip- tion of the more valuable salt-works of the region, which are all supplied by the salts contained in Lahontan sediments (page 230). Chapter VI presents the life history of the ancient lake as determined from the abundant molluscan remains and other fossils that have been found. The shells show that the lake was fresh throughout its higher stages. During the period when thinolite was formed it seems to have been too concentrated to admit of the existence of mollusean life, as no fossils have beén found in that deposit. A chipped implement discovered in the upper lacustral beds ABSTRACT OF MONOGRAPH. 5 indicates that man inhabited the Far West during the last rise of Lake Lahontan (page 247). Chapter VII is a summary of the history of the former lake (page 250). Chapter VIIT contains a discussion of the Quaternary climate as de- termined from the records of Lake Lahontan. The periods of greatest lake expansion are correlated with the two glacial epochs of the Sierra Nevada, and are believed to indicate cold and moderately humid periods (page 259). That the lake did not overflow is taken as evidence that the climate, even during the high stages of the lake, was only moderately humid. The climatic changes that brought about such marked alterations in the character of the Great Basin are thought to have been of moderate intensity, Chapter IX is devoted to a summary of the evidence bearing on the determination of the geological age of the lake. The conclusion reached is that it existed during the Quaternary, but was more recent than the date usually assigned for the close of the glacial epoch. Chapter X brings the present study to a close, and contains an account of the orographic movements that have affected the Lahontan basin since the last high-water period. The post-Lahontan faults actually observed are represented on Plate XLV. CHAPTER: INTRODUCTORY. THE FIELD OF STUDY. The region treated of in the present volume embraces about 90,000 square miles in northwestern Nevada, together with small portions of south- ern Oregon and eastern California. The object of the explorations herewith reported was the study of the Quaternary geology of the country visited, and particularly the geological history of Lake Lahontan—a lake, now extinct, which occupied many of the valleys of northwestern Nevada at a very recent geological date. The basin of Lake Lahontan is one of the many independent drainage areas of which the Great Basin is composed, and its geology is a page in the his- tory of the vast region lying between the Rocky Mountains and the Sierra Nevada. The Great Basin is to-day an arid region, but during the Quaternary its climate was probably colder and more humid than at present. The Sierra Nevada and Wasatch ranges, now for the most part bare of snow during the summer, were formerly crowned with vast névés from beneath which flowed many magnificent ice-rivers; the desert ranges of Utah and Nevada were also snow-covered, and some of them gave birth to local gla- ciers. The valleys which are now dry and treeless, and in many instances absolute deserts, destitute of any kind of vegetation over hundreds of square miles, were then occupied by lakes, the largest of which were comparable in extent and depth with those now drained by the Saint Lawrence Some of these old lakes had outlets to the sea and were the sources of considera- 6 SCENIC FEATURES OF THE FAR WEST. 7 ble rivers, others discharged into sister lakes; a considerable number, how- ever, did not rise high enough to find outlet, but were entirely inclosed, as is the case with the Dead Sea, the Caspian, and many of the lakes of the Far West at the present time. The largest of the Quaternary lakes of the Great Basin, thus far explored, has been very fully described by Mr. Gil- bert and others under the name of Lake Bonneville. The second in size, Lake Lahontan, is the subject of the present report. The topography of the region to which we wish to direct attention, together with its Quaternary hydrography, is represented on the accompa- nying pocket map. ‘The relation of the region to the entire area of interior drainage, and the more general geography of the Far West, is indicated on the frontispiece. Before presenting the results of our geological observa- tions it seems desirable to glance briefly at some of the more prominent characteristics of the region of interior drainage of which the district to be described is a component part. THE GREAT BASIN. In crossing from the Atlantic to the Pacific, between the Mexican boundary and the central portion of Oregon, one finds a region, bounded by the Sierra Nevada on the west and the Rocky Mountain system on the east, that stands in marked contrast in nearly all its scenic features with the remaining portions of the United States. The traveler in this region is no longer surrounded by the open, grassy parks and _heavily-timbered mountains of the Pacific slope, or by the rounded and flowing outlines of the forest-crowned Appalachians, and the scenery suggests naught of the boundless plains east of the Rocky Mountains or of the rich savannas of the Gulf States. He must compare it rather to the parched and desert areas of Arabia and the shores of the Dead Sea and the Caspian. Yo the geographer the most striking characteristic of the country stretching eastward from the base of the Sierra Nevada is that it is a region of interior drainage. For this reason it is known as the “Great Basin.” No streams that rise within it carry their contributions to the 8 GEOLOGICAL HISTORY OF LAKE LAHONTAN. ocean, but all the snow and rain that. falls inside the rim of the basin is returned to the atmosphere, either by direct evaporation from the soil or after finding its way into some of the lakes that occupy the depressions of the irregular surface. The climate is dry in the extreme, the average yearly rainfall probably not exceeding 12 or 15 inches. The area thus isolated from oceanic water systems is 800 miles in length from north to south, and nearly 500 miles broad in the widest part, and contains not far from 208,500 square miles—an area nearly equal to that of France. The southern part of the region includes the Colorado Desert, Death Valley, and much of the arid country in southern California and Ne- vada. In northern Nevada the Carson and Black Rock deserts exhibit the extreme of desolation. The most northerly part of the Great Basin, oceupy- ing the central portion of Oregon, is less barren, its rugged surface abound- ing in long and narrow mountain ranges, volcanic table lands, and isolated mesas, weathering as they grow old into rounded buttes, that are covered with luxuriant bunch-grass and bear a scattered growth of cedars and pines. At the south the valleys of the Great Basin are low-lying, Death Valley and the Colorado Desert being depressed below the level of the sea; but at the north the valleys have a general elevation of from 4,000 to 5,000 feet, while the intervening mountain ranges rise from 5,000 to 7,000 feet above them. Diversifying this region are many mountain ranges and broad desert valleys, together with rivers, lakes, and canons, topographic elements to be found in all quarters of the world, but here characterized by features peculiar to the Great Basin The mountains exhibit a type of structure not described before this region was explored, but now recognized by geologists as the “Basin Range structure.” They are long narrow ridges, usually bearing nearly north and south, steep upon one side, where the broken edges of the composing beds are exposed, but sloping on the other, with a gentle angle,conformable to the dip of the strata. They have been formed by the orographic tilting of blocks that are separated by profound faults, and they do not exhibit the anticlinal and synclinal structures commonly observed in mountains, but are monoclinal instead. DESERTS OF THE GREAT BASIN. S) The valleys or plains separating the mountain ranges, far from being fruitful, shady vales, with life-giving streams, are often absolute deserts, totally destitute of water, and treeless for many days’ journey, the gray- green sagebrush alone giving character to the landscape. Many of them have playas in their lowest depressions—simple mud plains left by the evap- oration of former lakes—that are sometimes of vast extent. In the desert bordering Great Salt Lake on the west and in the Black Rock Desert of northern Nevada are tracts hundreds of square miles in area showing scarcely a trace of vegetation. In winter, portions of these areas are occu- pied by shallow lakes, but during the summer months they become so baked and hardened as scarcely to receive an impression from a horse’s hoof, and so sun-cracked as to resemble tessellated pavements of cream-colored marble. Other portions of the valleys become incrusted to the depth of several inches with alkaline salts which rise to the surface as an efflores- cence and give the appearance of drifting snow. ‘The dry surface material of the deserts is sometimes blown about by the wind, saturating the air with alkaline particles, or is caught up by whirlwinds and carried toa great height, forming hollow columns of dust. These swaying and bending col- umns, often two or three thousand feet high, rising from the plains like pil- lars of smoke, form a characteristic feature of the deserts. Most of the rivers of the Great Basin have their sources in the melting snows of the mountains which form its eastern and western borders, and flow into the desert valleys within the rim of the undrained area. Of such the Bear, Weber, and Sevier rivers are examples along the eastern border ; on the west the Truckee, Carson, and Walker rivers have a similar origin and destiny. A single river, the Humboldt, is anomalous in that both its source and its terminus are well within the area of interior drainage. The rivers of the Great Basin vary greatly in volume with the varying seasons, and some of them disappear entirely during the hot summer months In the streams that are perennial a high percentage of the annual discharge is crowded into a brief space toward the end of the rainy season. Thus the arteries of this parched and heated country make but one feverish pul- sation in a year. The streams usually diminish in volume as they descend into the valleys, and in many instances their waters are lost on the thirsty 10 GEOLOGICAL HISTORY OF LAKE LAHONTAN. deserts and their channels run dry. In general they are larger near their sources than at their mouths. Commonly, too, instead of being pure, spark- ling waters, refreshing to the lips as well as to the eye, they are heavy with sediment and bitter and alkaline to the taste. The lakes into which much of the surface drainage finds its way are commonly saline and alkaline—their shores desert wastes, shunned by animals and by all but salt-loving plants. Of the saline lakes, the typical example is furnished by Great Salt Lake in Utah, an inland sea whose fea- tures call to mind the familiar descriptions of the Dead Sea in Palestine. Mono Lake in California, and Abert and Summer lakes in Oregon, are also highly charged with saline matter, and are remarkable for the amount of sodium and potassium salts which they contain. Pyramid, Walker, Winnemucca, and Carson lakes in Nevada, as well as many smaller lakes throughout the Great Basin, are also without outlets, but yet, contrary to what we would expect, they hold but comparatively small percentages of saline matter in solution. Other lakes, which indicate still more pointedly the contrast between an arid and a humid climate, we may call playa-lakes. These are sheets of shallow water, covering many square miles in the winter season, but evap- orating to dryness during the summer, their beds becoming hard, smooth mud-plains or playas. In many instances a lake is formed on a playa dur- ing a single stormy night, only to disappear beneath the next noonday sun. When the weather is unsettled these lakes are scarcely more permanent than the delusions of the mirage, but come and go with every shower that passes over the land. Other playa-lakes retain their integrity for a longer period, and only become dry during excessively arid seasons. Examples of these are furnished by Honey Lake in California, North Carson Lake (“Carson and Humboldt Sink”) in Nevada, and Sevier Lake in Utah, all of which have been known to become dry during the past few years. The water of playa-lakes has a greenish yellow color, due to the extremely fine silt which is held in suspension and not allowed to settle, because every breeze stirs the shallow alkaline water to the bottom. A remarkable lake of this class is sometimes formed inthe northern part of the Black Rock Desert, in Nevada, during extremely wet seasons. Its water is furnished mainly LAKES OF THE GREAT BASIN. il by Quinn River, and it has been known to have a length of 50 or 60 miles, with a breadth of 20. During the summer it disappears entirely, leaving an absolutely barren plain of mud, Quinn River at the same time shrinking back a hundred miles towards its source. The peculiar history of playas and playa-lakes will be more fully described in connection with the physi- ography of the Lahontan basin, which is the subject of Chapter II. A few lakes situated on the borders of the Great Basin have outlets, and discharge their surplus waters into reservoirs at lower levels within the area of interior drainage. These are of the same type as the ordinary lakes of humid climates, with waters as pure and fresh as springs and melting snow can furnish. Their finest example, Lake Tahoe, lies just within the western rim of the Great Basin, at an elevation of 6,247 feet, amid the peaks of the Sierra Nevada. Its outlet, the Truckee River, flows downward with a descent of 2,400 feet to Pyramid and Winnemucca lakes, where the water is evaporated, leaving the lower lakes charged with scda salts. Just within the eastern border of the Great Basin lie Bear Lake and Utah Lake, the former discharging its waters through the Bear River and the latter through the Jordan River to Great Salt Lake. These streams carry down from the mountains their small percentages of saline matter, as a contribution to the already saturated solution of the inland sea where. their waters are evap- orated. Tt may be taken as a rule that all lakes which overflow are fresh, and all lakes which do not find outlet become in time charged with mineral salts. River water is never absolutely pure, but contains a small percent- age of mineral matter, which is left behind when the water is evaporated. Should this process continue long enough it is evident that a lake without an outlet would in time become a saturated solution, from which the less soluble mineral salts would begin to crystallize. The examination of those inclosed lakes of the Great Basin that are comparatively fresh, and especially of the lakes occupying the Lakontan basin, shows that salt lakes may in some instances become essentially fresh without overflowing. It has been suggested by Mr. G. K. Gilbert, in expla- nation of this apparent anomaly, that a lake may evaporate to dryness and its salts become buried beneath the deposits of playa-lakes, so that on the 12 GEOLOGICAL HISTORY OF LAKE LAHONTAN. return of humid conditions the water that reoccupies the old basin may be comparatively, if not absolutely, fresh. To the artist the scenery of the arid lands of the Far West contrasts with that of more humid regions by the russet-brown desolation of the valleys, the brilliant colors of the naked rocks, and the sharp, angular out- lines of the mountains. A country without water is necessarily a desert, while with abundant moisture, at least in tropical and temperate latitudes, it becomes a garden of luxuriant vegetation. In the most desert portions of the Great Basin the annual precipitation does not exceed four inches, while in the valleys on the borders of the basin it probably reaches 20 or 30 inches. Throughout this region the only fruitful areas are along the margins of streams, or where springs come to the surface. In such places, where water can be had for irrigation, one finds oases of delicious shade, with green fields and orchards yielding an unusually abundant. barvest. Thus in nearly all its physical features the Great Basin stands in marked contrast with those favored lands where rain is more abundant and more evenly distributed. The rainfall that a region receives is a potent though silent factor, which controls an almost infinite series of results in its physical history and topog- raphy. Ina humid region vegetation is usually luxuriant; the rock forms are masked by forests, erosion is rapid, and the rocks are commonly buried beneath the accumulations of their own débris or concealed by layers of vegetable and animal mould that in turn are clothed with vegetation. The - hills have flowing outlines and are dark with foliage. The valleys have gently sloping sides that conduct the drainage into streams meandering through broad plains, and the whole scene has the softness and beauty of a garden. In an arid land like the Great Basin all this is changed. ‘The mountains are rugged and angular, usually unclothed by vegetation, and receive their color from the rocks of which they are composed. From the gorges and canons sculptured in the mountain sides alluvial cones descend to the plain. These sometimes have an extent of several miles, and they are steep or gentle in slope according to the grade of the streams that formed them. The valleys, even more dreary than the mountains, are without arboreal vegetation and without streams, and form a picture of desolation BRILLIANT COLORING OF ARID REGIONS. 13 and solitude. In traveling through the Great Basin one sometimes rides a hundred miles without sight of a tree, and many times that distance without finding shade enough to protect him from the intense summer sun. The bare mountains reveal their structure almost at a glance, and show distinetly the many varying tints of their naked rocks. Their richness of color is sometimes marvelous, especially when they are composed of the purple trachytes, the deep-colored rhyolites, and the many-hued volcanic tuffs' so common in western Nevada. Not unfrequently a range of voleanic mountains will exhibit as many brilliant tints as are assumed by the New England hills in autumn. On the desert valleys the scenery is monotonous in the extreme, yet has a desolate grandeur of its own, and at times, especially at sunrise and at sunset, great richness of color. At mid-day in summer the heat becomes intense, and the mirage gives strange delusive shapes to the landscape, and offers false promises of water and shade where the expe- rienced traveler knows there is nothing but the glaring plain. When the sun is high in the cloudless heavens and one is far out on the desert at a distance from rocks and trees, there is a lack of shadow and an absence of relief in the landscape that make the distance deceptive—the mountains appearing near at hand instead of leagues away—and cause one to fancy that there is no single source of light, but that the distant ranges and the desert surfaces are self-luminous. The glare of the noonday sun conceals rather than reveals the grandeur of this rugged land, but in the early morn- ing and the near sunset the slanting light brings out mountain range after mountain range in bold relief, and reveals a world of sublimity. As the sun sinks behind the western peaks and the shades of evening grow deeper and deeper on the mountains, every ravine and canon becomes a fathomless abyss of purple haze, shrouding the bases of gorgeous towers and battle- ments that seem incrusted with a mosaic more brilliant and intricate than the work of the Venetian artists. As the light fades and the twilight deepens, the mountains lose their detail and become sharply outlined sil- houettes, drawn in the deepest and richest purple against a brilliant sky. ‘The word tufa is used throughout this yolume to designate deposits of calcium carbonate. When the volcanic product is meant, for which the same name is sometimes used, we shall designate it by the word tuff. 14 GEOLOGICAL HISTORY OF LAKE LAHONTAN. The succession of seasons is less plainly marked on the deserts of the Great Basin than on the forest-covered hills of the Atlantic slope. As autumn advances, but little change appears in the color of the landscape, excepting, perhaps, a spot here and there of gold or carmine high up on the mountains, where a clump of aspens or of dwarfed oaks marks the site of a spring that trickles down and loses itself among the rocks. The valleys with their scanty growth of sage remain unchanged, as do the dusky bands of pines and cedars on the higher mountains. As the autumn passes away, the skies lose their intense blue, and become more soft and watery, more like the skies of Italy. The hues of sunset appear richer and more varied, and during the day cloud masses trace moving lines of shadow on the surface of the desert. By and by storm-clouds gather in black, gloomy masses that envelop the ranges from base to summit. These early storm- clouds cling close to the mountains and yield to the parched deserts but a few scattered drops of rain. The observer from below hears the raging tempest amid the veiled peaks, while all about him is sunshine. The — mountains wrapped in impenetrable clouds, the glare of lightning and the deep roll of thunder as it echoes from cliff to cliff and from range to range, bring to mind the scriptural account of the storms of Sinai. And when the black clouds at last roll back from the mountains, and the sun with a wand of light dispels the storm, behold what a transfiguration! The peaks are no longer dark and somber, but glitter with the silvery sheen of freshly fallen snow. As winter approaches, the storms amid the uplands become more frequent, until every range is white as snow can make it, and the tent-like mountains gleam like the encampment of some mighty host. Long after they are covered, the valleys between are bare as in midsummer, and the snow seldom lies upon them for more than a few days at a time. The highlands retain their snow far into summer, but on none of the ranges can it be said to be perpetual. In the valleys there are flowers beneath the sage-brush by the middle of April, but from that time until November scarcely a drop of rain falls. For many days and sometimes for weeks the skies are without a cloud. EARLY DISCOVERIES. 15 The agriculture of this arid region is restricted to those scanty areas of land that can be irrigated. Of more importance is the grazing of sheep and cattle on the bunch-grass that frequently abounds amid the mountains and sometimes grows beneath the sage-brush. The mines of the precious metals, however, are the principal source of wealth, and to them must now be added a growing industry in salt, borax, sulphur, and carbonate of soda. The Great Basin is not attractive to the pleasure-seeker, but to the geologist it is peculiarly fascinating, both because the absence of vegetation to) gives such unusual facilities for investigation, and because of the character of the problems to be solved. It is in this inhospitable region, now so arid that many a lost traveler has perished from thirst, that the great lake existed in recent geological time, which has been made a subject of study by the writer and his associates, the results of which are now presented. EXPLORATIONS. The existence of a great area of interior drainage on this continent, similar in many ways to the desert region of southern Asia, was not known, except to the early Spanish missionaries, among whom the name of Father Escalante is most prominent, and to trappers and hunters, who left no records of their observation, until Capt. B. L. KE. Bonneville reached its eastern border in 1832.” A year later, a party led by Joseph Walker trav- eled across to the Pacific coast, by way of the Humboldt River and the Carson Desert. This expedition returned by a more southern route, and determined that much of the country explored did not drain to the ocean. Ten years later, J.C Fremont, then a lieutenant in the Army, carried his bold explorations into the same region, and gave the name of ‘The Great Basin” to the rugged and arid country which he traversed westward of the Rocky Mountains. A comprehensive, and, for the most part, an accurate, description of the general features of the Great Basin, was pub- lished by. Fremont in his report of 1848 ;° a detailed narrative of his jour- neys in 1842, 43, and ’44 having been published three years previously.* 2 Adventures of Captain Bonneville, by Washington Irving. 3 Geographical Memoir upon Upper California, Washington, D. C., 1848, p. 7. 4Exploring Expedition to the Rocky Mountains. Washington, 1845. 16 GEOLOGICAL HISTORY OF LAKE LAHONTAN. A summary of the results of exploration in this region previous to 1857 was prepared by Lieut. G. K. Warren, and published in Volume XI of the Reports of the Pacific Railroad Explorations, to which we must refer the reader for detailed information in this connection. A portion of the region of interior drainage is within the boundaries of California, and came within the limits of the explorations of the geological survey of that State, carried on under the direction of Prof. J. D. Whitney. Volume I of the reports of that survey contains a brief account of the Great Basin,’ relating principally to its southern border, which was compiled from the notes of several travelers. Since the completion of railroad communication with the Pacific coast in 1869, important advances have been made in our knowledge of the Great Basin. The Central and Southern Pacific railroads have crossed it and sent numerous branches through its desert valleys, both northward and south- ward from the trunk lines; many towns and mining camps have sprung up along these highways, and almost every foot of easily irrigable land has been appropriated by settlers. Herds of cattle and sheep find subsistence on the mountains and in the sage-brush-covered valleys which were once thought to be too barren to become of service to man. Some of the most productive silver mines in the world have been developed in this inhospita- ble region. ‘Throughout the eastern border of the Great Basin, in Idaho, Utah, and Arizona, the followers of the Mormon faith have found a “ prom- ised land,” which by untiring toil and industry they have reclaimed from its primitive desolation and made the home of thousands. With all this advancement, however, the Great -Basin is but thinly settled, when we consider its vast area; but, owing to its desert nature, probably contains a larger population than its agriculture alone can sustain. ‘Together with the settlement of the country, exploration has gone forward until but little of the great terra incognita of thirty years ago remains unmapped; scarcely more than a beginning has been made, however, in unraveling its compli- cated geological history. The United States Geological Exploration of the Fortieth Parallel, in charge of Clarence King, mapped the geology of a belt 100 miles wide across its northern portion A large part of the Great 5Page 461. EXPLORATION OF THE LAHONTAN BASIN. 17 Basin was also mapped by the surveys in charge of Capt. George M. Wheeler and Major J. W. Powell; and geological explorations have been carried over large areas by the geologists connected with these surveys. The present Geological Survey has made special studies of a few of the principal mining centers of the Great Basin, and commenced the investigation of its surface geology in a systematic manner. Even with such a favorable beginning, many years of patient investigation, accompanied at times with hardships and privations, will be required before the geology of the Great Basin can be fully written. The exploration of the Lahontan basin, so far as is definitely recorded, began im 1833, when it was crossed by the party in charge of Joseph Walker, as previously mentioned. No report of this journey has been published excepting in Irving’s attractive book describing the adventures of Captain Bonneville. In 1843, 744, ’45, and ’46, Fremont traversed the La- hontan basin throughout nearly its entire extent from north to south and made many geographical discoveries; but although he noted the presence of tufa deposits about Pyramid Lake, and published a sketch of the tufa- coated island which suggested its name, he does not seem to have recog- nized that his route led through the desiccated bed of an ancient inland sea. In 1854, Capt. KE. G. Beckwith’ crossed the northern part of the Lahontan basin, in the region of the Black Rock and Smoke Creek deserts, but gave little attention to the geology of the country traversed; the main object of his exploration being the discovery of a practical railroad route to Cali- fornia. Other reports of a similar nature might be cited, as that of Capt. R. Ingalls,’ who traversed the Lahontan basin in the latitude of the Carson Desert. in 1855; little information of geological importance is contained, however, in the narratives of these earlier expeditions. The exploring party in command of Capt. J. H. Simpson® entered the Lahontan basin at Sand Spring Pass, at the eastern end of Alkali Valley, in June, 1859, and encamped on the slough connecting North and South Car- son lakes; the expedition then proceeded southward to Walker Lake, by 6 Pacific Railroad Reports, Washington, D. C., 1861, Vol. II. TCongressional Documents: 34th, Ist, H. R. Ex. Doc. 1, p. 156. SExplorations Across the Great Basin of Utah, Washington, D. C., 1876, pp. 312, 313. Mon. xI—2 18 GEOLOGICAL HISTORY OF LAKE LAHONTAN. way of Allen’s Springs, and afterwards traversed Mason and Carson val- leys, which, as we now know, were also occupied by the waters of Lake Lahontan. The presence of ancient water lines and of calcareous tufa deposits about the borders of the Carson Desert was recorded by Henry Engelmann, the geologist of the expedition, in his report on the geology of the country traversed during the reconnaissance, but time did not per- mit an extended study of the surface geology of the region. That large portions of the area of interior drainage had at no distant time been occupied by lakes was clearly recognized, and the cause of their disappear- ance was correctly ascribed to climatic changes. During the progress of the United States Geographical Surveys west of the 100th Meridian, in charge of Capt. George M. Wheeler, large por- tions of the Lahontan basin were topographically surveyed, but no report on the geography or geology of the region has been published. ‘The maps prepared by this survey, and also those issued in connection with the exploration of the Fortieth Parallel, were exceedingly useful during the field work of the present investigation, and were freely used in compiling the pocket map accompanying this report, as well as in preparing some of the smaller illustrations. The expleration of the Fortieth Parallel included a belt 100 miles wide which crossed the Lahontan basin, but left considerable areas both to the north and south unmapped. In the reports of that survey Lake Lahontan received its name, and it is discussed to considerable length by the geologist in charge (Vol. I). Many detailed observations relating to the history of the former lake were recorded by Messrs. Arnold Hague and 8. F. Emmons as a part of their report (Vol. IL) of field observations. It is not necessary to introduce an abstract of the results reached by these geologists in reference to the history of the former lake, as we shall have frequent occasion to refer to their work in the pages that follow. In 1872 Dr. James Blake made a journey from Winnemucca, Nevada, to the Pueblo Mountains, Oregon, during which he traversed the northern portion of the Lahontan basin, and made many observations in reference to tufa deposits, terraces, fossil shells, etc. The results of these observa- tions were published in two brief papers in Vol. [V (1872) of the Proceedings WORK OF THE PRESENT SURVEY. 19 of the California Academy of Sciences.’ In these papers the possibility of an outlet to the ocean for the waters of the Great Basin during the Quaternary is suggested, and measurements are given of the altitude of some of the passes in the northern part of Nevada which lead towards the drainage of the Columbia. That the passes in this region could not have furnished a point of discharge for Lake Lahontan will be shown in the following chapter (page 34). The study of the surface geology of the Great Basin, undertaken by the United States Geological Survey, was begun in the summer of 1880; a section of the survey, entitled the ‘Division of the Great Basin,” having - previously been organized under the leadership of Mr. G. K. Gilbert, with headquarters at Salt Lake City, Utah. The first field season was occupied with the study of Lake Bonneville, the results of which have been pub- lished by Mr. Gilbert in a somewhat popular essay in the second annual report of the survey; the final report, in the form of an independent mono- graph, is now in preparation. In April, 1881, the writer commenced a geological reconnaissance through the northern part of the Great Basin, during which the northern half of Nevada was crossed and recrossed, and excursions were made into eastern California and southern Oregon. As the first year’s exploration was entirely of a preliminary character, without scientific assistants, all detailed study and instrumental work was deferred until the following season. ‘The reconnaissance of 1881 occupied seven months, during which about 3,500 miles were traversed in the saddle, the route being planned with special reference to the study of Quaternary geology. During the season the basin of Lake Lahontan was crossed in various directions and much of its history was deciphered. A sketch of the geology of Lake Lahontan, so far as determined from the first season’s explorations, was pub- lished in the Third Annual Report of the United States Geological Survey. While carrying forward the reconnaissance of 1881, the Mono basin, California, was visited and the study of its geological history begun; this task was left unfinished, however, until the region could be topograph- *On the absence of a rim to the Great Basin to the west of Pueblo Butte, p. 223. Remarks on the Topography of the Great Basin, pp. 276-278. 20 GEOLOGICAL HISTORY OF LAKE LAHONTAN. ically surveyed. T'rom the experience gained during the first season’s work, a plan of investigation was developed which was carried out during the summers of 1882 and 1883. On taking the field at Winnemucca, Nevada, in the spring of 1882, I was joined by Mr. Willard D. Johnson, of Washington, D. C., who accom- panied me on a journey through that portion of the Great Basin that lies north of the hydrographic rim of Lake Lahontan and is situated mostly in Oregon. The results of this exploration, so far as the surface geology of the region is concerned, were published in the Fourth Annual Report of the United States Geological survey. During this reconnaissance the pre- vious conclusion that Lake Lahontan did not overflow northward was fully confirmed. The Great Basin north of the Nevada-Oregon boundary, in common with the main area of interior drainage, is divided into a number of independent hydrographic basins, many of which held Quaternary lakes that must have been contemporaneous with the great lakes of Utah and Nevada On returning to Winnemucea in July, I was jomed by Mr. W J McGee as geological aid, and a few weeks later by Mr. George M. Wright, also in the same capacity. Proceeding southward from Winnemucca we examined the Lahontan sediments, terraces, tufa deposits, ete., occurring in the Hum- boldt Valley, and then continued our journey southward in order to study the region about Humbolt, Pyramid, Winnemucca, and Walker lakes. Later in the season we entered the Mono Lake basin and began a detailed investigation of its Quaternary geology. Owing to the advance of winter we were obliged to leave the completion of this work until another season. During the time that the expeditions mentioned above were being car- ried forward, Mr. A. L. Webster, assisted by Mr. Eugene Ricksécker, was engaged in making a topographical survey of the northeast portion of the Lahontan basin, in order to complete the compilation of the accompany: ing pocket map. The region surveyed by Mr. Webster embraced about 8,464 square miles, and is indicated on Plate IL; the extreme eastern limit of the area surveyed is a few miles to the eastward of the right-hand bor- der of the plate. LAHONTAN PL. II KE LA U.S. GEOLOGICAL SURVEY UM al ee, Lith Julius Bien & Co ROUTES TRAVELED AND AREAS SURVEYED. Routes by Sctentific Assistants Routes by I. C. Russell ~~ 29 miles «Linch Seale Areas surveyed Lahontan Beach-~ EXPLORATION OF THE MONO BASIN, 21 The various routes followed by myself and my scientific assistants during the exploration of Lake Lahontan are shown on Plate II, and will serve to indicate the degree of completeness to which we were enabled to carry our observations. A portion of the field season was devoted by Mr. Johnson to the preparation of local maps, the positions of which are also indicated on map forming Plate IT. The winter of !882—’83 was passed at the survey office in Salt Lake City, in the preparation of notes and maps for publication, chemical studies connected with our work, ete. In July, 1883, I again took the field in company with Mr. Johnson, and recommenced work in the Mono basin. After devoting all the time practicable to the study of the Quaternary geology of that region I journeyed northward and passed through a large portion of the Lahontan basin, en route to Red Bluff, California, where I disbanded my party in October. In traversing the Lahontan basin I visited several points of interest in the Walker River canon, about Pyramid and Winnemucea lakes, and on the Black Rock and Smoke Creek deserts, thus being able to review many previous observations. Mr. Johnson completed his topographical survey of the Mono basin late in December, and brought to a close, at least for the present, the field study of the Quaternary geology of the region from which the Division of the Great Basin derived its name The explorations conducted by the writer have embraced three field seasons, a part of each having been devoted to the study of Lake Lahontan. The observations made during these several journeys, so far as they relate to the great Quaternary lake of northwestern Nevada, are included in the present report. Our work in the Mono basin during the same years that the explora- tion of Lake Lahontan was being carried forward includes a study of the existing lake and of the ancient lake of much greater extent that formerly occupied the same valley; also, the relations of both the ancient and the modern lake to the glacial and volcanic phenomena displayed on a grand scale in the same basin. The results of these studies will be published in the Sixth Annual Report of the United States Geological Survey. 22 GEOLOGICAL HISTORY OF LAKE LAHONTAN. Incident to our geological studies in the Mono basin was a visit to the glaciers now existing amid the lofty peaks of the Sierra Nevada, on its western border. A sketch of the observations relating to these glaciers, together with a summary of what has been published in reference to these and other glaciers of the United States, was issued in the Fifth Annual Report of the United States Geological Survey. = OHAP TE RELY. GENESIS OF LAKE LAHONTAN. THE FORMATION OF LACUSTRAL BASINS. The discussion of the origin of lake basins has been carried on with so much zeal during the past fifteen or twenty years that we now possess a large amount of literature bearing on the subject. From the facts gathered by many observers, in widely separated localities, it is evident that the de- pressions holding lakes are extremely diverse in character and have resulted from many causes. In some instances lakes are held in basins produced by orographic movement, 7. e., by the unequal folding of rocks, by dislocation due to faulting, etc. Others are the result of erosion, and have for their typical example a rock-basin produced by glacial action. Again, there is a third great group of basins produced by the damming of pre-existing water- ways; as, for example, when the drainage of a valley is obstructed by moraines, land-slides, lava-flows, alluvial deposits, ete. 0 Following the schedule prepared by Davis,’? we have three broad classes of lake basins: a. Constructive or orographic basins. b. Destructive or erosion basins. c. Obstructive, barrier, or inclosure basins. Each of these generic divisions is abundantly illustrated in the Great Basin. Very large portions, if not the entire area of interior drainage, have 10 Classification of Lake Basins, by W. M. Davis: Proceedings of the Boston Society of Natural History, Vol. XXI, 1882, p. 321. 23 24. GEOLOGICAL HISTORY OF LAKE LAHONTAN. been broken by a vast network of fractures accompanied by a tilting of the included blocks, which have given origin to orographic basins on a grand scale. On the borders of the region, in the glaciated valleys of the Sierra Nevada and Wasatch mountains, rock basins due directly to the erosion of glaciers may be counted by hundreds if not by thousands. From almost any of the peaks of the High Sierra more than a. score of lakes of this char- acter may be observed. Lakes occupying barrier basins are also numerous in the canons of the Cordilleras where ancient moraines obstruct the drain- age. A number of the Sierra Nevada lakes which owe their origin to ero- sion and decomposition, resulting mainly from glacial action, will be de- seribed in connection with the Quaternary history of the Mono basin in the Sixth Annual Report of the United States Geological Survey. At pres- ent we are constrained to confine our attention to the more central portion of the Great Basin The aréa formerly occupied by glaciers in this region is very limited, and as flowing ice has been the principal agent in the for- mation of basins of erosion, this type of lake-basin is wanting, except about the summits of some of the highest of the basin ranges. Barrier basins, produced by the deposition of the current-borne debris of ancient lakes in such a manner as to obstruct the drainage of valleys, are not uncommon in the interior portion of the Great Basin, but the depressions characteristic of the region are due to other causes. ORIGIN OF THE LAHONTAN BASIN. The more pronounced topographic features of the Great Basin have been found to be the result of orographic displacement. The typical mountain structure of the region is monoclinal; the elements being oro- graphic blocks bounded by faults, and so tilted that their upturned edges form mountain crests with a steep descent on one side and a more gentle slope in the opposite direction. The upheaved edges of faulted blocks usually appear as long and narrow ranges. ‘Their depressed borders under- 7 GREAT BASIN STRUCTURE. 29 lie valleys. An ideal cross-section of the mountains and valleys of the Great Basin is shown in the following diagram: : a ] Seat Ww \ z \ / E Fic. 1.—Ideal section illustrating Great Basin structure. The structure here illustrated has been found so typical of the region between the Sierra Nevada and the Rocky Mountains, that it has been named by Gilbert the “Great Basin system” of mountain structure." The grandest displacements of the Great Basin are those determining its eastern and western borders, 7. e., the Wasatch and the Sierra Nevada faults. The first has been described by King, Gilbert, and others, and has been traced by the writer continuously for more than 150 miles; the second has been studied at intervals for over 200 miles without determining its full extent. The Sierra Nevada fault is much less regular in its course, and is more complex than the corresponding displacement along the eastern border of the Great Basin. It is conspicuous in Honey Lake Valley, California, where its scarp forms a line of rugged cliffs, bordering the plain on the west; and again along the west side of Hagle and Carson valleys, from near Carson City southward for fifty miles or more. In the valley of Mono Lake it is strongly pronounced; farther southward, in Owen’s Valley, it has again been recognized, but its southern, like its northern terminus, is at present unknown. ‘The details of this profound fracture are far from being understood, as it branches and changes its course in an extremely irregular manner. Disregarding all minor displacements, as well as the results of erosion and sedimentation, we may consider the Sierra Nevada in a general way as the upraised edge of an orographic block, having its eastern border determined by the great fault we have noticed above. The desert region stretching eastward from the base of the mountains is the thrown side of the same displacement. It is on the depressed side of this fault that the Lahontan basin is situated. U.S. Geographical Surveys West of the 100th Meridian, Vol. III, p. 21. 26 GEOLOGICAL HISTORY OF LAKE LAHONTAN. It is not to be understood, however, that the old lake basin was formed by a single, simple displacement; on the contrary, it is the result of exceed- ingly complex faulting that affected the entire region included between the Wasatch and the Sierra Nevadamountains. The time when these movements began is unknown, but they antedate the Quaternary, were in process during the existence of lakes Bonneville and Lahontan, and probably have not yet ceased, as will be shown in Chapter X. The old lake basin, instead of being a simple orographie valley, is composed of a large number of separate and independent depressions of the Great Basin type, which are united with one another directly, or by the intervention of narrow passes, and so nearly coincident in level that a single lake 900 feet deep in the lowest depression could flood them all. It is to the union of these various, inde- pendent, monoclinal valleys that the extremely irregular outline of Lake Lahontan is due. Nearly all the ranges of northwestern Nevada are rugged and form serrate crests having an approximately north and south trend, and, as already stated, as a nearly universal rule they are monoclinal. An older structure, however, as first recognized by King,” is frequently apparent, in which a folding of the rocks into anticlinal and synclinal may be traced. In the older deformation the rocks were crumpled and contorted as in the Alleghanies and the Alps, but during the later disturbances they were broken without being folded. The monoclinal blocks resulting from the second disturbance are the elements giving character to the present topography ; the surface features due to the former structure having been rendered inconspicuous by the later movements. The trend of the fault lines, and consequently of the mountain axes, is in general nearly north and south, but in the central part of the Great Basin, north of latitude 37°, it is more nearly north-northeast and south-southwest. . At present we can only call attention to a few characteristic examples of the displacements that gave origin to the Lahontan basin; these may be taken as types of the prevailing structure of the region. — In the Santa Rosa Mountains, in northern Nevada, the fault determining the trend of the range follows its western base and has a throw of not less 2U. §. Geological Exploration of the Fortieth Parallel, Vol. I, p. 735. FAULT BASINS. 27 than 5,000 or 6,000 feet. The eastern slope is comparatively gentle, and conforms in a general way with the inclination of the beds of voleanic rock composing a large part of the mountains. The bold western mountain face is in reality an eroded fault scarp; the thrown block underlies Quinn River Valley. In the case of the Jackson Range the principal fault follows its western ' base; the eastern base of the Pine Forest Mountains is also a precipitous fault scarp; the Black Rock Desert, intervening between these ranges, is a depressed area, which has been deeply buried beneath the sediments of Lake Lahontan. An ideal section from east to west, through these ranges, is shown in the following diagram: Pine Forest Mz Vackson Aang O_o poser __ [C0 Ww = = —————— SSS = ——— Fic. 2.—Ideal section through the Black Rock Desert, Nevada. The Pahute Range, on the eastern border of the Carson Desert, has a well defined line of displacement along both the eastern and the western base, as indicated in the following generalized section: . Panure Range Osobb Valrey. Fic. 3.~—Ideal section of the Pahute Range, Nevada. Great faults may also be traced along the western bases of the West Humboldt and Star Peak ranges. The eastern shores of both Pyramid and Winnemucca lakes are likewise determined by fault scarps, as indicated Pyramid Lake. Winnemucca. Lake. — =x x 7 ‘ below. Fic. 4.—Ideal section through Pyramid and Winnemneca lakes, Nevada. In Walker Lake Valley the orographic structure so typical of the Great Basin is again repeated; the main displacement in this instance follows the western border of the valley and determines the abrupt eastern face of the Wassuck Mountains. The topography of the valley is well shown on Plate XV. 28 GEOLOGICAL HISTORY OF LAKE LAHONTAN. If desirable, illustrations of Basin Range structure might be multiplied almost without number, not only in the Lahontan basin, but throughout Nevada, Utah, and Arizona, and in parts of Oregon and California. On the accompanying map, Plate III, an attempt is made to represent the course of the faults that determined the main features in the present topography of the Lahontan basin. The data for completing a map of this nature, however, so as to present an accurate outline of the orography of the region, have not been obtained, for the reason that special attention has not been directed to the subject The lines of displacement that are shown have been sketched from actual observation, and serve, at least in the absence of more complete data, to indicate the vastness of the system of fractures that have given diversity to the topography of the region. Could every fault be indicated the map would be covered by an irregular network of intersecting lines. The depression formerly occupied by Lake Lahontan may be taken as the type of a compound rock-basin due to displacement, many of the minor valleys of which it is composed being examples of fault-basins of the simplest kind. GEOGRAPHICAL EXTENT. THE HYDROGRAPITIIC BASIN. During the Quaternary period, as at the present time, the region of interior drainage between the Sierra Nevada and the Wasatch mountains was divided into a large number of interior drainage areas or hydrographic basins, two of which were of large size, and have claimed special attention. These are included between the 38th and 42d parallels of latitude, and together occupy the entire breadth of the Great Basin. The one to the eastward embraced northern and western Utah, together with small portions of Idaho and Wyoming, and delivered its drainage to Lake Bonneville. The hydrographic area to the westward included the northwestern part of Nevada, together with small portions of California and Oregon, and dis- charged into Lake Lahontan. Lake Bonneville received the drainage from LAHONTAN PL Il LAKE U.S. GEOLOGICAL SURVEY Julius Bien & Co. Lith QUATERNARY FAULT LINES. PRE = 29 miles = 1inch Scale: 100 > ae QUATERNARY DRAINAGE. 29 a surface 52,000 square miles in extent; Lake Lahontan’s hydrographic basin embraced 40,775 square miles. The Bonneville basin has its lowest depression along its eastern border, now occupied by Great Salt Lake; and its form was largely determined by the Wasatch fault. In the Lahontan area the lowest depression is situated near the base of the Sierra Nevada, and the topography of the basin is de- termined, to a considerable extent, by the fault which follows the eastern base of that range. The Bonneville and Lahontan drainage areas had a common divide for about 25 miles, between the 41st and 42d parallels, and a little east of the 115th meridian. Southward of the 41st parallel the boundaries of the two great hydrographic areas diverge, the included space being divided by short mountain ranges into a number of independent basins, some of which held Quaternary lakes of considerable size. The direction of the streams in the northern part of the Great Basin shows that the area is divided by a central axis, irregular in its trend, from which the surface has a general slope, both eastward and westward, to the bases of the inclosing mountains. From the Bonneville—Lahontan divide, north of Toano, the Humboldt River flows westward through a narrow and rugged valley which crosses the structural features of the country nearly at right angles. The course of the river seems to have been determined in Tertiary times, or perhaps earlier. During the Quaternary the Upper Humboldt Valley was occupied by a stream larger than the present, which emptied into Lake Lahontan a few miles east of the present site of Golconda. Before reaching the lake, the Quaternary river received considerable additions from the north through the channels of the North Fork, Magei, Rock, and Rabbit creeks, and the Little Humboldt River. Its most important tributary, however, in ancient as in modern times, came from the southward, and flowed through the nar- row Reese River Valley. On the north the Lahontan drainage area was bordered by the rim of the Great Basin, and by a number of small and independent areas of inte- rior drainage, situated mostly in Oregon and in the northwestern corner of Nevada. On the west the divide coincided for not less than 260 miles with 30 GEOLOGICAL HISTORY OF LAKE LAHONTAN. the western rim of the Great Basin, and was determined by the crest line of the Sierra Nevada, from the eastern slope of which the lake received its ereatest tribute. The Walker, Carson, and Truckee rivers gathered the surface drainage of the mountains into previously excavated channels, which bear witness to a long period of erosion antecedent to the existence of the Quaternary lake. The divide between the waters that flowed into Lake Lahontan and the drainage of the interior basins bordering it on the south and east is extremely irregular, but is well defined throughout the greater part of its course by the crests of rugged mountains. The separate drainage systems into which the basin is divided are the Humboldt and Reese river valleys of the east, Quinn River on the north, the Walker, Carson, and Truckee rivers, together with Smoke and Buffalo creeks, and Snowstorm and High-Rock canons on the west. The boundary of the region that drained into Lake Lahontan is shown on Plate IV. Besides the areas draining into living streams there are several desert basins within the Lahontan area, as represented on Plate X XIX. One of the most important conclusions to be derived from a study of the drainage in the region of Lake Lahontan during the Quaternary period is that the country at that time had about its present topographic form, The mountains were then the same as we find to-day, excepting that the lines carved by subaerial erosions are a little deeper, the alluvial cones about their bases are slightly larger, and they have undergone very mod- erate post-Quaternary orographic movements. The canons occupied by the tributaries of Lake Lahontan still afford drainage channels when there is sufficient precipitation to form streams. If Quaternary man could revisit his ancient hunting grounds, he would have no difficulty in recognizing the landmarks that were once familiar to him. The mountains and valleys are the same, although their scanty vegetation has probably undergone many changes. The great lakes which were familiar to him, however, have passed away and given place to broad silent plains of desolation. The former rivers have shrunken, and many of their channels are dry. U.S. GEOLOGICAL SURVEY ee Pitt River LEGEND Area of lake atHighest Stage == Outhne of Hydrographic basin Western Limit of Bormeville Drainage LAKE LAHONTAN PL. Iv Map of JAKE LAHONTAN showing Water Area and boun dary of Hydrographic Basin by ISRAEL C. RUSSELL. Scale in Statute Miles. 20 3 i a | C)S << are. i ‘a = 7 ey ~* ‘* Yo = i “Be Ss \* ¥ rade Th : > | ae a ac ie eal eee = . : Lal va = ¥ = mse —< a it us a ’ yo ks ° : ‘. 4 eh p, 4 CABBS VALLEY LEGEND Area of lake atHighest Stage (es) Outline of Hydrographic basin —_ ‘Western Limit of Borneville Drainage enonn oy Nore A. Kor yoy Yxnos. - “Se 72. Pc ae co: Ts ee ee a ee Sy ee praeert epes oy Am ete Se ees edie et 6 nS ge ie A i . t 7 i _ . ‘ \\\ LAKES OF THE LARONTAN BASIN. 63 The resemblance of Pyramid Lake to an arm of the sea is enhanced by the presence of numerous sea-birds. About The Needles especially one sees large numbers of gulls, terns, cormorants, pelicans, together with geese, ducks, swans, herons, bitterns, etc. Many of these find convenient nesting places in the hollows of the calcareous tufa. During our visit to Anaho Island in August, 1882, there were two large pelican “ rookeries,” in each of which there were 600 or 800 young birds. WINNEMUCCA LAKE. This, like its sister lake, occupies a long, narrow valley, formed by orographic displacement, and is a fair illustration of a lake occupying a fault basin. It is 26 miles long, with an average breadth of about 34 miles, the longer axis being due north and south. As in the case of Pyramid Lake, its waters are alkaline and brackish. The following analysis by Prof. F. W. Clarke is of a sample collected in August, 1882, near the center of the lake (at c, Plate IX) and 1 foot below the surface: : —: : : | One liter of | i Probable com- c | water con- | Per cent. in . bination (in Constituents. | tains in | total solids. | Constituents. grammes per grammes— | liter). = —— l= = a —— Sthiaa(SiOs) haces eee tee eee 0. 0275 ONTO TSilicat(SiOs eames he eee 0. 0275 Magnesium (Mg) ---..- .----.-- ------ 0.0173 , 0.48 || Magnesium carbonate (MgCOs) ---.-.| 0, 0494 Galemim\(Ca)ieeos oo = Sse ee eee eee 0. 0196 0.54 | Caleium earbonate (CaCO3) ...---.--. 0. 0254 Sodium (Na) .---.-- 1. 2970 | 36.00 |! Potassium chloride (KCI) ...-..- =eet|) 0.1310 Potassium: (Ks ---2-- 2 o-oo es 0. 0686 | 1.90 | Sodium chloride (NaCl) ...........-- 2. 6877 Ghlorine (Cl) S25 2-2 ase - 50 Sa cisee oatece 1, 6934 47.01 | Sodium sulphate (Na2SO,)..-..--..-- 0.1972 Sulphuric acid (SOs) ..-..------------- . 1333 3.70 | Sodium carbonate (Na2CQs) .---- 0. 4065 3. 2567 | 90. 39 Total (98.44 per ct. accounted for) - 3. 5247 Carbonic acid (COs) by difference. ----. . 3458 | 9. 61 - UNTO ee SSeS sere oman Seer | 3. 6025 | 100. 00 | | Nearly all of the water that supplies the lake enters at its southern end, and consequently causes this portion to be fresher than the northern part. As stated while describing the Truckee River, the water supplying this lake is a branch of the main stream. The only published account known to us of the bifurcation of the Truckee River, so as to supply two lakes, is given by Mr. King,* who states that— At the time of our first visit to this region, in 1867, the river bifurcated; one balf flowed into Pyra- mid Lake, and the other through a river four or five miles long into Winnemucca Lake. At that time 28U. S. Geological Exploration of the Fortieth Parallel, Vol. I., pp. 505-6. 64 GEOLOGICAL HISTORY OF LAKE LAHONTAN, the level of Pyramid Lake was 3,890 feet above the sea, and of Winnemucca about 80 feet lower. Later, owing to the disturbance of the balance between influx and evaporation already alluded to as expressing itselfin Utah by the rise and expansion of Great Salt Lake, the basin of Pyramid Lake was filled up, and a back water overflowed the former region of bifurcation, so that now the surplus waters all go down the channel into Winnemucca Lake, and that basin is rapidly filling. Between 1°67, the time of my first visit, and 1871, the time of my last visit, the areaof Winnemucca Lake had nearly doubled, and it has risen from its old altitude about 22 feet, Pyramid Lake in the same time having beeu raised about 9 feet. The outlines as given upon our topographical maps are according to the survey of 1867, and form interesting data for future comparison. The differences in elevation between Pyramid and Winnemucca lakes, as reported by Mr. King, and as determined by the present survey in August, 1882, are as follows: In 1867 Pyramid was 80 feet higher than Winnemucea (U. 8. Geol. Expl. 40th Parallel, Vol. I, p.505); in 1872 Pyra- mid was 67 feet higher than Winnemucca (U S. Geol. Expl. 40th Parallel, Vol I, p. 506); in 1882 Pyramid was 12 feet higher than Winnemucca, as determined by engineer's level. We know of no accurate means of determining how much each lake individually has varied since 1872, but the decrease in the difference of the levels of the two lakes is certainly due in part to the lowering of the waters of Pyramid Lake, as is indicated by recent tufa deposits and lines of bleached sea-weed at an elevation of about 12 feet above.the present surface of the lake. From the data now in hand, providing that all the measurements are correct, it is evident that Winnemucca Lake has risen over 40 feet since 1872, and over 50 feet since 1867. The history of the fluctuations of these lakes is supplemented and en- larged by the statements of Mr. George Frazier, who has been familiar with the region since 1862 In his judgment Winnemucca Lake has risen about 40 feet in the last twenty years. In 1862, the branch of the Truckee River that supplies Winnemucca Lake was so low that a person could cross it by stepping from stone to stone, at a point where it is now not less than 25 feet deep. The lake was then confined to the northern extremity of its basin, and the stream reached it after meandering through meadow lands that are now 15 or 20 feet under water. At that time the channel of the stream could be traced along the bottom of the lake for some distance, and dead cottonwood trees were standing in the water, showing that the lake had previously been much lower. Dead trees standing in Pyramid Lake, some distance from the shore, bore similar evidence to the rise of that lake iy Lower Aol al rama s a LAKES OF THE LAHONTAN BASIN. 65 previous to 1862. This lake, however, is thought by Mr. Frazier to be much higher at present than when he first saw it. During the spring and summer of 1868 the Truckee delivered more water than usual, and Pyramid Lake rose 10 or 15 feet. This rise continued throughout the following year, and during these two years Pyramid overflowed into Winnemucca Lake. The water in the ‘“‘slough” at that time was brackish and unfit to drink. In the summer of 1876 all the water of the Truckee River emptied into Winnemucca Lake, its outlet into Pyramid Lake having been closed by a gravel bar; but the annual rise of the river the following spring re- moved the obstruction. These observations, although not of scientific accuracy, are yet of value, and have been confirmed by other people who have been acquainted with these lakes for a number of years. We may note here that the rise of Pyramid and Winnemucca lakes during the last fifteen or twenty years is synchronous with a similar in- crease observed in Goose, Horse, and Mono lakes, California; Walker and Ruby lakes, Nevada; Great Salt and Rush lakes, Utah. In determining future fluctuations of level in Pyramid and Winne- mucca lakes, the accompanying map, Plate IX, may be considered as of approximate accuracy; the soundings, too, were made with care. Besides these data we have determined the elevation of certain points above the surface of the lake, which will serve as bench-marks for future measure- WEST VE RS AY eS \ x \ Fas PAO) NN AEST P ung 7 ce SE ot ea = TL MT sya e ( a Theale Mm aN ee: \“ an ade a “pe PAW cS So Se aan WE TEAC A\ ONE MILE ES Fic. 7.—Portion of the east shore of Pyramid Lake, showing position of measured rocks. ments. In the southern end of Pyramid Lake, and to the eastward of the Truckee delta, rise a group of tufa crags, indicated on the map by the let- ters x, y, 2. An enlarged plat of this portion of the lake shore is given in the accompanying figure. The height of these crags above the surface of Mon, x1—5 66 GEOLOGICAL HISTORY OF LAKE LAHONTAN. the lake, September 9, 1882, was as follows: 2, 21.0 feet; y, 9.8 feet; 2, 23.7 feet. This record may’ be increased by adding the following elevations above the lake level as determined in September and October, 1882:° Summitiof:Amaholslandss5 see ete ee eee eee eee Sane 517 feet Summit of ‘‘Mushroom Rock,” on the north shore of Anaho Island (See: Plate kV). sm sede = seeie- nee yee ee eee eee ..-- 17 feet 3 inches Rock to the south of Mushroom Rock (beneath bird on Plate XIV). 8 feet 5 inches Summitiof< Pyramid island) ((Elateexs)) Rees eee eee 289 feet Highest spire among The Needles (Plate XIII).....-.............-. 300 feet HUMBOLDT LAKE. Humboldt Lake is but an expansion of the river that supplies it, and is held in check by an immense gravel embankment that was thrown com- pletely across the valley by the currents of the former lake, at one time 500 feet deep at this point. An accurate map of this structure is given on Plate XVII, and a detailed description on page —. As there described, the em- bankment has been cut across by the overflow of the lake and the breach partially filled during the past few years by an artificial dam, which has greatly increased the area of the lake. During the dry season the lake seldom overflows and is then the limit of the great drainage system of the Humboldt River, but in winter and spring the waters escape southward, and spreading out on the desert form Mirage Lake. Farther southward on the northern part of the Carson Desert they again expand and contribute to the formation of North Carson Lake. In the summer of 1882, Humboldt Lake covered an area of about 20 square miles, did not overflow, and although somewhat alkaline was inhab- ited by both fish and mollusks, and was sufficiently pure for human use. The following analysis of its waters by Prof. O. D. Allen, of Yale College, is taken from the reports of the United States Geological Exploration of the Fortieth Parallel, Vol. II, p 743. 29 All these measurements were made with an engineer’s level. YON 'HOOY WOOYHSAW SYOHS HLY OHYNY 340 NYS! (al) \\\ Z 7 _- 7 _ . 49: — "YY - ua —o—_—-— —lCEOA - = foe eee a tS LAKES OF THE LAHONTAN BASIN. 67 Constituents. 1. 2 Average. | Specifie gravity, 1. 0007. | | Fixed residue in 1,000 parts .. ....... 0. 9015 0. 9045 | 0. 9030 Constituents found in 1,000 parts: Carboniciagid\ Ss. .csccanoscennene ee 0.1065 | 0. 1075 0. 1070 SulphuriciaGitlee- ens. see 4e tere 0.0257 | 0. 0248 0. 0253 Phosphoricwoid! 2-2-5. -422-2eoss a 0. 00069 |........... 0. 00069 Chiorities 22s5 cee se nicncds esccns 0. 2954 0. 2949 0. 2952 I TCEVEC: Jas Be poOOreSeE Ba aEOeaaeeanee 0. 0320 | 0. 0330 0. 0825 MB pn Onin eects ceten fora ose nes 0. 0281 0. 0268 0. 0274 IAM OF ese PRES Cece ee 0. 0180 0. 0172 0. 0176 Sodinm@res senna nde tase enee 0. 2786 0. 2783 0. 2785 Popasuium eoree seas es. tg 0. 0612 0.0605 0. 0609 PAM arco ann sence eerie te aoa ee WACO.) O| [ic aesaecccrs | trace. Boracioaeld: .2 Fh 5s tenes costo nee US Cea Seer =o) trace. 0. 84509 OPS YE SoS Sos-crncee nse gnanescoee 0, 04273 | 0. 88782 There is probably a loss of carbonic acid. The theoretical combination of bases and acids would give— Carbonate of soda. -..._- mise ists 0, 24944 Sulphateiof'soda -. ............--... 0. 04498 Chloride of sodium ....-..........-.. | 0.39571 Chloride of potassium. —_.-. | 0.11617 Carbonate of lime .-................ | 0.03143 Carbonate of magnesia ............. | 0. 05768 [WSU Cater amen creetr a eacteras = aaa | 0. 03250 | ePhosphorio\acidjse- === ses ns | 0. 00069 0.92860 | Less carbonic acid added to the | amount found ...........-..--..... | 0 04254 i | 0. 88606 A series of soundings made in Humboldt Lake, in July, 1882, gave a nearly uniform depth of 12 feet for the central part. Near the western shore quite extensive mud-banks rise a few feet above the surface and nearly divide the lake; westward of these the water is still more shallow than in the main body. The lake is being rapidly filled by the silt from the Hum- boldt River, and is destined to early extinction. Owing to the orographic structure of the valley it occupies, the east- ern shore of the Humboldt Lake is bordered by a precipitous cliff of dis- placement, the western shore is low and marshy, in places covered with a saline efflorescence. A sample of the incrustation from the surface of the 68 GEOLOGICAL HISTORY OF LAKE LAHONTAN. desert near Brown’s Station was found by Mr. R. W. Woodward to have the following composition: Constituents. Per cent. Soluble in water ...... -----.--. = 27. 71 | Chloride of sodium ......-----..---- 49. 67 | Sulphateyorsoda’----.~ 2a ae aie 20. 88 | Sesquicarbonate of soda....-.....-- 18.15 Boraterotesod a) seem ce se aa tame 11. 30 100. 00 NORTH CARSON LAKE, This lake is situated on the northern part of the Carson Desert (see Plate VII) and receives its waters from both the Humboldt and the Carson rivers. Having no outlet, the waters flowing into it have been supposed to sink, and for this reason it is generally spoken of as the ‘‘Humboldt and Carson Sink.” As this term is based on an error, we have used the name ‘North Carson Lake” instead. During the winter and spring it receives a considerable supply of water from both the Humboldt and Carson rivers, and becomes a shallow playa- lake, between 20 and 25 miles in length, by 14 miles in breadth. In unu- sually arid summers the water supply fails, and the lake evaporates to dry- ness. As desiccation becomes more intense the salts impregnating the lake- beds are brought to the surface and form an efflorescence several inches in thickness. This was the case when the Carson Desert was visited by the writer in October, 1881. The lake had then wholly evaporated, leaving a broad mud- plain covered in places with a white alkaline crust that looked like patches of snow. SOUTH CARSON LAKE. Situated on the southern border of the Carson Desert lies South Car- son Lake. This, like the larger lake to the northward, is a playa-lake and occupies a very shallow depression in the lake-beds flooring the desert. Like other lakes of its class, it has indefinite boundaries and varies in size 30, $. Geological Exploration of the Fortieth Parallel, Vol. I, p. 744. LAKES OF THE LAHON'TAN BASIN. 69 and depth with the alternation of seasons. In 1882 its area was about 40 square miles, with a depth of four feet throughout its central portion. Its waters are alkaline, and contain 1.4725 grammes of solids in solution to the liter; of which 0.2135 gramme is silica, as reported by Prof. F. W. Clarke from a partial analysis of a sample collected in October, 1863. The lake is supplied almost entirely by the Carson River and usually overflows through a slough into North Carson Lake.” The low muddy shores are strewed with the dead shells of Anodonta Planorbis, Limneea, ete., but, so far as known, no mollusks are now living in the lake. WALKER LAKE. The southern extremity of the Lahontan basin is occupied by Walker Lake, which, next to Pyramid Lake, is the most picturesque and attractive of the desert lakes in the Lihontan basin. A correct outline of the lake, as it existed in 1882, is given on Plate XV. As may be gathered from the map, the lake is 25.6 miles in its longer, or north and south axis, and has an average width of between 4.5 and 5 miles. Its area is 95 square miles As on the map of Pyramid Lake, the actual soundings are given in figures, and the somewhat conjectural topog- raphy of the bottom is represented by dotted contour lines. Over a large area in the central and western portions it has a remarkably uniform depth of 224 feet; but as a rule the depth increases as one approaches the west- ern shore, which is overshadowed by rugged mountains. The bottom throughout the central portions is composed of fine tenacious mud, which in many places is black in color, and has the odor of hydrogen sulphide. Coarser deposits, consisting of sand and gravel, mingled with the empty shells of Pyrgula, Pompholyx, ete., were found only in the immediate neigh- borhood of the shore. No mollusks were found living in the lake; but the conditions of environment being so similar to what has been observed in Pyramid Lake, it is thought that a more careful search would show that Walker Lake is also inhabited by a few species. Analyses of the water, collected in September, 1882, one foot and 215 feet below the surface 31 See ante, page 44. 70 GEOLOGICAL HISTORY OF LAKE LAHONTAN, where the depth was 224 feet, as shown on the accompanying map, are re- ported by Prof. F. W. Clarke as follows: aan ; Probable com- neliterof water) y_.. . bination (ex- | contains, in| E ate pressed in ! gramm«s— : a grumufes per | | liter). eSear we | 5 = =e |e rte is) ee mt wo Constituents. 265 ae Constituents. 5 née i=} D | = DQ 8 a QD | SE | Be cE Ee a6 AS tele, 9 |) SS o bali i aS heen | Rpt o2 , | 92. | Bes | Gas ass S08 Bee | das | Bos | bee | oe nh n Sificay(SiQe) isco sneer es 0. 0075 0, 0075 0.29 | 0.30 Sil08) (S102) Peete seriall eat | 0.0075 0.0075 Magnesium (Mg) .--- 0. 0391 0. 0375 DD) 1.51 | Magnesium carbonate (MgCOs).-- 0.1369 | 0.1313 Calcium (a) S2te--se-5 eee rel 0. 0267 0. 0176 1.96 0.71 | Caleium carbonate (CaCQOs)..---- | 0.0667 0. 0440 Sodinmil(Na) eee s-- see eee 0.8577 | 0.8530 | 34.11 | 34.29 | Sodium chloride (NaCl)-........- | 0.9681 | 0. 9558 Potassium (K).------ race. | Trace. | Trace. Trace. | Sodium sulphate (NazSOu)-.--..-- | 9.7803 0. 7580 Chlorine (Cl) ..-.--.-- F 0.5800 | 23.86) 238.32 | Sodium carbonate (NaCOs)-.-.-- | 0.5157 | 0. 5339 Sulphuric acid (S04) 0. Od) 2G | 20. 6 | 2.4752 | 2. 4305 STOOSi (RBI 83) (reo N7an | oss) eee eee ee | 0.0403 | 0 0570 7 A ars 5 = | ane Carbonic acid (CO;) by difference - . ee Dee 18, 67 | eset Pn ae *9,5155 | #2.4875 SUE ne beetec se Seats Seo De 2.5155 | 2.4575 | 100.00 | 100. 00 * 98.39 per cent. accounted for. + 97.66 per cent. accounted for. As in the case of the other lakes of the Great Basin, situated at an ele- vation of less than 5,000 feet, the shores of Walker Lake are totally lacking in arboreal vegetation except at the river mouth, and are clothed only with desert shrubs. At the northern end, and following the immediate shores of the Walker River for many miles, are luxuriant cottonwood groves, to- gether with willow-banks and meadow-lands. At the northern end, the river is building out a low delta of fine silt, and remnants of similar deltas, at higher levels, may be seen as one follows up the river. A change in the level of the lake is recorded by dead trees standing in the water, which show that it has risen at least four or five feet in recent years. The waters at a distance from the river mouth are of a clear deep blue, changing to a bright green tint near the shore, as in Pyramid Lake. They are charged with saline matter to such an extent that carbonate of lime is now being deposited. The calcareous tufa uow forming cements the gravel and sands of the shore into compact strata or forms rosette-shaped masses, with isolated pebbles for nuclei. U. 8. GEOLOGICAL SURVEY 118°45" PE T-bentan Beach = —.custral Contour, DSOMRLERALS 727 LEE“. SCALE OF MILES £ s I. C. Russell, Geoloyrot. W. D. Johnson, Topographer. LAKES OF THE LAHONTAN BASIN. 71 in the study of the recent and fossil lakes of the Far West it is fre- quently desirable to know the present rate of evaporation, and the charac- ter of the seasonal and secular variations in precipitation that are taking place. Attempts have been made to determine the rate of evaporation by experimenting with artrficial evaporating pans, but owing to the difficulty of imitating the conditions of nature, these observations have been of little value. Gauges have been established in Great Salt Lake, and accurate records of its annual and secular fluctuations have been secured for a num- ber of years, but in this instance the variations of the lake are influenced by irrigation, and the sources of supply for the waters of the lake are too numer- ous to be definitely measured. Of all the lakes of the Far West with which we are acquainted, excepting Abert Lake, Oregon, the most favorable for determining the questions indicated above is Walker Lake. As this lake receives its entire supply from a single source and is without outlet, the rate of evaporation from a large water surface could be determined with great accuracy. Observations intended to show the secular variations in precip- itation would be more difficult because the waters of Walker River are largely used for irrigation. LAKE TAHOE. As Lake Tahoe is the grandest of the Sierra Nevada lakes, and the largest that discharged into Lake Lahontan, we insert a brief account of it, compiled principally from the investigations of Prof. John Le Conte, of the University of California.” j The lake is situated in latitude 39° N., and lies part in California and part in Nevada, at an elevation of 6,247 feet, as determined by railroad surveys. Its drainage area, including the lake surface, is about 500 square miles. The water surface is 21.6 miles long from north to south, with an extreme breadth of 12 miles; its area being between 192 and 195 square r miles. Its outlet is the Truckee River, which leaves the lake through a magnificent gorge, at a point on its northwestern shore. 82“ Physical Studies of Lake Tahoe,” published in the Free Press and the Mining and Scientific Press of San Francisco, during 1880 and 1881. Reprinted in the Overland Monthly for November and December, 1°83, and January, 1384. ie GEOLOGICAL HISTORY OF LAKE LAHONTAN. _ Soundings made by Professor Le Conte, beginning at the northern end, near the ““Lake House,” and advancing along the longer axis of the lake directly north towards the ‘‘Hot Springs,” at the northern end, give depths of from 900 to 1,645 feet Between the 11th and the 18th of August, 1873, Professor Le Conte made a large number of temperature measurements at different depths in the lake, an abstract of which is here copied: | No. | Depth in Depth in Temperature: Temperature: | feet. meters. Fahr. Cent. | SUE) A) eee Seen eedllsted-Bkces Se 67 19. 44 apaiee aye 50 15. 24 | 63 17. 22 agetet ecm | 100 30. 48 | 55 12.78 | 7 yigtes ole BP 150 45.72 50 10. 00 Boe aaene | 200 60. 96 48 8.89 Gee 250 76. 20 47 8.33 Tee oa 300 91.44 46 7.78 | 8 (bottom) 330 | 100. 58 45.5 | 7.50 este eee 400 121, 92 45 7. 22 LORE ees 480 146. 30 44.5 6.94 11 (bottom) - 500 152. 40 44 6. 67 1D eter 600 182. 88 43 6.11 | 13 (bottom) .| 772 235, 30 41 5.00 | 14 (bottom) | 1, 506 459. 02 39.2 4.00 Professor Le Conte’s paper also contains many valuable observations on the transparency and color of the lake water, and on rhythmic variations of level. An analysis of the water of Lake Tahoe has already been given on page 42. Besides Lake Tahoe, there was another lake among the mountains of * Northern California during Quaternary times which was tributary to Lake Lahontan. This was a comparatively shallow water body that occupied the basin now known as the Madeline Plains. A small stream from Horse Lake Valley joined that draining the Madeline Plains; as did also the waters escaping from Eagle Lake, which, without evidence to the con- trary, we may consider to have discharged, then as now, through beds of gravel beneath a lava coulée. SODA LAKES, NEAR RAGTOWN, NEVADA. On the Carson Desert, about 2 miles northeast of Ragtown, are two circular depressions that are partially filled with strongly alkaline waters and known as the Soda Lakes or Ragtown Ponds _ By reference to the accompanying map (Plate XVI), on which the contour lines are drawn at intervals of 20 feet, it will be seen that the lakes occupy deep depressions in low cones. The larger lake is 268.5 acres in area, and the smaller is a pond of variable size.” The form of the larger depression is still farther illustrated by the cross-section given at the bottom of the plate, which has been constructed from actual measurements with an engineer’s level and a sounding line. The rim of the larger lake in its highest part rises 80 feet above the surrounding desert, and is 165 feet higher than the surface of the lake which it incloses. The outer slope of the cone is gentle and merges almost imperceptibly with the desert surface; but the inner slope is abrupt and at times approaches the perpendicular. A series of careful soundings gives 147 feet as the greatest depth of the lake. The total depth of the depression is: therefore 312 feet, and its bottom is 232 feet lower than the general surface of the desert near at hand. The walls encircling the lake exhibit well exposed sections of stratified lapilli, mingled with an abundance of angular grains, kernels, and masses of basalt, some of which are 2 and 3 feet in diameter and scoriaceous, especially in the interior. Mingled with this angular and rough material is a great quantity of fine dust-like lapilli, and some rounded and worn pebbles of rhyolite. Interstratified with the lapilli occur marly lake-beds containing fresh-water shells and dendritic tufa, as is indicated in the accompanied generalized section of the crater walls (Plate XVII, Fig. A). Both the lapilli and the lake-beds are evenly stratified, and exhibit diverse dips. On the interior of the larger crater, on the south side, the dip is towards the lake at an angle of about 30°. On the east side the stratifi- cation appears quite horizontal, but may, perhaps, be inclined away from 3% The smaller lake, when the accompanying map was made, had been so changed by excavation and the construction of evaporating vats that its original form had been destroyed. Its surface is 20 feet higher than the larger lake, and 65 feet below the general desert surface. The highest point on the crater rim is 80 feet above the bottom of the depression. 73 74 GEOLOGICAL HISTORY OF LAKE LAHONTAN. the crater; near the surface of the lake there are two planes of unconform- ability, as well as a number of small faults. In the crater walls on the opposite side of the lake a number of displacements may be seen, as indi- cated in Fig. E, Plate XVII. The form of the cones and the nature of the material of which they are composed leave no doubt that these are crater-rings, @. e., low cones of erup- tion containing large craters. The evidence sustaining this conclusion is abundant In the stratified beds of yellowish lap/flli, which are always an- gular and sometimes as fine as dust, are many fragments of basalt, rhyo- lite, and masses of hardened lake-beds,* that are evidently ejected frag- ments that have been dropped from a considerable height to the positions which they now occupy. The strata of lapilli beneath these “bombs” are bent down, as shown in the accompanying sketch (Figs. B, C, and D, Plate XVII) the disturbance being visible for 6 or 8 inches below the included rock. The strata of loose cinders covering the inclosed fragments are horizontal and undisturbed. That the cones were not formed during a single eruption, but have a long and complicated history, and are perhaps sublacustrine in their origin, is shown by the alternation of ejected and sedimentary materials in the crater walls. From the presence of fossiliferous lacustral clays in the midst of lapflli, it seems evident that voleanic eruption was interrupted by periods during which the lake covered the craters. The presence of dendritic tufa in the midst of the section proves that the volcano was active both before and after the dendritic stage of Lake Lahontan. The wall of the larger lake is some- what open on the south side, while the western rim has been prolonged southward (see Plate XVI) in such a manner as to suggest that the erupted material was in part removed by currents at the time it was ejected and deposited in the form of an embankment, connecting with the crater rim. The hypothesis that the craters were formed by the action of extremely powerful sublacustrine springs, as advanced by King,” would not account for the nature of the material forming the crater walls, nor the presence of 344 The rhyolite pebbles and fragments of lacustral sediments thrown out by this voleano were evi- dently derived from the superficial strata through which it opened a passage. The basalt, on the other hand was erupted in a semi-fused condition and formed slaggy masses on cooling. 3U, S. Geological Exploration of the Fortieth Parallel, Vol. I, p. 512. U S. GEOLOGICAL SURVEY LAKE LAHONTAN PI, XVI. ; I. C. Russell, Geologist _ W.D.Johnson, Topographer. Julius Bien & Co, Lith. ; r hes SODA LAKES NEAR RAGTOWN, NEVADA . LAKES OF THE LAHONTAN BASIN. 15 the numerous voleanic bombs that depress the strata on which they rest. If the cavities owed their origin to springs of very great magnitude rising in the bottom of Lake Lahontan, it is evident that the out-flowing waters would have cut channels of overflow when the lake evaporated to a horizon below the rim of unconsolidated material that surrounded them; but the crater walls are now continuous and unbroken by stream channels. On the other hand, had the springs become extinct before the evaporation of the lake the cavities they formerly occupied would be buried beneath lake-beds. This, as our observations show, is not the case, but both the inner and outer surfaces of the cones are free from lake sediments The last addition of lapilli to the walls of the crater must have been of post-Lahontan date. The least diameter of the larger crater at the water surface is 3,168, and its greater 4,224 feet. Its area, as stated on a previous page, is 268.5 acres. A sublacustral spring of these dimensions, rising with sufficient force to carry blocks of basalt 1 or 2 feet in diameter to the height of 150 feet, would be a phenomenon without parallel. That the lakes occupy extinct craters is recognized by Mr. Arnold Hague in his description of the Carson Desert.” There are no streams either tributary to or draining these lakes; their total water supply, excepting the small amount derived from direct precipi- tation, is supplied from subterranean sources. Around the immediate shores of the larger lake there are a number of fresh-water springs ; the largest of these is situated on the northern border of the basin, and issues from a small fault at an elevation of about !5 feet above the water surface. As the lake, by aneroid measurements, is 50 feet below the level of the Carson River at its nearest point, we may safely look to this stream as the probable source of the water supply which reaches the craters by percolating through the inter- vening marls and lapilli deposits. The bottom of the lake, as determined by many soundings, is a continuation of the slope of the inner walls of the crater, excepting that the conical form has been modified by shore action and sedimentation, which has resulted in the formation of the terrace about the present water margin. In the northern part of the lake a reef of rock pro- jects above the surface, and soundings show that this is continuous from 5°U.S8. Geological Exploration Fortieth Parallel, Vol. II, p. 746. 76 GEOLOGICAL HISTORY OF LAKE LAHONTAN, shore to shore, thus indicating that two craters are combined in the forma- tion of the present depression. The bottom, as shown by the samples obtained by the cup at the end of our sounding lead, is a fine tenacious black mud having a strong odor of sulphuretted hydrogen. When exposed to the air for some time this mate- rial loses its inky color and shows itself to be of the same nature as the fine dust-like lapflli that form a large part of the crater walls. The organic matter impregnating these sediments is evidently derived from the millions of brine shrimps (Artemia gracilis) and the larvee of black flies that swarm in the dense alkaline waters. Near the shore the rock and pebbles, as well as bits of organic matter are coated with beautiful crystals of gaylussite which form about any solid nucleus that chances to be available. The crystals are white, with trans- parent edges, monoclinic in form, and thin in the direction of the orthodiag- onal, as illustrated by Figure 607, Dana’s System of Mineralogy, 5th edition. The small island in the northern part of the lake is completely coated with gaylussite crystals and trona. An analysis of a crystal of gay-lussite from this locality by Prof. O. D. Allen gave the following composition :* GUID G yap cen ora eats A evan Pave afer Soc Tao eee Ree ae 19.19 Sl eas = | eck Se are cit ce ee es ae Rar ry a ane ee 19. 95 Garbonie*acid'}. 54 .as8s:. iociewrap eee eee eee 29. 55 NENTS th tea cece, ae PR eA ae ee Ie SENNA Aa EH Ee Pao boy UI) (nil ayia KOE Sas 4 Sansa dooms. acne osnuod Jescod Seoase Trace. hl Orin eres o fede ses ae ee ee eee ee eee Trace. Insoluble reside a le a me " iT \\77 ae TY) py Uy rae f iil HTT .. yy, A iil hh ‘ii i ERAN iy fy AANA He al H i i HM Wij, ~ iy ANNA iN i Y } Wy} y My yy, ~ WY \ I WW } y y} y YY WS ¢ \ \ \\ ‘ Ny pat Se ilises Ml y i i ANN KA A aT | Yy by f SN WN \ yi Yi} ! % f J i Mihi SSS = ——— —< ic = Se F FUipo re wy : = VS ——— = SSS — I i} HiIl = MT Hi) We WE Shh y SS= SS —= SSS — = > = ——— mail ! ail I! IZ, i { di fe zy nn th) inf mp wpiidieraa bat eee } fe! yh aH \ i { ‘Ny Sp Mihi nu I ar fy ely Pa we ) H epeobo tittle) eco reer W. D. Johnson, Topographer. T. C. Russell, Geologist. GRAVEL EMBANKMENTS AT BUFFALO SPRINGS, NEVADA, EMBANKMENTS AT BUFFALO SPRINGS. 117 heaches took place during the last high-water stage of the lake. This de- lermination, however, will appear more clear to the reader as we advance with our studies. An inspection of the map shows that all the structures there repre- sented were built in a rising lake, and were but little, if at all, modified by the waves and currents as the waters receded. This statement requires qualification however. We may be certain from the perfection of the ridges that the retiring waters did not tend to destroy them, but, on the other hand, they may have received additions. It is probable that gravel structures like those under discussion, when formed in a rising lake, would induce dep- osition at the same horizons during a recession of the waters. The sec- tions of the structures at Buffalo Springs fail to give information on this point. The only modifications that have taken place in these deposits in post- Lahontan times are due to the erosion of the rills that cross them and the partial removal of the fine sediment deposited over the older bars. At the extreme distal end of the embankment that projects into the valley there are considerable accumulations of sand, illustrating the fact that fine material is carried farthest by currents when structures of this char- acter are found, andshowing why the bottoms of gravel embankments are fre- quently composed of sand. On either slope of the embankment the gravel of which it is composed is concealed beneath fine sediments, which must have been deposited when the lake stood over the structure. The looped bars high in the series at one time contained lagoons in which mollusks found a congenial habitat, as is shown by the multitudes of shells, principally of Pompholyx, that crowd the marls in the miniature playas behind a num- ber of the embankments. Three miles south of Buffalo Springs there is another group of embank- ments similar to that described above. These are represented on the sketch- map forming Plate XXI.* 4° This map is less accurate than the one forming Plate XX, but it indicates the main features of the structures as well as could be desired. The figures on Plate XXI are from aneroid measurements, and indicate approximately the depth of water at the highest water stage of Lake Lahontan. The figures on Plate XX are from measurements with an engineer’s level, and may be considered accurate. 118 GEOLOGICAL HISTORY OF LAKE LAHONTAN, All the structures in this group were formed mainly by currents from the south, which swept along the lake shore, carrying shore drift with them, and were deflected from the land upon arriving at the place where deposi- tion had been initiated. This is shown not only by the curvature of the terraces as they approach the bars, but also by the fact that the structures are much the steeper on the north side. In these beaches and embankments, as in those at Buffalo Springs, two clearly defined divisions may be seen, which are of different age. The long bar projecting into the valley and marked with the numbers 95 to 100— indicating depth of water in feet at the highest stage of the former lake—is of older date than the group of v-shaped structures at a higher level. The main embankment has a broad, smooth top, which is covered in places with lithoid and dendritic tufa, and is partially coated, especially on the sides, with fine lacustral sediments. Below the point marked with the figures 190, there is a steep scarp nearly a hundred feet high, from the base of which the bar continues on in the same direction as at the higher levels, but is more deeply covered with sediments, and finally becomes so com- pletely inclosed that its presence is only indicated by the rise of the lacus- tral beds as they arch over the buried structure. The main embankment is thus older than the stages of the lake during which lithoid and dendritic tufa was precipitated, and was formed previous to a high-water period, during which the lacustral beds covering the structure were deposited. Considering next the group of y-shaped bars at the north of the main structure, we find that the base of this compound group, so far as is revealed by the topography, is older than the highest portion of the main embank- ment, which was built upon it. The structures that occur from the Lahon- tan beach down to a horizon 75 feet below that level are of later date than the bar which is prolonged into the valley, as is shown by their freedom from both lacustral sediments and tufa deposits. The difference in age of the two main divisions of this group thus fur- nishes evidence similar to that presented at the Buffalo Springs locality. The higher structures in each case are the younger. These two groups are the complement of each other, however, in the fact that the one at Buffalo Springs was built principally by currents from the north, while the second U. 8. GEOLOGICAL SURVEY LAKE LAHONTAN PL. XXI BT, Lt, _ ARs LM jrmalt ee “4, p me, We FF Sar i ls el Ve ry i, he fiona LS iphin a i r set Li ‘ fie alli Lieto : : eet EM Dees olin t Al Se a (9) Ue $7 h i ay Re 7 & DUS Ahk " VL j ys ore | ee : : ‘i ae és an i deed le Sesane zi Ee! ARABS, ae SN le! S40 Fecr ONE MILE* W. D. Johnson, Topographer. I. O. Russell, Geologist. GRAVEL EMBANKNVENTS THREE MILES SOUTH OF BUFFALO SPRINGS, NEVADA EMBANKMENTS NEAR BUFFALO SPRINGS. 119 group, three miles south along the same shore, was constructed almost entirely by currents from the south. The manner in which a gravel structure once started on the margin of a lake continues to induce deposition in case the waters rise, is well illus- trated by the group of bars at the right on Plate XXI, which is literally a pile of y-bars, the lowest in the series being the oldest. The thickness of gravel in this compound structure exceeds a hundred feet, and, as shown by the topography, the material composing it was nearly all brought from the south. Besides the embankments that have been specially examined, there are many others in the Lahontan basin of equal magnitude and perhaps equally instructive, which illustrate the variety of topographic forms produced by the action of waves and currents. On the east shore of Walker Lake are two localities where gravel em- bankments of large size have been built out from the old lake shore and form capes the ends of which are washed by the waves of the present lake. These may be distinguished on Plate XV by the manner in which the rail- road curves about them, close to the water’s edge. At each of the localities there are a number of y-shaped gravel deposits that have been built one above another from a common base, so as to produce an exceedingly com- plicated structure. . In Alkali Valley, about three miles west of Sand Spring Pass, is another locality where the gravel accumulated along the shores of the former lake may be studied to advantage. Other deposits of the same character may be seen on the east side of Humboldt Valley, between Rye Patch and Humboldt House, and again at the south end of Winnemucca Lake. A plat of the gravel structure at the last named locality is given below, which will serve as an illustration of the manner in which an embankment of large size may be thrown across a narrow strait so as to obstruct the drainage when the waters retire. The deposits at this locality are very similar to the embankment at the west end of Humboldt Lake, represented on Plate XVIII, and find a par- allel in the Bonneville basin in the immense bar at Stockton, Utah. In the 120 GEOLOGICAL HISTORY OF LAKE LAHONTAN. instance before us, the gravel forming the embankment was brought by shore currents from the north, along the east side of Winnemucca Valley, and deposited, when the current was deflected from the shore, so as to build the structure still remaining. This is a remarkably uniform embankment, tnt TERED Nigh RT i Ws. aa \\,4re li \ ys ant K Te z Zz z KN At AA Nit lary aa Fic. 19.—Gravel embankment at south end of Winnemucca Lake, Nevada, about 250 feet high, which has all the features of an artificial structure in- tended to dam the valley of Winnemucca Lake. Its western end does not reach quite to the west shore of the strait, and since recession of the waters in which it was formed it has been truncated by the erosion of the branch of the Truckee River which flows into Winnemucca Lake. Medial gravels. 7. Sandy loam, massive ; to river ....-..--.-.-.-..-.. 3 33 A double fault-line extends through the series, as shown on Plate XXIII. A similar double fault occurs 300 feet northward of the first, in the same vertical cliff (see Fig. 26, page 165), but the throw is in the opposite direc- tion, showing that the whole included block, 300 feet long, has been bodily depressed 2 or 3 feet. The marly clays forming the upper portion of the section are, as usual, markedly unconformable to the gravels underlying them. In making the drawings of detailed sections represented on Plate XXIII, the entire vertical range of the exposures observed was not represented. Mon. xI--——9 150 GEOLOGICAL HISTORY OF LAKE LAHONTAN. Section B.—West bank of Humboldt River, 4 mile above Oreana. Feet. 1. Marly clay, light colored} sanders 2-1 ose ee sme > == leo el aia ale 30 2. Marly clay, yellowish, fine-grained, laminated..-..........--..------------ 4 3. Marly clay, light colored, sandy, like No. 1.-..........-.-..---...--------- 4 AN Grayol-cross-bedesterrup nous. eaels a= eine oe eae ee ee ee eae 1 5. Marly clay, drab-colored .......-----.----- asec bho coco dsopossorecsceoces 1 6. Gravel, eross-bedded, ferruginous .--.....-... -----.----------------------- 1 7. Marly clay, finely laminated, jointed .----....--..-..-----.-.-..--. Beene 5 8. Marly clay, more sandy than No. 7, thick-bedded ; e PUVOD se 3 ecco eeteee rae 15 61 The exposures in this portion of the canon walls vary greatly as one follows them up or down stream. ‘The middle member especially changes in both the character of the strata and their inclination. Section C.—/Vest bank of Humboldt River, 24 miles above Oreana. Feet il, Sotrmovelenvel fin os S5 So cace Se oso oses odes cade caes 12 2. Marly clays, white, laminated -.-...-.-.-..--.--.-- 12) 3= Marly clays, brownish, loams-..-..----..---.--..--. 10 Wig es eee sme aI JO hyp ERE UAT) 96 case cemo soe soo seosSsSeSe S50 25 J 5. Gravel and sand, cross-stratified ......--..--------. 25 Medial gravels. 6. Marly clays and loam; to river.......-.. .----. ---- 10 Lower lacustral clays 94 Section F.— West bank of Humboldt River, at Rye Patch. Feet. 1. Molian sand and alluvial gravel, variable..-. 1 ie : 2. Loam, sandy, light-colored, fine ..---..---.-- 3. “Tufa mushrooms” (dendritic tufa)-..---.---- | 4. Ostracoid and gasteropod shells ...--..------ Upper lacustral olays. 5. Sand, loamy, buff-colored, with small concre- | WOOP MPAA TINS Seo on ooas poosed Ssecau se 16 6. Gravel, rounded, cross-stratified -:..--...---. 18.5) % Marl Sibufi-colorediseessr ss] eee ae see 6 8. Gravel, cross-stratified .-----..---..----..--- 9 9. Loam, with some cross-bedded gravel .-.-. -.-. et 10. Gravel, cross-stratified ............-.-....-.- 3 11. Sand, cemented by carbonate of lime -... ---- 0.4 > Medial gravels. 12. Loam, fine, cross-stratified ...-..--.--------- 2 13. Sand, white, marly (much thicker in east ' WTO CRYO MN) Seo hoon dense po aonaceasageass 4 | 14. Loam, with irregular strata of gravel--.----- 40 | 1bniGravelcementedececesestece costes eee eee es) 16. Loam and fine gravel; to river..---..-----.- 75 Lower lacustral clays. 196 to 201 The separation of the three members is more difficult to trace in this locality than is usual; the above divisions are somewhat arbitrary. SECTIONS EXPOSED IN HUMBOLDT CANON. ok: Section H.—North bank of Humboldt River, 6 miles below Mill City. Feet. 1. Aolian sands, withsome gravel, irregular in thick- 2. Marly clay, white, regularly laminated, jointed.... 15 Upper lacustral clays. 3. Loam, sand, and gravel, massive medially, cross- , ‘ stratified above and below..---..----..---------. 12 HOUTEN 4. Marls, regularly laminated, light drab; to river... 10 Lower lacustral clays. “37 The medial gravels are markedly unconformable by erosion to both the upper and lower lacustral beds. Section L.—South bank of Humboldt River, Mill City. Feet. 1. Weathered marl, zolian sand at summit.......--- 2.5 2. Marly clays, obscurely stratified, gray-.-----.----- 3.0 3. Marly clays, white, laminated.......--.---.-----. 3. 0| 4. Marly clays, sandy, brownish, obscurely cross- pigs lacustral clays. SANG |= S655 needs sooSee coe Ode eSGeas Hoes Hace 2.5 5. Marly clay, white, laminated, jointed....-....--- 9.0) 6. Sand and gravel, somewhat ferruginous, fossilif- GH sc ca nngcomasae ceoe cdesas Huon beecaesacoanEn 0.5 7. Sand, gravel, and pebbles, cross-stratified ....-... 5.0 8. Sand and loam, massive, with pebbles....-..----. 5.0 } Medial gravels. 9. Sand and loam, obscurely andirregularly stratified. 4. 0 10. Sand and gravel, with ferruginous current.-...-.-- 0.3 11. Sand, cross-stratified, fine... ......-..........-.- 3.0) 12. Marly clays, regularly laminated, ash colored, }Lower lacustral clays. jeinted, with some tufa at summit; to river ---. 3.0 40.8 The tufa in the lower lake-beds occurs in uniform lenticular nodules, in places forming a continuous layer an inch or two thick. Dendritic tufa, in the form of mushrooms, occurs in the upper Jake-beds above No. 5, near where this section was taken. EXPOSURES IN THE CANON OF THE TRUCKEE. The sedimentary deposits accumulated in Lake Lahontan are also well exposed in its precipitous banks of the Truckee River from the point where it enters the basin of the former lake, about 15 miles westward of Wads- worth, to its termini in Pyramid and Winnemucea lakes. Above Wads- worth the exposures are entirely of upper lacustral clays, which occur in fragmentary masses on the sides of the canon in places where they have ily GEOLOGICAL HISTORY OF LAKE LAHONTAN. been sheltered from erosion. The western bank of the Truckee just below Wadsworth, and 2 or 3 miles from the gorge through which the river enters the valley, is about a hundred feet high and exposes the following diversi- fied sections: Feet. Ie Alolian sands ¥. 525 a2 eaactoc selene eae = aioe Se ae ele ele eee ei 5 to 18 2. Sandy clay, fine, evenly stratified .-.--- .--..... ----------.-.-------- 12 3. Clay, drab-colored, fine-grained, homogeneous .-....--....----.----- 6 4, Clay, evenly stratified, ferruginous' ~-..---- ---- ~-- 5 os2---=----====-- 1.5 5. Sand, argillaceous, in contorted strata..-.---.....---.---.---------- 3 6, Sand, dine, clean; sharpen asso -cer nae seer eee eeee ee ae 2.5 7 Clay, sandy, terlucanous:)) OI LOGue cme ee eae sere econ = eae nee 2 8. Sand: coarse;and pebbl y= i." 20 a= cocoa oe tea eee as ceeye eee 5 9: Clay; argillaceous)--2-=-sescka see eke e = oan eee eee eee eee 2 LOM Sandy ferru ol OUS ese eee eee ree alee ee ee eater 10 11. Clay, drab-colored, with seams of fine sand -..--..-----.----.------ 2 125 \Sandlandoravels mica ceouspc--teseeaerssee ae es eee eee ne eee 10 13. Gravel, well rounded, with seams of sand and occasional boulders sometimes:2 deetnidiam eters sna... sae eee cee eee eaten aoe 6 14. Sand, evenly stratified, micaceous, ripple-marked ......---..-.-.---- 2 15 Sand sharp. elean ami caCeOUs | seem see esta eee ies eee 12 16. Sand, evenly stratified, micaceous, ripple-marked and current- bedded): passin oan tO eee ee sees ena eee ene eee eee 3 17. Clay, fine, evenly stratified, drab-colored, sometimes sandy; jointed by two systems of fractures nearly at right angles, and resting un- CONTOLMAD LY Wp ON — = eee aso ae ee see eee a ea 6 18. Gravel, well rounded, current-bedded, and containing boulders 2 feet ny GLEN SER Ue) Da oon seo oon posers Seenc OoSmen OsosecHaeone once 20 110 to 123 The numerous changes recorded by this section are no doubt to be accounted for by the proximity of the former mouth of the river, from which the greater part of the débris forming the beds was derived. A noticeable feature of the section is the fine exhibition of double jointing to be seen in bed No. 17. This stratum is of compact and nearly homogeneous, sandy clay, resting on a thick deposit of unconsolidated gravel and bowlders, and overlain by similar material. As the inclosing beds are too loose and incoherent to exhibit jointed structure it seems evident that the forces producing the joints must have originated in the clays themselves; for it is difficult to understand how external agencies, as an earthquake shock for example, could have been transmitted through the loose gravel deposits inclosing the clays. The jointed stratum to which we have called attention apparently represents the lower lacustral clays, but as the section is rendered abnormal by its proximity to the ancient mouth 2 ten Ce ee U 8, GEOLOGICAL SURVEY Agency ridge ( 70 ie Zacustral Maris. ZLacustral Maris with. Tuta Stratum. Horizontal W J MeGee, Del. SECTIONS CF LAHONTAN SE! Fine Lozmy Graveis. Coarse Gravels. I. OC. Russell, Geologist. ¥ TRUCKEE CANON, NEVADA t PL, XXIV ONTAN 1. O. Ruasell, Geoloyist, TRUCKEE NARROWS LAEE LA Coarse Gravels. Le ASE PSOE Fine Loamy Grave/s. ma RNa a So 1 OF LAHONTAN SEO ) SECTI ty) Nye Dacustral Maris with Tuta Stratum, U. 8 OBOLOGICAL SURVEY WJ MeGee, Det, em nnn \\\ SECTIONS EXPOSED IN TRUCKEE CANON. 133 of the Truckee River, the three divisions of Lahontan sediments so easily recognized in many localities are here indefinite. Continuing towards Pyramid Lake with our study of the exposures in the river banks, we find the section changing in its details and losing the complex character observed at Wadsworth. Beginning a mile or two below the position of the section given in detail above, and continuing for four or five miles down the river, the exposures are almost entirely of upper lacus- tral clays, including a few irregular strata of current-borne material. This is indicated by the following section observed on the west side of the river about four miles below Wadsworth: Feet. 1p REMC Gh poSenbae a sou onbosoe sane Socuaucans Boerner Se aeroa Saas 1 to 2 2. Dendritic tufajin: mushroom-torms| .=-)2.+--25s5-22-0 e252 222 eee 1to1.5 Ses lavantine tan ven ONnUOINOUSNoa=ser Ee om asset coe eee oe ene ee 4 a Clay, compact, .drab-colored 2 a2 sess seees a= sean ee iseccesssoees 12 Oomsand, fine;sripple=markediese soe eae eee aes ee eee ee feos 1 Ga Clay ine sevenlyistrautied «seme canoe ee ee eee eeee = see esaeace 2 jo sand- andleravel, Gurrent-~beddedis-en oa24--— ses esccees eae See 1 Sie Clays fdrab-cOlored ges sao ats tears ee mera eerie cae ace ke 8 Qassandsenipp lem ance direc. Ses ses ae oie ee Ne ed So 1 10. Clay, evenly stratified, with some sandy layers; to river.....-..- 100 Near the locality where this section was observed, but on the opposite side of the stream, the lower fifty feet of the canon wall are composed of coarse gravel which evidently represents the middle member of the Lahon- tan series; half a mile down stream, however, the entire section is again composed of lacustral clays. Other abrupt changes of this nature are common and seem to indicate that the medial gravels occupy an old eroded channel in the lower clays, which is crossed irregularly by the present stream channel. Continuing down stream, one finds good exposures of the upper clays resting on coarse current-bedded gravels which are without question a por- tion of the middle member of the series. The medial gravels are here probably represented in part by a heavy deposit of reddish-brown débris, somewhat coarser than the normal lacustral clays and having a close resem- blance to the upper or flood-plain portion of the medial gravels observed in the Humboldt section. On the east side of the river this deposit becomes thinner as we follow it westward, and at length disappears in a thin wedge, 134 GEOLOGICAL HISTORY OF LAKK LAHONTAN. at the same time increasing in thickness in the west bank of the cafon, until it finally composes the entire section of more than a hundred feet. Just before the Truckee Canon opens out into the valley occupied by Pyramid and Winnemucca lakes, it becomes quite narrow, and is bounded on either side by rocky walls; for convenience of reference we have called this the “Truckee Narrows.” From this point to the Agency Bridge, a distance of about four and a half miles, the walls of the canon exhibit a continuous section in which the tripartite character of the Lahontan sedi- ments is strikingly displayed. The exposures actually observed on the east side of the stream have been sketched by Mr. McGee and form Plate XXIV. The most instructive feature illustrated by this section, as is the case of the exposures along the Humboldt, is the fact that it consists of two series of fine homogeneous strata, separated by a heavy deposit of heterogeneous, current-bedded gravels. A generalized section of the beds here exposed agrees in a remarkable way with the similar sections observed in the Hum- boldt Caton. The upper and lower lacustral clays occurring in the Truckee section, like those exposed in the banks of the Humboldt, show but little variation. They are composed of fine, evenly laminated, drab-colored, marly clays, that are somewhat saline and alkaline as indicated by chemical tests. On the west side of the river near the Agency Bridge, however, the upper clays show some variation, especially near their contact with the underlying gravels, as is exhibited with considerable detail in the section forming Plate XXV. One of the most instructive portions of the Truckee section is a stratum of dendritic tufa interbedded with the upper clays. At the northern end of the section, 7. e., towards the deeper portion of the lake in which the sedi- ments of tufa were deposited, the tufa-stratum is but 3 inches thick and is buried beneath 25 or 30 feet of laminated clay ; when followed shoreward, or up stream in reference to the present drainage, the tufa gradually increases in thickness, at the same time approaching nearer the surface of the section, ~ until at the Narrows of the Truckee it forms a sheet of huge mushroom-shaped masses at the top of the bank, which are from 10 to 15 feet in diameter and so thickly planted that they form a continuous pavement fully 10 feet thick. The rocks at the Narrows above the level of the lacustrine deposits are U. 8. GEOLOGICAL B8URVEY LAKE LAHONTAN PL, XEV EV AWA AWARE ANIOE pe ee ee =< = Lacustral Mar]. Z % g vmous Loar.” OLscourety stratified Sand ani Gravel. > 7 p oes Fe ee Horizontal and Vertical Scale. Feot. WJ McGee, Del. TC. Russell, Geologist. SECTION OF LAHONTAN SEDIMENTS NEAR AGENCY BRIDGE, TRUCKEE CANON, NEAVDA. \\ SECTIONS EXPOSED IN TRUCKEE CANON. 135 coated with a continuation of the same tufa sheet, the upper limit of which is about 200 feet below the highest of the ancient water-lines engraved on the sides of the valley. The tufa interstratified with the upper clays almost invariably starts from small nuclei, and, forming dendritic branches, spreads out above into dome or mushroom-shaped growths ; in some instan- ces the tufa is prolonged downward below the general level of the stratum to which it belongs, and forms irregular vase-shaped masses below the con- tinuous tufa layer. Immediately below the tufa, and sometimes adhering to it, are great quantities of Cypris and gasteropod shells, and occasionally bones of fishes, indicating that the waters from which the calcium carbonate forming the tufa was precipitated were far from being concentrated saline solutions. Throughout the section, the contact of the media! gravels with both the underlying and the overlying clays is uncontormable, owing, in each case, to the erosion of the lower member, as is well shown in Figs. A, C, and D, Plate XXVI, which are accurate sketches of observed exposures, and illus- trate the filling of channels, formed principally by erosion, with current- bedded gravel. The lacustral clays forming the lower portion of the section are, in places, exposed to the depth of 100 feet, but what their total thickness may be it is not possible to determine from the present exposures. When exam- ined at some distance from the shore of the basin, they exhibit little varia- tion, and are normally finely laminated, marly clays An exception is found, however, a short distance above the Agency Bridge, on the east side of the river, where a rounded boulder of hard volcanic rock from 2% to 3 feet in diameter occurs several feet below the top of the lower clays. This is a much larger block than any seen in the medial gravels, and evidently must have been floated to its present position, probably through the agency of ice. Although rounded and worn it did not exhibit striations or planed sur- faces, and gave no proof that it had ever been subject to glacial action. In places, the lower clays exhibit contortions which in some instances can only be accounted for by a movement of the beds since their deposition, caused apparently to the weight of the superimposed masses of gravel and clay. In other exposures the contortions and convolutions of the laminated 136 GEOLOGICAL HISTORY OF LAKE LAHONTAN. deposits are apparently due to their having been formed in agitated waters ; just how the intricate folds and contortions were produced, however, it is extremely difficult to explain. In a few localities the lacustral clays, especially below the medial eravels, are faulted; and at times the strata on one side of a fault have been thrust over the beds forming the opposite wall, as indicated at the left on Plate XXV. In this instance the projecting strata seem to have been removed by erosion previous to the deposition of the superimposed clays. The medial gravels in the Truckee section vary from 25 to 100 feet in thickness, and exhibit great diversity both in composition and structure, thus indicating many variations in their mode of formation. Examples of cross-bedding are abundant, and the presence of arched strata and lines of unconformability, as well as the irregularity of the beds and the manner in which they wedge-out and are replaced by others of a somewhat different nature, all tend to show that the entire middle member of the Lahontan series here exposed was deposited in shallow, current-swept waters. The arches seen in the canon walls are, apparently, cross-sections of current- built embankments, while the irregular layers of fine sediment are proof, on the other hand, of more quiet condition during which the fine silt held in suspension was allowed to subside. The general conclusion that the medial gravels were formed during a time of low water, separating two periods when the lake was broad and deep, cannot be questioned by any one who has examined the records exposed in the Truckee section, which, as previously stated, are in harmony with the similar evidence furnished elsewhere in the basin of the ancient lake. On following the Truckee River from the Agency Bridge to its mouth, one finds its banks becoming low, and exposing, for the most part, only por- tions of the upper clays; in a few localities, however, limited sections of the medial gravels may be seen, thus showing that the valley could not have held a lake much, if any, larger than that of the present day during the time that the medial member of the Lahontan series was being deposited. ay ~ Eolian sand. + Fine, well-worn gravel. ------- Evenly stratified clay, contorted in places, -~ Dendritic tufa. -- Evenly stratified coarse clay, with odlitic grains. Granular limonite, with shells and fish-bones. —— Fine, evenly stratified, light-colored clay, ripple-marked in places. Sandy clay, compact. <"« Nearly pure Cypris shells. Light drab jointed clay, with few Cypris shells ht-drab clay, rich in Cypris shells. enly strat 1 sandy clay, with a few gravel-grains. <7 ~~ Nearly pure Cypris shells. Sse 2o+ Impure voleanic dust. “s™ Pure white voleanic dust. “s Fine sand, with Cypris shells and fish-bones. . ** Well-worn stratified gravel, cemented. een Homogeneous sandy clay. - Fine sand and Cypris shells, ripple-marked, with fish-bones. Fine gravel. Homogeneous drab clay SD 7+ Sand aud pebbles. “S™ Fine drab, jointed cluy Ss Yellowish sand ---=—. Fine water-worn gravel, cemented in places. | —=-—-— Homogeneous, evenly stratified, jointed gray sandy lake-beds, contorted tow ird base. j---—— Truckee River. BRIDGE, TRUCKEE RIVER, >t i Ace i t : wv aM ' a. . ; 2 nett ad pinta ste BO OE a ah Te te wht tte ne nena : Ps r We. SH aes f ' - * 4 : ’ 7 4 Pes } % i ; r . Pe ’ ya eu a ee eR eed te | _¥ CHURCHILL VALLEY. 137 EXPOSURES IN THE CANON OF THE CARSON RIVER. During the highest stages of Lake Lahontan its waters extended up the Carson River Valley as far as Dayton, and occupied it long enough to allow large quantities of lacustral beds to accumulate. When the lake evaporated and the river regained its ancient channel, these beds were deeply dissected by erosion. The remnants of Lahontan sediments to be seen in the valley belong mostly to the upper lacustral clays, but in places they were observed to rest on gravel deposits. The sections obtained, however, were imperfect and far less satisfactory and instructive than those described in the preceding pages. The lacustral beds exposed along the banks of the Carson, and flooring Churchill Valley, are fine, light-colored marly-clays, similar in all respects to the corresponding beds observed at many localities throughout the Lahontan basin. Interstratified with these sediments is a deposit of dendritic tufa, sometimes 3 or 4 feet in thickness, which is well exposed in the narrow channel connecting Churchill Valley with the Car- son Desert. This deposit corresponds both in structure and position to the interstratified tufa-layer observed in the Humboldt and Truckee canons. So far as known, the lacustral beds observed along the Carson River are undisturbed by post-Lahontan movement, and have nowhere been dis- sected sufficiently deep to lay open the sediments accumulated during the first rise of the lake. The Carson River rises on the eastern slope of the Sierra Nevada and flows northward through Carson and Eagle valleys, which are in reality a single basin, and enters a deep and all but impassable canon, through which it flows with a rapid descent as far as Dayton. It then enters a valley 2 or 3 miles broad—once an arm of Lake Lahontan—which contracts again to a narrow canon at its southern end. In the course of a few miles this canon again expands and forms Churchill Valley, which in its turn connects with the Carson Desert through a narrow channel now occupied by the Carson River. The contractions in the lower portion of the river channel are prob- ably due in a great measure to erosion, but are less plainly stream-carved channels than the deep gorge above Dayton. Since Lake Lahontan during its highest stages occupied the valley as far as Dayton, we are safe in con- 138 GEOLOGICAL HISTORY OF LAKE LAHONTAN. cluding that the river channel was carved in pre-Lahontan times, and also that the lake which occupied Kagle-Carson Valley must have overflowed and cut down its channel of discharge so as to drain that basin to the bottom previous to the existence of Lake Lahontan. We make this departure from our immediate subject for the purpose of showing that the sediments of the Eagle-Carson Lake, in which a variety of foot-prints have recently been discovered at the Nevada State Prison, are older than Lake Lahontan, and probably belong to early Quaternary or late Tertiary times. EXPOSURES IN THE CANON OF WALKER RIVER. The Walker River, in its course between Mason Valley and Walker Lake, flows through a comparatively narrow valley, which was deeply filled with Quaternary lake sediments and is now a desert, sage-brush-covered plain, dissected through the center by a canon eroded by the present stream since the evaporation of the former lake. Like the Humboldt, the Truckee, andthe Carson, the Walker River has exposed sections of Lahontan sediments, in which the tripartite division is well displayed. As in the former instance, the upper and lower members are fine, evenly laminated, marly-clays, which were evidently accumulated in quiet waters, and;are separated by a hetero- geneous accumulation of sand and gravel that ene an interval of low water. . The tendency of current-borne débris to accumulate in narrow straits connecting broad water-bodies has already been discussed in connection with the descriptions of the gravel deposits observed in the Humboldt and Truckee canons. A gravel embankment similar to those already described occurs a few miles northward of Walker Lake and forms the divide between Walker Lake and Walker River valleys. In this instance a large embankment was built. completely across the mouth of the narrow strait that formerly con- nected the open waters of Walker Lake and Mason valleys; subsequently this structure was cut through by waters flowing from the northward, thus revealing a section of the inclined and arched strata in which the gravels were deposited. A generalized section compiled by Mr. W J McGee, from many detailed observations, is reproduced in Fig. C, Plate XXVIII, which represents the a U. 8. GEOLOGICAL SURVEY ~ WJ MeGee, Del. Lacestral Adal. DETAILED SECTION OF LAHONTAN § DiMENTS, TRUCKEE CANON NEVADA. I. GC. Russell, Geologist. SECTIONS PXPOSED IN WALKER CANON. 139 structure of the Lahontan sediments exposed in the canon walls for a dis- tance of 18 miles. The highest point in the section is at the crest of the embankment, which crosses the valley and marks approximately the level of the highest water stage of the former lake. Between the embankment mentioned above and Walker Lake, a distance of 8 miles, the river banks vary from zero at the lake to 50 or 60 feet in the neighborhood of the em- bankment. In this interval the exposures are almost entirely of upper lacustral clays, with intercalated beds of volcanic dust, but at a few locali- ties, in the northern portion of the section, the medial gravels and under- lying clays may be seen at the base of the escarpment bordering the river. Where the stream-channel crosses the embankment, thé entire exposure, 200 feet high, is composed of inclined and arched strata of sand and gravel inclosing irregular and loamy beds. The entire series has a characteristic pinkish tint due to the presence of iron oxide. This embankment occurs unconformably between the upper and lower clays, and, like many similar structures when seen in section, exhibits anticlinals of deposition. Its base is not exposed to view, but as the clays of the lower series occur near at hand, both to the north and south, it seems probable that the gravels com- posing the embankment were, at least in part, accumulated during the time the lower clays were being deposited. Like the embankment at the south- ern end of Humboldt Lake, this structure was probably begun early in the history of Lake Lahontan, and has been enlarged many times since. The last addition was contemporaneous with the deposition of the upper clays, or perhaps in part subsequent to it; in the main, however, it is composed of the medial gravels of the Lahontan series. Northward from the crest of the embankment the cation walls decrease in height, as represented in Fig. C, Plate XXVIII, all the way to Mason Valley, where the river becomes a surface stream. The medial gravels are exposed for about 8 miles north of the embankment, and appear again at a point where they have suffered some local disturbance about 4 miles below the point where the river leaves Mason Valley. Throughout the entire exposure of lower lacustral clays observed in the Walker River Cation, the strata are of light-colored, laminated, marly clays, of the same nature as the corresponding beds occurring in the Hum- 140 GEOLOGICAL HISTORY OF LAKE LAHONTAN. boldt and the Truckee canons, and therefore do not require farther description. The medial gravels, in common with lacustrine shore deposits in general, are heterogeneous accumulations of worn and rounded sand, gravel, and boulders, with occasional inclusions of finer débris ; cross stratification pre- vails, and many of the beds were deposited in an inclined position. The upper lacustral clays in the Walker River section are more varied and indicate more complex conditions of deposition than the similar expos- ures that have been described in the preceding pages. The upper and lower portions of the upper clays have the normal features of the deposit, but an intermediate portion, varying 20 to 30 feet in thickness, is of a more diversified character, and includes strata of sand and gravel which are fre- quently iron-stained and in many places form contorted and folded layers. This portion of the upper clays obtained the name of the ‘“bone-bed” in our field notes, from the numerous mammalian remains that it contains (see Chapter VI). It is exceptional in the Lahontan series, and evidently must have been formed under peculiar conditions. The only hypothesis which seems to furnish assistance in interpreting the phenomena observed assumes that the embankment dividing Walker River and Walker Lake valleys formed a dam in late Lahontan times that obstructed the free cir- culation of the waters occupying the two basins and caused the region above the obstructions to become a swamp or a shallow lake in which the iron-stained deposits of varying character containing mammalian remains were accumulated. Afterwards the lake rose sufficiently to flood the valley and allow homogeneous, fine-grained clays to accumulate. In this portion of the deposit the shells of Margaritana margaritifera ave abundant. The surface of the upper clays over large areas both in Walker Lake and Walker River valleys is coated with an abundance of dendritic tufa, which occurs both in mushroom-shaped masses that have formed about small nuclei and in irregular vertical sheets which penetrate the clays and in some instances inclose considerable areas. These sheets of tufa seem to have formed on the sides of fissures, or perhaps on eroded surfaces which had been submerged, in such a manner as to take an accurate cast of the beds against which they were deposited. The upper clays in the Walker River section correspond not only in their composition and arrangement “heed, U. 8. GEOLOGICAL SURVEY LAKE LAHONTAN PL. XXVIII : a —— = S o = — = = SS 10 } 30 40 so Mari Sandy Marl, Marl with Bone-bed. Sax@ and Gravel 3 — WJ MeGee, Del. T. C. Russell, Geologist. SECTIONS OF LAHONTAN SEDIMENTS IN WALKER RIVER CANON NEVADA. erp eens ed ee Fhe er ee at ee . SECTIONS EXPOSED IN WALKER CANON. 141 with the similar beds in other parts of the Lahontan basin, but they contain the same species of fossils. Their tufa deposits in various parts of the old lake basin record similar chemical conditions. The following section observed in the left bank of the Walker River, about two miles above the gravel embankment shown on Plate XXVIII, represents the prevailing character of the exposures to be seen in this re- gion: Feet. Aiolian deposits forming desert surface ....-...-. 1 to 10 Light-colored marly clays, passing into ferrugi- Upper lacustralclays..3 nous sandy beds, sometimes contorted, contain- | ing detached mammalian bones; changing to ( marly clays at the base.-.-...--.-...-----.---. 40 to 50 Contact unconformable. Medial gravels....-.----- Gravels and loam, colored with iron -..-..-.------ 25 to 30 Contact unconformable. Lower lacustral clays -..Light-colored marly clay; to river .....-..-.---- 75 The sections taken at various points along the Walker River show great variation, but the differences are caused almost entirely by the want of constancy in the medial gravels; the upper and lower members of the series are remarkably uniform throughout. In the majority of cases where the upper or lower contacts of the medial gravels could be seen they were found to be unconformable with the adjacent beds. The most difficult problems presented by the superficial geology of the Walker River Valley are in connection with the orographie disturb- ances that have affected the region in post-Lahonta ntimes. The valleys occupied by Walker Lake and Walker River are of the Great Basin type, and owe their formation to pre-Lahontan faulting; the main displacement that gave origin to the depressions—which are structurally a single basin— follows its western border and determines the extremely precipitous eastern face of the Walker Lake or Wassuck Mountains. Other faults, less plainly distinguishable, occur on the eastern border of the valley, especially near its northern end, and connect with the displacements to be seen in Mason Valley. Some of these ancient fault lines, including the largest of all—that following the western border of the valley—appear at the surface within the basin of the former lake; in such instances a post-Lahontan movement of the ancient 142 GEOLOGICAL HISTORY OF LAKE LAHONTAN. displacements is usually indicated by fresh scarps in lacustral clays and gravels. Since the desiccation of Lake Lahontan there has been consider- able movement along some of these ancient lines of fracture, and the La- hontan beaches and terraces no longer retain their normal position, but in places have been carried far above the horizon which they originally occupied. If we consider the crest of the gravel embankment separating Walker Lake Valley from the valley occupied by Walker River as approximately the original level of the Lahontan beach, we find that the eastern end of the structure, as determined by Mr. McGee, is now fully 200 feet above its original position, as indicated at x’, Plate XXVIII. The only explanation of this phenomenon the writer can offer is that the fault following the eastern border of the valley has increased its displacement in post-Lahontan times and carried the shoreward portion of the bar above its normal position. Similar disturbances may be seen in the northern part of the same valley, where a post-Lahontan fault occurs on each side of the basin exposing char- acteristic sections of Lahontan sediments. The altitude of the beach on the eastern side of the valley is indicated at x, Plate XXVIII. In the bot- tom of the valley and near the northern end, the strata are arched as indi- cated in the generalized section. From the limited section open to exami- nation, this seems to be a variable anticlinal, and, if so, it is the only post- Lahontan arch of this nature that has been observed. The movements that produced the disturbances in the northern part of the Walker River Valley are connected with the recent displacements to be seen in the vicin- ity of the hot springs in Mason Valley, and are so indicated on Plate XLIV. Local faults affecting the Lahontan sediments are of frequent occur- rence, especially in the lower portion of the Walker River Valley; the throw of these displacements is seldom over 40 or 50 feet, and they have caused but little change in the topography of the valley. They are of different dates, as is illustrated by figures A and B, Plate XXVIII; in the former, the dis- placement took place previous to the deposition of the medial gravels; and in the latter, after the upper clays had been deposited. We have described the orographic movements in this region in some- what general terms, for the reason that it is difficult to describe the facts on a | GENERALIZED SECTION. 143 which our conclusions rest with as much accuracy as could be desired, and also because the subject will claim further attention in connection with other orographic disturbances that have affected the Lahontan basin. GENERALIZED SECTION OF LAHONTAN SEDIMENTS. On grouping the numerous sections of Lahontan sediments observed in the Humboldt, Truckee, Carson, and Walker canons, we have the fol- lowing generalized section of sedimentary deposits formed in the ancient lake: Average thickness, in feet. [Uover lacustral clays: Evenly laminated marly clays, fine and homogeneous, usually saline; with interstratified bands of dendritic tufa near the top; in places containing intercalated layers of vol- canie dust. In some places this member is divisible into three parts, the upper and lower being normal clays, while the intermediate member is more sandy, and usually contains iron-stained lyse, that are frequently contorted -...........-.....-...---.-. 50to075 Fossils: Cypris, Anodonta, Margaritana, Spherium, Pisidium, Floren, Gyraulus, ete., together with mastodon or elephant, horse, and camel. Contact uncomformable. Medial gravels: Cross-stratifled sand, gravel, and loam, in beds that are irregular both in thickness and inclination, frequently forming arches of deposition. At times exhibiting two plainly marked divisions; the upper being a compact, earthy, homogeneous, flood-plain de- posit ; the lower clean, well-rounded sand and gravel, at times strongly cross-bedded.. 50 to 200 Fossils: Anodonta, Gyraulus, Lymnophysa, Pompholyx. Contact unconformable. Lower lacustral clays: Laminated marly clays, very similar to the clays at the summit of the section. ‘The clays throughout the section frequently exhibit two systems of joints at nearly right angles toeach other (full thickness not exposed)... -~ =... .-2 2225-2. cic sone wen e eens oo ee eee 100 Fossils: Pompholyz. The interpretation of this section gives an outline of the later Quater- nary history of the Lahontan basin; but as the base of the lower clays is nowhere exposed, all the changes that may be recorded by the lower strata remain unknown. From the sedimentary deposits observed we learn that there have been two high-water periods in the history of the Lahontan basin, during which fine clays were deposited. Separating these two periods was a time when the lake was low and allowed current-borne gravels to be carried far out over the previously formed lake-beds. During the second flooding the waters underwent long concentration, and at a certain period deposited a vast quantity of tufa; the lake during this stage also received 144 GEOLOGICAL HISTORY OF LAKE LAHONTAN. large quantities of pumiceous dust, which must have been thrown out by some volcano in the state of violent eruption. The second rise of the lake was followed by the present period of desiccation, which witnessed the evaporation of its waters and the exposure of its sediments to subaerial ero- sion. The rivers in flowing across the exposed lake-beds carved the deep channels we have described, and are now spreading stream and current borne gravels far out in the central portions of the valleys, thus in many ways repeating the conditions that characterized the time during which the medial gravels were deposited. In order to represent the sediments of Lake Lahontan on a geological map of the region one has but to color the area once occupied by the lake with the appropriate tint. The older rocks throughout the area are not com- pletely concealed by the sediments of the lake, however, the exceptions oceurring along the borders of the basin and about isolated buttes; but these portions being usually precipitous, the belt left unconcealed is so narrow that it would be scarcely possible to represent it on a geological map of the scales ordinarily used. To prevent confusion it seems appropriate to indicate at this time some discrepancies that exist between the published reports of the United States Geological Exploration of the Fortieth Parallel and the conclusions pre- sented in the present volume. On map V of the atlas issued for that explo- ration a large portion of Lahontan basin is included. ‘The area covered by the sediments of Lake Lahontan, as determined by the present survey, are there indicated in four different ways. Some portions are represented as Truckee Miocene, others as Humboldt Pliocene, while the greater part is divided between Upper and Lower Quaternary. The areas colored as Truckee Miocene are situated at the lower end of Humboldt Lake and at the southern end of Winnemucca Lake. ‘The de- posits at these localities are similar, consisting, if the writer’s determinations are correct, of gravels that were accumulated in the form of bars or embank- ments through the action of the currents of the Quaternary lake. The some deposits about the south shore of Humboldt Lake have been described at length in the preceding pages (105 to 112), and a detailed map of the area DISCREPANCIES IN CLASSIFICATION, 145 presented on Plate XVIII. The embankments near the south end of Win- nemucca Lake are described on page 120. The discrepancy in reference to the nature of the gravel deposits bordering Humboldt Lake may be seen by comparing the pages referred to above with the description given on page 742 of Vol. II of the reports of the United States Geological Explo- ration of the Fortieth Parallel. The entire area represented as Humboldt Pliocene, on map V of the atlas cited, has been considered throughout the present volume as of Quaternary age, and as furnishing the most typical exposures of Lahon- tan sediments, as will be seen by referring to the descriptions of the Hum- boldt and Truckee canons. The areas colored as Lower Quaternary on map V, of the atlas named, are mostly playa-deposits; while the areas designated as Upper Quaternary are largely covered with alluvial gravel, especially near the mountains, but in the broader valleys within the Lahontan area large portions thus designated are floored with Lahontan sediments. In the present report Upper and Lower Lahontan clays have been recognized; these might with propriety be termed Upper and Lower Quaternary, but cannot be correlated with the Upper and Lower Quaternary of King. The exposures of upper and lower Lahontan sediments are so limited, occurring mostly in canon walls, that they could scarcely be represented on a map of the scale used in that atlas, and if mapped they would not agree with the classification of the Quaternary there used. As the facts are interpreted by the present writer, the lake beds'there mapped as Lower Quaternary belong to Upper Quaternary, while the playas also mapped as Lower Quaternary are recent. The alluvial deposits, there mapped as Upper Quaternary, are deep forma- tions whose accumulation began at least as early as the Tertiary and has been continued to the present time. Their surface layers are in part mod- ern, but other areas have received no recent additions and are superficially Upper Quaternary. Mon. x1——10 146 GEOLOGICAL HISTORY OF LAKE LAHUNTAN EXCEPTIONAL SEDIMENTARY DEPOSITS. PUMICEOUS DUST. In describing the section of upper lacustral clays observed in the Humboldt, Truckee, and Walker River canons, strata of fine silicious material, varying in thickness from a fraction of an inch to five or six feet, were noted at a number of localities; it is now our intention to describe these abnormal deposits more fully. In all the exposures of this material the same characteristics were observed. The beds are composed of a white, unconsolidated, dust-like, silicious substance, homogeneous in composition, and having all the general appearance of pure, diatomaceous earth. When examined under the mi- croscope, however, it is found to be composed of small, angular glassy flakes, of a uniform character, transparent and without color, but sometimes traversed by elongated cavities. When examined with polarized light, it is seen to be almost wholly composed of fragments of glass, with scarcely a DS ~~ EO ES we Fi Aye at re = ah a Ke 1. Volcanic dust which fell in Norway, March 29 and 30, 1875, 2. Volcanic dust emptied from Krakatoa, August 27, 1883. 3. Voleanic dust from the Truckee River, Nevada. Quaternary. 4. Volcanic dust from Brakleast-Hill in Saugus, Mass., pre-Carboniferous. Fic. 23.-—-Voleanic dust. trace of crystal or of foreign matter. On comparison with volcanic dust that fell in Norway in 1875, derived from an eruption in Iceland, with the dust erupted in Java in 1864, and the similar material ejected in such quantities from Krakatoa in 1883, it is found to have the same physical characteristics; but it is much more homogeneous, and, unlike the greater part of the recent dust examined, is composed of colorless instead of brown or smoky glass. In the following figure, which we copy from STRATA OF VOLCANIC DUST. 147 Mr. J. S. Diller’s instructive article on the volcanic sand which fell at Unalaska, October 20, 1883,” the microscopic appearance of volcanic dust, from various localities and of widely different geologic age, is shown with accuracy. The peculiar concave edges and acute points of the shards of glass render it evident that they were formed by the violent explosion of the vesicles produced by the steam generated in the viscid magma from which the glass was formed, and were not produced by the mere attrition of the fragments during the process of eruption. It is noteworthy that the dust erupted from Krakatoa but yesterday is undistinguishable in its main characteristics from the material of a similar origin which fell in the waters of Lake Lahontan during the Quaternary, or from the dust thrown out by some unknown and long since extinct volcano in the vicinity of the Atlantic coast, which fell near the site of Boston during pre-Carboniferous or pos- sibly in pre-Cambrian time. The volcanic phenomena of to-day are gov- erned by the same laws as obtained at the dawn of geologic history. Farther study revealed that even the finest of the dust obtained from the basin of Lake Lahontan has identically the same physical properties as pumiceous rhyolite forming the Mono Craters, ground in a mortar to a cor- responding fineness; under the microscope the two powders were very similar. The dust deposits are rich in silica, as shown by the following analysis, by Dr. T. M. Chatard, of a sample collected in the bank of the Truckee River near Pyramid Lake; for comparison we give also an analysis, by the same chemist, of a specimen of pumiceous rhyolite from the Mono Craters: Constituents, etc. Me eae Loss by ignition (water).........-...--. 3. 91 2. 20 SCE U OS ocnkpo cana sopososenbensaro ses 71.15 74.05 Alumina (AloOz) and iron (Fe20s) ------- | 15. 95 13. 85 Tame (CAO) seeaaeres eaten ee te ee. 0. 85 0. 90 Magnesia (MgO)....--.--....-..----.--- 0.41 | 0. 07 Magnesia (MnO).--..........--...-..... abe || socead Potash (6o@) an eee eee ea le aaa 3.36 | 4.31 Soda (Naa0) eee enene eee eee eee 4. 94 4. 60 100. 57 | 99. 98 The striking similarity in the composition of the above samples (especially when allowance is made for the greater percentage of moisture 49 Science, Vol. III, p. 652. 145 GEOLOGICAL HISTORY OF LAKE LAHONTAN. in the specimen of dust, and the fact that it has been exposed to the action of solvents much more than the rock remaining in the crater walls) strongly favors the assumption that they had a common origin. More extended operations in the field revealed that beds like those described above are not confined to the Lahontan basin, but are found as superficial deposits above the Lahontan beach at many localities and at points far distant from the old lake margins. Accumulations of the same nature occur in the Mono Lake basin, interstratified with lacustral deposits, and were also found in the canons about Bodie at a considerable elevation above the level of the Quaternary lake that formerly occupied Mono Valley. About Mono Lake these deposits are frequently of a coarser texture than those found farther northward, and, at times, graduate into strata which reveal to the eye the fact that they are composed of angular flakes of obsidian. The Mono Craters form a range some 10 or 12 miles long, which extends southeastward from the southern shore of Mono Lake, and in two instances attains an elevation of nearly 3,000 feet above the lake. A few coulées of dense, black obsidian have flowed from them, but the great mass of the cones is formed of the pumiceous obsidian which occurs both as lava-flows and ejected fragments, the latter forming a light lapilli which gives a soft gray color to the outer slopes of the craters. Fragmental material of the same nature has been widely scattered over the mountains and on the ancient moraines that occur in the Mono basin, while fine dust, unquestionably derived from the same source, may be traced to a still greater distance. From the evidence given above we conclude that the strata of fine, siliceous, dust-like material occurring in the Lahontan sections, as well as the similar beds found about Mono Lake and scattered as superficial deposits over the neighboring mountains, are all accumulations of volcanic dust, which was probaly erupted from the Mono Craters.” The greatest ‘This material could not have been erupted from the craters in which the Soda Lakes, near Ragtown, are situated, as these volcanoes are formed of quite different and more heterogeneous ma- terial. The fragments of scoria ejected from these vents are composed of basalt in which grains of olivine are conspicuous. STRATA OF WHITE MARL. 149 distance from the supposed place of eruption at which these deposits have been observed is about 200 miles. The resemblance between the volcanic dust described above and very pure diatomaceous earth is so close that it is difficult to distinguish one from the other by a cursory examination; with the aid of the microscope, however, the difference is at once apparent, as the dust seldom shows even a trace of any organism mingled with it. WHITE MARL. At a number of localities in the Lahontan basin there are exposures of white, chalky marl which does not appear in the cation sections we have described, but is exposed locally, mostly on the sides of the basin, and evidently indicates peculiar conditions of the waters in which it was accu- mulated. White marls were first observed in the Lahontan basin at the south- ern end of the desert valley, which is connected with the Carson Desert by the narrow pass in which Allen’s Springs are situated; during the higher stages of the ancient lake this valley formed a land-locked bay. That the waters did not extend through the pass at the southern end is shown by a series of barrier-bars at about the horizon of the Lahontan beach, which sweep about this portion of the ancient shore in graceful curves. These concentric gravel ridges, or barrier-bars, record a gradual recession of the waters which once filled the valley, and are especially noticeable from the neighboring hills when the slanting, afternoon light brings out their symmetric forms in bold relief. Modern drainage has cut a channel through them in a direction at right angles to their general trend, and exposed the following section: Well-worn gravel, forming barrier bars.-...-.....--.-.--.----..----.------ 15 to 25 TST Secs be, ee Seo Oe OL ae a Se 8 to 10 Finely laminated,white, chalky marl_.._..._..-- --.......:..2----..2s-- Grivel weulrennded, terri PinOus, -.o sae ase sso ee oo os aaa an Saleen lto 2 Fine sand ; to bottom of exposure ...--....--- vent psaSisceeeee seg cake ito G2 The mar! at this locality is by aneroid measurement 175 feet below the Lahontan beach, and may be traced for a hundred yards or more along the sides of the arroyo. At both its lakeward and shoreward margin it becomes 150 GEOLOGICAL HISTORY OF LAKE LAHONTAN. impure from the intermingling of sand and gravel, and finally wedges out and is replaced by water-worn debris like that forming the bars. It seems to form a lenticular mass, filling a local basin, but the section does not give complete proof that such is the case. Our observations would apply equally well to a low off-shore embankment built by gentle currents, and subsequently buried by ordinary shore-drift. The gravel bars resting on the marl were formed during a subsequent rise of the waters and were never afterwards submerged; consequently the marl must have been de- posited previous to the last high-water stage of Lake Lahontan This will be of interest when the oscillations of the lake are more fully described. Passing to other localities where white marl has been observed, we find that in sheltered ravines on the sides of the basaltic buttes overlooking the southern shore of the South Carson Lake there are fine, mealy deposits of this nature, 20 or 30 feet thick, and some distances below the highest of the Lahontan terraces, which contain gasteropod shells in abundance. Similar beds were also observed about 2 miles north of Allen’s Springs, in the bottom of the ancient channel leading to the Carson Desert. The exposure is here imperfect, and as the beds are but little elevated above the general desert-surface it is with doubt that they are referred to the same period in the history of the lake as the similar deposits observed at higher levels. White marl may also be seen at a number of indefinite exposures at a uniform horizon, some distance below the Lahontan beach, along the steep bluffs which border the Carson Desert on the south. In Alkali Valley, 2 or 3 miles west of Sand Springs, similar marls filled with gasteropod shells occur in a group of embankments that project into the valley. Another locality of the same nature was observed on the west side of Humboldt Lake at an elevation of four hundred feet above the lake surface. In the Truckee Cafion, about a mile below the Truckee Narrows, there are beds of pure, white, chalky marl not less than 50 feet in thickness, that are grouped about a butte of voleanic rock which was formerly completely buried beneath Lahontan sediments, but is now exposed by the erosion of the river. ‘These beds are in part overlain by Lahontan deposits, but the exposure is obscure and the relation of the marls to the associated clays Mi ey THE WHITE TERRACE. 151 not easily determined; no fossils were found, and it is not impossible that the marls are of much older date than the associated Quaternary beds; possibly they are of Tertiary age. The best localities of all for observing the deposits we are considering are about Pyramid Lake. In this basin they frequently appear as a con- spicuous white band along the borders of the valley at an elevation of 820 feet above the 1882 level of the lake, and form a well defined built-terrace which we have named the ‘White Terrace.” Measurements with an engi- neer’s level, as well as many observations with an aneroid barometer and hand level, show this terrace to have a nearly uniform height and to be coinci- dent in elevation with the water-line which marks the upper limit of the dendritic tufa. About the Marble Buttes, and at many points along the steep western shore of Pyramid Lake, the White Terrace is well exposed in sheltered ravines, which were coves and bays when the waters occupying the valley stood 320 feet higher than at present, but it is wanting on pro- jecting spurs. Northward of Mullen’s Gap the terrace becomes more con- tinuous, and when cut by arroyos exhibits the sequence represented in the following section : Alluvture White Marl Bs Fic. 24.—Section of White Terrace, west side of Pyramid Lake, Nevada. In some instances the outer border of the terrace has been removed so that the steep lakeward dip of the strata is not always observable. At a number of localities the terrace is from 200 to 400 yards broad, with a plane or slightly concave upper surface which usually slopes gently lakeward ; the outer scarp is steep and at times 30 or 40 feet high, but the deposit di- minishes rapidly in thickness towards the shoreward margin. The marly beds are usually underlain by alluvium, as shown in the figure, and are ay GEOLOGICAL HISTORY OF LKAE LAHONTAN. overplaced along the shoreward margin by similar material that has been swept down from the slopes above. Sometimes the marls are deeply eroded and present typical ‘bad land” topography in miniature. The White Terrace may be seen at a number of places about the north- ern end of Pyramid Lake, and in the pass leading to Honey Lake Valley. At the southern end of Smoke Creek Desert it was again observed, with its normal elevation of 320 feet above Pyramid Lake. Further northward, it occurs at a number of localities on the steep borders of the Black Rock Desert. From the numerous exposures observed it is evident that this terrace occurs all about the deeper portions of Lake Lahontan, and may be considered as co-extensive with the dendritic terrace with which it coincides in elevation. The occurrence of the marl as a shore deposit is independent of the character of the rock against which it rests; it occurs with equal pu- rity on alluvial slopes and on shores of limestone, basalt, rhyolite, ete. It is found in abundance about isolated buttes that formed small islands in the former lake, as well as along the shores of the mainland, and is therefore evidently not a product of erosion. Occasionally, however, the marl is min- gled with sand and pebbles, and when it takes the form of a free bar the proximal end will be found to contain more foreign material than the distal extremity, thus indicating the assorting power of the currents that trans- ported the material. At all the numerous localities where the White Terrace is exposed it is composed of fine, incoherent, chalky marl, which is often richly charged with the shells of fresh-water mollusks. In places the deposit is 40 or 50 feet thick, and homogeneous throughout. An analysis of a typical sample collected on the western border of Pyramid Lake Valley, as reported by Dr. T’. M. Chatard, is given below, and shows that the material is essentially an impure calcium carbonate containing a high percentage of silica : Mies EO) ase osemaeens ae aaa das ceringoradaneasenroceoso sence sochocos cbSone 3. 32 Calcium carbonate (CaCQs) .----------- -2---2 <= <-22 fone eee - = ews e ns === 64. 82 Silica(SiO;) poe s-5--- eee eee sd aa altace torte eee re eats eer por erase 22. 00 ‘Alnmina (Alb Os) assesses tee sere eee see aac SE ites) Se ote eo aera sce vas eae 5.14 Tron (Fe,03).-.-- Bae Baga Sc a eee ck oe A Sao sees shee ee Rea. See 2. 04 Tihs (CEO) ik saocestoosoceccs sone seeds cned Sar eeoncoAgsescassocnuedossades: | UGE WEY aH EY (QUEL) ei pedon sosene orsccccede decease bane aerial sec tee 1.89 100. 14 PCST-QUATERNARY DEPOSITS. 153 When examined microscopically the marl reveals a great quantity of crystallized and amorphous calcium carbonate, very similar in appearance to the same substance obtained by precipitation in the laboratory, together with other bodies which appear more clearly when the material is treaied with diluted acid. On examining the residue insoluble in acids under the microscope, is found to contain many diatoms, especially in the finer and more flocculent portion of the sediment; the coarser portion, which subsides most quickly, also contains diatoms, but is mainly composed of crystalline grains and many glassy flakes similar to those composing the volcanic dust described on page 146. The chemical and microscopical examinations render it evident that the material in question is mainly a chemical precipi- tate, but is also, in part, of mechanical and organic origin. It seems probable that the calcium carbonate forming the principal por- tion of the marl was precipitated from the waters of Lake Lahontan in a microcrystalline and amorphous form at about the time the dendritic tufa was being accumulated; and became mingled with the siliceous exuviee of the microscopic organisms that lived in abundance in the lake waters; it also received some contributions of volcanic and olian dust, but, in the main, was free from the products of ordinary stream erosion. The deposit thus formed, when near the shore, was assorted and rearranged by currents so as to form the terrace and embankments we now find. In the deeper portions of the Jake the lime precipitated from the waters was mingled with clay and sand and now appears as marly-clay. The abundant precipitation near the shore may also have been due, in part, to the greater abundance of nuclei which tended by their presence to induce crystallization AZLOLIAN SANDS. The accumulations to be described under this head consist mainly of sand that has been blown about by the wind and finally deposited in banks or dunes which sometimes cover large areas. The first acquaintance the explorer in the Great Basin usually makes with the material forming these deposits is when it is in motion and fills the air with clouds of dust, sand, and gravel, which are blinding and irritat- ing, especially on account of the alkaline particles which saturate the 154 * GEOLOGICAL HISTORY OF LAKE LAHONTAN. atmosphere at such times. Dust-storms are common on the deserts during the arid season, and impart to the atmosphere a peculiar haziness that lasts for days and perhaps weeks after the storms have subsided. Whirl-winds supply a characteristic feature in the atmospheric phenomena of the Far West especially during calm weather, as noted already, and frequently form hollow dust-columns two or three thousand feet or even more in height, which may many times be seen in considerable numbers moving here and there over the valleys. The loose material thus swept about at the caprice of the winds tends to accumulate on certain areas and forms dunes or drifts that at times cover many square miles of surface. During its journey across the country the material which finds a resting place in the dunes becomes assorted with reference to size and weight, so that the resulting sand-drifts are usually homogeneous in their composition, but are character- ized by extreme irregularity of structure when seen in section. In the Lahontan basin the subaérial deposits are usually composed of fine, sharp quartz sand, but in some instances small drifts are principally formed of the cases of ostracoid crustaceans. A large area buried beneath sand dunes of post-Lahontan date occurs a few miles north of Winnemucca and extends westward from the lower part of Little Humboldt Valley to the desert between Black Butte and the Dona Schee Hills. This belt of drifting sand is about forty miles long from east to west by eight or ten milesin width. The drifts are fully seventy-five feet thick and present their steeper slopes to the eastward, thus indicating the direction in which the whole vast field of sand is slowly travelling. No measurements of the rate at which these drifts advance has been made, but their progress is evidently quite rapid, as it has necessitated a number of changes in the roads in the southern part of Little Humboldt Valley during the past few years. In some places in the same region the telegraph-poles have been buried so deeply that they required to be spliced in order to keep the wires above the crests of the dunes. The sand is here of a light creamy-yellow color, and forms beautifully curved ridges and waves that are covered with fret-work of wind-ripples, and frequently marked in the most curious manner by the foot-prints of animals, thus forming strange hieroglyphics that are sometimes difficult to translate. : POST-QUATERNARY DEPOSITS. 155 Another area of drifting sand occurs to the southward of the Carson Desert and covers portions of Alkali Valley and the desert basins south of Allen’s Springs. This train of dunes commences somewhat to the eastward of Sand Spring Pass, at the east end of Alkali Valley, and may be traced westward for at least twenty miles to the mountains on the east side of Walker River Valley. The width of the belt is not more than four or five miles. In a sheltered recess in Alkali Valley, a mile or two northwest of Sand Springs, the sand has been accumulated by eddying wind-currents so as to form a veritable mountain, rising, by estimate, two or three hundred feet above the plain. This ever-changing mountain of creamy sand varies its contours from year to year, while every zephyr that blows is busy in remodeling the rounded domes and gracefully curving crests and in alter- ing the details of the tracery that gives grace and elegance to the structure. The dunes in this train, like those northward of Winnemucca, are traveling eastward across mountains and deserts and seem little affected in their ultimate course by the topography of the country. In the desert valley south of Allen’s Spring the sand is carried up the steep eastern border of the basin and finds temporary resting places on the terraces cut by the waves of Lake Lahontan in the black basalt of its shores. The yellow sands loading these ancient terraces bring out the horizontal lines in strong relief by reason of their contrast in color and accent the minor sculpturing of the cliffs. Another region of sand dunes covering an area a few square miles in extent is located at the southern end of Winnemucca Lake and threatens to obstruct the only stream that supplies that water body. It is impossible to trace the sands forming these various dunes to their sources, but we. may be sure that they have traveled far and were not derived from the waste of the rocks in their present neighborhood. Similar areas of drifting sand occur at many localities throughout the region west of the Rocky Mountains, a number of which are known to be traveling in the same direction as those of the Lahontan basin. It is possible, as has been suggested by previous writers, that these various areas all belong to a single series, and are formed of the beach sands of the Pacific which have 156 GEOLOGICAL HISTORY OF LAKE LAHONTAN. been blown inland by the prevailing westerly winds. It seems more prob- able, however, that they owe their origin to the subaérial disintegration of the granites of the Sierra Nevada. SECTION 4.—ANCIENT STREAM CHANNELS. When the waters of Lake Lahontan subsided during inter- and post- Lahontan periods its basin became divided into separate water bodies or independent lakes, some of which were connected by streams that over- flowed from one to another. The channels eroded by these streams are interesting not only as examples of erosion, but because they contribute to the interpretation of the history of the former lake. When a large inclosed lake is reduced so far by evaporation that the inequalities of its bottom divide it into independent areas, it is evident that this fact in itself is a record of an important climatic change; when the ridges or embankments that divide a lake in this manner are cut by channels of overflow, it is evident that they may furnish some index of the length of the period of desiccation or perhaps of the date at which it occurred. The multiplica- tion of hydrographic basins by desiccation is illustrated by the present condition of the Lahontan region, as shown on Plate XXIX. The ancient lake basin is now divided into six independent drainage areas. Old channels now abandoned and dry occur in the Lahontan basin, between the larger areas of the former lake and the neighboring valleys that once formed bays along its shore. The Carson Desert is united with the desert valley south of Allen’s Springs by a deeply eroded channel of this nature, which appears to have been cut by a stream flowing northward; a moderate rise of the waters of the Carson Desert would flood this pass and reconvert it into a strait This channel is about 5 miles long, and has pre- cipitous walls composed of lacustral sediments, which are lined with the form of tufa we have called dendritic, while in the bottom of the pass there are crags of thinolitic tufa; from these records we learn that the channel was excavated previous to the rise of the lake during which tufa deposits were formed. As the sequel will show, these tufas were deposited during that U.S. GEOLOGICAL SURVEY Julius Bien & Co. Lith Jahontan Beach-~ I AN REGION. , AREAS OF THE LAHON' E AG DRAIN T IN PRESE Hydrographic Boundaries —~— 29 miles -Jinch Scale 100 ANCIENT STREAM CHANNELS. Tow portion of Lahontan history that witnessed the accumulation of the upper clays; and since the walls of the channel are composed of lacustral sedi ments, the inference is drawn that it was excavated during an inter-Lahon- tan period of desiccation. It will appear, as we progress with our history, that this is but one of a number of independent lines of proof which show that Lake Lahontan had two high-water stages, separated by a time when it was greatly lowered by evaporation, and perhaps reached absolute dryness. The ancient channels, now dry and abandoned, similar to the one con- necting Carson Desert and the desert basin south of it, occur at the northern end of Pyramid Lake Valley; one of these leads to Honey Lake Valley and the other to Smoke Creek Desert. The former, known as Astor Pass, was never deeply excavated, showing that the valley in which Honey Lake is situated must have been an independent water-body during a large part of the Quaternary. The second, however, is a pass, now partially obstructed by gravel embankments, which must have been a narrow strait during the greater part of the Lahontan period. The bottom of this pass is on a level with the thinolite terrace in Pyramid Lake Valley, as shown by aneroid measurements, and is thought to have regulated the water in that valley in such a manner as to bring it frequently to the same level. ‘This would be accomplished by allowing it to escape, at a certain horizon, on to the Smoke Creek Desert. It may be that this is the reason for the great strength of the thinolite terrace about Pyramid Lake. Another channel of a similar character, now known as the Ragtown Pass, connects the Carson Desert with the desert valley in which the Eagle Salt Works are situated. All these channels were in existence before the deposition of dendritic tufa, but the proof that they were excavated in lacustral clays is less definite. It is probable that some of them were occupied by streams before the first rise of the ancient lake. In some instances they have become partially re-exca- vated during the present period of desiccation, but usually they are still occupied by the upper clays. Other channels of this character have been examined in the Lahontan basin, but their features are not so clearly defined as in the examples described above, and their bearing on the history of the former lake is con- sequently less definite. 158 GEOLOGICAL HISTORY OF LAKE LAHONTAN, Srotrion 5.—ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. It is customary to consult the older and usually the more thoroughly consolidated stratified rocks for illustration of geological structure, but as such features are in many cases the records of the manner in which the beds were deposited, it is evident that they should occur in the newest as well as the oldest formations. It is well known that the history of the earth is a continuous record, however fragmentary it may seem at the present day, and that the processes of nature have been the same throughout the geological ages. Nowhere are these axioms more thoroughly sustained than in the recently desiccated lake basins of the Far West. As the gravels and finer sediments deposited in Lake Lahontan afford many instructive records of the circumstances under which they were accumulated, we have prepared the following brief summary of observations relating to geologic structure due to deposition, erosion, etc., believing that it will assist in inter- preting similar phenomena when observed in older rocks, where they are frequently obscured by metamorphism and other changes. STRATIFICATION AND LAMINATION, The sediments forming the upper and lower portions of the Lahontan section consist of fine, homogeneous, evenly-stratified marly-clays, which show a distinct lamination parallel with the planes of bedding. Attention is called to the lamination of these deposits in connection with other features due to deposition, as it has manifestly resulted from the slow accumulation of fine sediments in thin layers, and does not owe its existence to pressure, as is the case in many older rocks. This is evident since both the upper and lower clays are alike laminated, while the higher members of the series at least have never been subjected to the pressure of superimposed deposits. CURRENT BEDDING. The gravels separating the upper and lower Lahontan clays are char- acterized by extreme irregularity, and afford many illustrations of structure due to deposition. They were deposited in the shallow waters and were much agitated by waves and currents, and among other features present ee ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 159 ’ 9 typical examples of “current bedding,” sometimes called “ cross-bedding’ and ‘‘false-bedding,” as is abundantly illustrated in the walls of the Hum- boldt, Truckee, and Walker canons. The beautiful curves presented by these irregular beds when seen in section are represented with much accu- racy in the detailed sections illustrating the exposures observed. From the thousands of examples examined in various portions of the basin, those presented on Plates XXIII, XXIV, XXV, and XXVII, have been selected as types of this phenomenon. Not only is this structure remarkable for the grace and elegance of the curves produced, but each sweeping line and each curving stratum has an individual structure and varies through all degrees of fineness, and through very many shades and tints, which serve to distinguish it from adjacent deposits. The accuracy of the illustra- tions to which we have directed attention renders farther description of the forms presented by current-bedded gravels when seen in section unneces- sary. Examples of what may be properly designated as “drift bedding” are abundant, especially in the walls of the Truckee Cation, which furnish fine examples of the oblique stratification produced when currents sweep sand and gravel along the bottom until the edge of a scarp is reached and then deposit them in inclined layers. Under favorable circumstances this action may continue until a stratum is formed that is obliquely stratified from top to bottom, perhaps several feet in thickness, and of wide extent, as illus- trated in the central portion of the section exposed in the Truckee Canon. The deposition of current-borne débris in inclined strata sometimes takes place on a grand scale, as is illustrated by the section of the gravel deposits at the southern end of Humboldt Lake, shown in Fig. 17, and again by Fig. 20, which represents a section of a similar structure at the southern end of Winnemucca Lake. In the cation of the Walker River, evenly-bedded strata inclined at an angle of from 15° to 20° are exposed in a section that is fully 200 feet high, as represented on Plate XXVIII. In all these examples, and in many others that have been studied, the current-borne gravels composing the strata were deposited in the inclined position they now occupy, and do not owe their inclination to a movement of the beds subsequent to their deposition. Stratified beds deposited at an 160 GEOLOGICAL HISTORY OF LAKE LAHONTAN. incline are usually composed of water-worn gravel, but instances are not rare in the Lahontan basin of fine clays and marls that were formed in even layers inclined at an angle of from 10 to 20 degrees. CONTORTED STRATA. The folded and contorted appearance presented by many sedimentary beds may originate in two ways; either they were deposited in a horizontal position and subsequently disturbed, or they were laid down in agitated waters in the contorted forms we now find. The Lahontan sediments afford illustrations of each of these modes of origin. Examples of contortion and deformation in the lower lacustral clays, obviously due to motion produced by the weight of the superimposed de- posits, were observed at many localities. In the Truckee Canon, disturb- ances of this nature occur, as shown in the lower portion of the illustration forming Plate XXY. At the left of the section the stratum of marly clay has been broken in an irregular manner and one part thrust over the other; at the right, in the same section, the strata are crumpled and folded in such a manner as to form anticlinals and synclinals in miniature. Other illustra- tions of similar disturbances may be seen in the section exposed along the Humboldt, Truckee, and Walker rivers. At the top of the section shown on Plate XXV, but weathered back so as not to appear in the drawing, there is a deposit of fine yellowish sand in contorted strata resting on the upper clays. This deposit contains crystals and rosette-like masses of selenite, and is evidently water-laid—not 2olian as perhaps might be fan- cied—and from its position at the top of the section could never have been subjected to pressure or mechanical disturbance. The contortions and fold- ings of the thin sheets of sand composing this deposit are rendered espe- cially distinct, when seen in section, by the presence of iron-stained lines and bands, which indicate a character of contortion that can only be ex- plained by assuming that the beds were deposited in the irregular forms they now present. Similar contorted beds were observed in the Quaternary strata of the Mono Lake basin, California, in a bed of sand and pebbles 18 ad ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 161 inches thick, inclosed between horizontal, evenly-bedded, ripple-marked clays and sand. In this instance the iron-stained lines marking the edges of contorted sheets, form a most intricate pattern when seen in section, and in- close pockets and cells sometimes four or five inches in diameter, that are without openings and packed full of gravel and stones; in some instances the pebbles thus enclosed are an inch or more in diameter and are all well water- worn. ‘The presence of these cells filled with material of a different nature from the contorted sheets of sand, while the strata above and below the contorted layer are of fine sand and clay in even horizontal beds which show no crumpling, is evidently proof that the disturbance causing the irregularities of the deposit took place during the deposition of the strata and cannot be referred to subsequent mechanical movement. The condi- tions under which these contorted sands were accumulated are difficult to determine, but in some instances deposition seems to have taken place in shallow lakes that were greatly disturbed by winds and currents. The hypothesis which attributes the contortion of superficial strata to the action of advancing glaciers and grounded icebergs is not here admissible, as the relation of the lakes and glaciers is well known. The action of a moving ice sheet, formed by the freezing of a lake, might perhaps under certain conditions disturb the sediments beneath, and might even transport pebbles from the shore and drop them in offshore deposits; thus forming strata analogous to the exposure observed near Mono Lake. It is impossible, however, to account completely for all the phenomena observed by any of the hypotheses that have been suggested. ARCHES OF DEPOSITION. The finest example of an arch of deposition that has been observed in the Lahontan s ediments is represented in the section forming Plate XX.V, and has already been noticed in describing the exposure to be seen along the Truckee River. This, with scarcely any doubt, is a section of a gravel bar, the top of which was removed previous to the deposition of the superimposed gravels. Similar arches, but less complete, may be seen in other portions of the Truckee section, and occur in greater or less perfec- tion wherever a cross-section of a current-formed embankment or bar is Mon. Xt 11 162 GEOLOGICAL HISTORY OF LAKE LAHONTAN. exposed. That the arch represented on Plate XXYV is the result of depo- sition and not of mechanical disturbance is clearly shown by the horizontal stratification of the material above and below it. ~ UNCONFORMABILITY BY EROSION AND DEPOSITION. Wherever the junction of the medial gravels with the lower or upper clays is exposed, one is nearly always sure to find evidence of unconforma- bility, resulting usually from the erosion of the older strata. Examples of this phenomenon are shown in nearly all the accompanying illustrations which include the junctions in question. On Plate X XVII, the cross-strat- ification of the gravels filling eroded hollows in the lower clays is admirably shown by Figs. A, C,and D. On Plate XXIII, Fig. G illustrates the man- ner in which the strata filling eroded hollows are sometimes thickened ; while Fig. J shows a thinning of similar beds when deposited over a pro- tuberance of the bottom on which they were laid down. Figure K, of the same plate, furnishes an example of current-bedded gravels covering the eroded surface of the lower clays, while a second line of unconformity, also resulting from erosion, parts the gravels themselves. Sometimes the vari- ations due to erosion and deposition are complicated by the effects of sub- sequent lateral movement, as appears to have taken place in D, Plate XXIII. Unconformability by deposition alone, where erosion has but little effect, is shown in Fig. B, Plate XXVIII, which illustrates the contact of horizontal lacustral beds resting upon gravels that were deposited in in- clined strata. Other examples of a similar character may be found in many of the accompanying illustrations. JOINTING. The marly clays forming the upper and lower members of the Lahon- tan series usually break into prismatic and cubical blocks on weathering ; the vertical faces of the blocks are determined by joint planes, and the hor- izontal by planes of lamination. In many localities a more pronounced jointing occurs, forming two approximately vertical systems that are nearly at right angles to each other. Judging from the number of instances observed, at widely separated localities, the joints in question may be ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 163 traced through the entire series of lacustrine beds. The occurrence of two distinct and well-marked systems of joints in a bed of marly clay 6 feet thick, lying between unconsolidated gravels, has been noticed on page 132. This may be taken for an example of what may be seen at numerous localities. The most striking exhibition of jointing that we have observed in the Lahontan strata occurs in the upper clays on the west side of the Humboldt River, near Saint Mary’s. An arroyo has there exposed a vertical cliff 25 feet high, of homogeneous, marly clay that is cut from top to bottom by joints which divide the material into small pentag- onal prisms that bear a superficial resemblance to basaltic columns. Speci- mens of these prisms may be collected that are 2 or 3 feet in length and not over 3 or 4 inches in diameter, with sharply-defined edges; in some in- stances the diameter of the columns is much less than here indicated, the prismatic form being still well preserved. The jointing of the Lahontan sediments is of the same nature as the similar phenomena observed in the Bonneville basin, the origin of which has been the subject of some dis- cussion.» FAULTS. Two systems of faults have affected the sediments of Lake Lahontan ; the first is of wide extent and due to a recent movement along the ancient lines of displacement which gave origin to the structural features of the region; the second is of local origin, and seems to be entirely independent of orographic disturbances. Displacements of the first class will be de- scribed in a future chapter devoted to the description of post-Lahontan oro- graphic movements. The local faults in which we are interested at present are common in the soft, unconsolidated sediments of the ancient lake, but even in the most typical instances their displacement does not exceed a few feet, and, as indicated by several observations, they appear to have small vertical range, 7. ¢., their throw diminishes and finally disappears when 5\G. K. Gilbert, ‘* Post-Glacial Joints,” American Journal of Science, Vol. XXIII, 1882, pp. 25-27. G. K. Gilbert, ‘‘ On the Origin of Jointed Structures,” American Journal of Science, Vol. XXIV, 1882, p. 50. John Le Conte, ‘‘ Origin of Jointed Structure in Undisturbed Clay and Marl Deposits,” American Jour- nal of Science, Vol. XXIII, 1882, p. 233. W.O. Crosby, ‘‘ On the Classification and Origin of Joint-Struct- ure,” Proceedings Boston Soc. Nat. Hist., Vol. XXII, 1882, pp. 72-85. H.F. Walling, ‘‘On the Origin of Joint Cracks,” Proceedings American Association for the Advancement of Science, Vol. XXXI, 1882, p. 4i7. 164 GEOLOGICAL HISTORY OF LAKE LAHONTAN. traced downwards. Their hade usually approaches the perpendicular, and, as is common with the displacements in older rocks, slopes to the downthrow. In the instance represented below, however, the hade is reversed; this ex- ample occurs in unconsolidated gravels and clays of the Lahontan series at Mullen’s Gap, on the western border of Pyramid Lake. Scale of feet—vertical and horizontal the same. a — a & 5 10 Fic. 25.—Reverse fault in Lahontan gravels. The upward bend of the strata on the heaved side of this fault may perhaps be accounted for by assuming that the displacement has undergone double movement. During the first, the block to the left of the plane of fracture, as it appears in the figure, was the thrown block; its downward movement caused the ends of the strata of which it is composed to bend up- wards, as is common in similar displacements in older rocks ; afterwards the movement was reversed, and what was previously the thrown side was up- raised beyond its former position. The faulting took place in this instance previous to the deposition of the cross-stratified gravels represented in the diagram above the line of unconformability, as is proven by the fact that. the plane of fracture does not extend through them. The interval between the disturbance causing the fault and the deposition of the superimposed beds was short, as is evident from the absence of erosion along the surface of unconformability. Another illustration of the minor displacements that occur in the Lahontan sediments is given on Plate XXIII, Fig. A, which is remarkable ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 165 for the narrowness of the block cut out by the double dislocation; this double fault is one of a pair, as is shown in the following figure, which is drawn to the same vertical and horizontal scale, and represents with con- siderable accuracy the exposure observed in the canon wall. Feet el o3)0 20 49 60 80 100 Fic, 26.—F.ults in lacustral clays, Humbuldt Canun, Nevada, This section includes the upper portion of the medial gravels, the upper clays, and the subaérial accumulations forming the surface of the desert. In the walls of the Walker River Canon, between Mason Valley and Walker Lake, there are many examples of faults which shear the lacustral deposits of the Lahontan series; two illustrations of the displacements there observed are given in Figs. A and B, Plate XXVIII. In the former, the actual fault is concealed by an alluvial slope, but the dip of the strata proves that it was formed previous to the deposition of the upper clays and probably before the medial gravels were accumulated. In the latter instance (Fig. B) the faulting occurred after the last rise of the ancient lake, and affected both the medial gravels and the upper clays. The inclination of the strata in the lower portion of this section is mainly due to their having been deposited in an inclined position. In this instance, as is usually the case in the faults we are considering, the general inclination of the beds due to deposition is but little disturbed. On Plate XVII, Fig. E, a number of faults belonging to the class we are considering are represented, which cut the stratified lapilli composing the ancient craters now occupied by the Soda Lakes near Ragtown, Nevada. The faults noticed in the preceding paragraphs can only be studied to advantage when fresh sections of the Lahontan beds are exposed, and in 166 GEOLOGICAL HISTORY OF LAKE LAHONTAN, no instance is their presence indicated by a scarp crossing the surface of the deserts. The existence of faults shearing unconsolidated strata of sand and clay can scarcely be accounted for by the hypothesis of tangential strain, as has so often been done in the case of displacements in older and more consoli- dated rocks, as these beds are still horizontal and have not been subjected to the pressure of superimposed accumulations. The strata on either side of the planes of fracture are undisturbed. As the displacements are local and unconnected with any general orographic movements and in some instances die out as we trace them downwards, it seems safe to con- clude that they have resulted from some change in the strata them- selves, as is perhaps the case also with the joints occurring in the same beds. The Lahontan sediments were water-laid and are now desiccated. It may be that the contraction produced on drying will be found a sufficient explanation of the faulting and jointing that has been observed. The dry- ing of heterogeneous stratified beds must result in unequal contraction of the various members of the series, at the same time that the unequal desic- cation of various portions of the basin would complicate the resultant stress. In the Lahontan basin changes of this nature have taken place and have been accomplished by jointing and faulting. That these facts stand in the relation of cause and effect, however, is but a provisional hypothesis. STRUCTURE OF TERRACES AND EMBANKMENTS. While describing the formation of terraces and sea-cliffs it was shown that the loose material occurring on lake shores is sometimes swept along by currents and deposited so as to form a horizontal shelf bounded by a steep scarp on the lakeward slope. Owing to the mode of its formation, the structure of such gravel-built terrace is necessarily irregular, but as a whole is characterized by oblique stratification, especially on its lakeward margin, and abounds in examples of current bedding. Its material varies from accumulations of bowlders, sometimes two or three feet in diameter, through all degrees of comminution to the finest of silt and marl, and is usually of a heterogeneous character, dependent on the nature of the rock ILLUSTRATIONS OF GEOLOGICAL STRUCTURE. 167 forming the lake shores. The general structural features of a built terrace are shown in the section inserted on page 151. When a shore current bearing débris enters deep water, as illustrated by a simple instance on page 94, it commences the formation of an embank- ment, which is increased by the addition of gravel, sand, ete., in inclined strata at its end and along its sides. A cross-section of a regularly formed embankment should show a series of more or less perfect arches of deposi- tion. CONGLOMERATES AND BRECCIAS., In many of the bars and terraces described in this report the gravel of which they are composed is firmly cemented by calcium carbonate into a compact conglomerate. A similar action has taken place in some of the alluvial slopes ence submerged beneath the waters of the ancient lake, which at times has resulted in the formation of typical breccias. On the west shore of Pyramid Lake, near Mullen’s Gap, the immediate lake margin is formed of sand and pebbles that have been consolidated into a firm con- glomerate by the deposition of calcium carbonate. Similar beds were observed on Anaho Island and about the Needles at the northern end of the lake. In all these instances the conglomerate slopes lakewards at a low angle, sometimes amounting to ten degrees. his in all cases is evidently of a very recent date and in places is still being deposited. Although the youngest of the rock series, yet it is sufficiently consolidated to acquire a polish from the constant attrition of the sand that is washed over it and compact enough to be used for the ruder kinds of masonry. Similar con- glomerates which appear also to be still in process of formation were observed on the shores of Walker, Winnemucca, and Mono lakes. Breccias cemented by calcium carbonate are formed in alluvial slopes of the Great Basin above the limits of the Quaternary lakes. These deposits are usually less firm than the lacustral conglomerates, and fre- quently differ in the fact that the cementing material is accumulated most abundantly on the lower surfaces of the stones forming the deposit. The precipitation of calcic carbonate in the interstices of alluvial slopes appar- ently results from the evaporation of the percolating waters and the conse- 168 GEOLOGICAL HISTORY OF LAKE LAHONTAN. quent deposition of the salts held in solution, which act as a cement and sometimes change a loose débris heap to a compact conglomerate or breccia. Subaérial deposits of this nature are common throughout the arid region of the Far West. | OOLITIC SAND. The presence of oolitic sand on the shore of Pyramid Lake has already been referred to in connection with the general description of the lake. This material is evidently now forming, and in places has been cemented into a compact oolite by the deposition of a paste of calcium carbonate between the grains, and forms irregular layers several inches in thickness that slope lakewards at a low angle. The oolitic grains composing the beach sands are frequently a quarter of an inch or more in diameter, and would, per- haps, more properly be designated as pisolite. When examined in thin sections under the microscope each grain is seen to be made up of a large number of concentric layers of calcium carbonate surrounding a particle of sand or other foreign body which furnished the original nucleus. The spherical form of the grains and the uniform thickness of the concentric layers evidently indicates that the kernels were in motion during the slow deposition of the concentric shells of which they are principally composed. Oolitic sands occur also at a number of localities near the base of the den- dritic tufa, thus indicating that the conditions necessary for the formation of a deposit of this nature were then prevalent ‘hroughout the entire area covered by Lake Lahontan. That the chemi «al conditions favoring the formation of oolitic sands vary through wide limits is shown by the fact that they are now forming both in Pyramid Lake and in Great Salt Lake. The former contains less than half of one per cent. of solids in solution, while the latter has varied from over twenty-two to about thirteen per cent. during the past twenty years.” SURFACE MARKINGS. The surfaces of lacustrine deposits when laid bare and subject to des- iccation become covered with a net-work of shrinkage cracks and are not infrequently impressed with the foot-prints of animals; sometimes, too, the 52See table of analyses at C, page 180. COLOR OF LACUSTRAL SEDIMENTS. 169 muddy surfaces are pitted by falling rain-drops or covered with ripple marks. When the waters again cover such an area, all these records may be concealed beneath superimposed strata and thus preserved for an indefinite time. They are, in fact, as well suited to become fossilized as the records of a similar nature so common among the Triassic rocks of the Atlantic slope. The markings inscribed on the surfaces of lake beds are identical with many records that are made on the sands and mud along the ocean’s shore, and if fossilized, would in themselves give no indication of the character of the water-body on the borders of which they were formed. COLOR OF LACUSTRAL SEDIMENTS. From the study of the Triassic, Old Red Sandstone, and other forma- tions of Europe,” Professor Ramsay was led to the conclusion that sedi- ments deposited in inland waters were usually iron-stained. The reverse of this conclusion would probably have been reached had lake deposits been first studied in the Great Basin, as all the lacustral beds in that region are light colored and seldom show more than a trace of the presence of iron. Some of the inclined beds in the Walker River section have a pink tinge, due to the presence of iron, while some of the contorted sands we have described have a yellowish color. These features, however, are inconspic- uous and do not affect the statement that the sediment in question are a total exception to the rule referred to above. RESUME OF PHYSICAL HISTORY. To arrive ata satisfactory understanding of the physical history of Lake Lahontan, as recorded in terraces, gravel embankments, deltas, sedi- mentary deposits, river channels, etc., it is necessary to combine our obser- vations of these phenomena with the records of the chemical history of the lake as furnished by tufa deposits and desiccation products, with refer- ence, also, to the present physiography of the basin. Before considering the 53¢On the Physical Relations of the New Red Marls, etc.,” Quarterly Journal of the Geological Society of London, Vol. XXVII, p. 189. Als»: ‘‘On the Red Rocks of England of older date than the ‘Trias.” ibid., p. 241. 170 GEOLOGICAL HISTORY OF LAKE LAHONTAN. chemical questions connected with the present study, it may be well to see how far our observations relating to the physical history of Lake Lahontan can be correlated. The presence of vast alluvial slopes of pre-Lahontan date, on which the water-lines of the old lake are traced, leads to the conclusion that the climate of the region was arid for a long time previous to the first filling of the basin of which we have any definite record, viz., the earlier high- water stage of Lake Lahontan. ‘The discussion of this question, however, falls more properly in the chapter devoted to the consideration of Quater- nary climate. We assume, for the present, that a change from arid to more humid conditions caused the Lahontan basin to be filled to the level of the lithoid terrace, and to remain at that horizon long enough to enable its waves to excavate a broad shelf in the rocky shores. The terraces above the lithoid are of subsequent date, as is shown by the section of the higher water-lines given on page 103; as there indicated the lithoid terrace is frequently a shelf cut in the rock, on which rest the built terraces that define the Lahontan beach. At other localities the lithoid terrace is rep- resented by gravel embankments that are overplaced by much smaller structures of the same character at the level of the highest water-line. Cumulative evidence of this nature shows that the lake lingered at the horizon of the lithoid terrace for a much longer time than at the higher levels. The lithoid terrace and the Lahontan beach thus record two independent high-water stages. ‘The fluctuations of the lake during the interval between the formation of these water-lines cannot be determined from the physical records alone, but are not difficult to sketch, at least in outline, when the tufas that were precipitated from the waters of the lake are considered. ‘Turning to the stratified beds accumulated in the lake basin, we find two series of fine lacustral sediments separated by a widely- spread sheet of water-worn and current-bedded sands and gravels which were evidently deposited in shallow water. This record of two lake periods, with a time intervening when the basin was at least as nearly desiccated as at the present day, is perhaps the most positive of all the chapters of Lahontan history. That the formation of these two deposits of lake sediments may be correlated in time with the formation of the RESUME OF PHYSICAL HISTORY. can lithoid terrace and the Lahontan beach remains to be considered in con- nection with the chemical study of the lake. The great number of water-lines scoring the interior of the Lahontan basin shows that the main changes in the history of the lake were accom- panied by many minor fluctuations. The absence of an outlet renders it evident that the minor oscillations as well as the more permanent horizons recorded by the ancient terraces were due to climatic changes, the nature of which will be considered in a future chapter. From this brief réswmé it will be seen that the facts in the physical history of the lake can be correlated but imperfectly, yet give evidence that they have a definite sequence and are in fact fragments of a connected history. In the chemical studies which follow we shall be able to present some of the pages that are here missing and sketch the history of Lake Lahontan with greater completeness. OHAP LER We CHEMICAL HISTORY OF LAKE LAHONTAN. SEcTION 1.—GENERAL CHEMISTRY OF NATURAL WATERS. The investigation of the chemical history of a lake properly begins with the study of the meteoric waters that supply its: hydrographic basin. Lakes are filled to some extent by direct precipitation from the atmosphere, but mainly by tributary streams and springs; it is evident, therefore, that we should look to these channels for the sources of the dissolved mineral matter which all lakes contain. It is true that lakes are sometimes formed by the isolation of portions of sea water, or may occur over beds of salt or other easily soluble rocks; but such cases are exceptional and their abnor- mal character easily accounted for. RIVER WATER. Even rain water and freshly fallen snow are not absolutely pure, but usually contain some organic and saline matter, together with carbonic acid, nitrogen, ammonia, chlorine, etc., which have been dissolved during their passage through the atmosphere. In an arid region, like the Great Basin, where the soil is commonly alkaline, and its surface frequently coated over large areas with saline efflorescences, the dust that is carried high in the air by the winds is richly charged with soluble salts which are dis- solved by the falling rain, thus rendering it less pure than the meteoric _ waters of more humid regions. Rain water on reaching the earth dissolves the more soluble minerals with which it comes in contact, and becoming charged with carbon dioxide (carbonic acid), together with humic and crenic acids, and other organic products, it forms such an energetic solver 172 CHEMISTRY OF NATURAL WATERS. ie that but few substances can entirely resist its action. By the time the sur- face waters have united to form rills, they contain sufficient mineral and organic matter to have a complex chemical composition. On through their history, as they form brooks, creeks, and rivers, and finally merge with the ocean or some inland sea, they are constantly increasing their sum total of dissolved mineral matter, and are at the same time concentrated by evapo- ration. ‘The waters of a river when filtered from all suspended matter and evaporated to dryness leave a solid residue which is the principal portion (the more volatile substances escaping) of the foreign matter held in solu- tion. These waters are fresh in the every-day use of the term, but in fact owe their pleasant taste and, to a great extent, their health-giving qualities, to the mineral substances held in solution. In the following table the an- alyses of the waters of a number of American rivers are given, for the pur- pose of indicating what salts are contributed to lakes in greatest abundance by their tributaries. The principal impurities in nearly every instance are calcium and carbonic acid, probably combined in the waters as calcium bicarbonate; sometimes, however, calcium sulphate is in excess of any other salt, as inthe case of the Jordan River, Utah. Surface waters derive their chemical impurities mainly from the rocks over which they flow, and consequently vary in composition with the geological character of their hydrographic basins. When draining a granitic or volcanic area they are usually rich in potash and soda; when flowing over limestone they are fre- quently saturated with calcium carbonate. This is illustrated in the Far West by the streams entering the Bonneville and Lahontan basins In the former they have their sources in the Wasatch Mountains where limestones oecur, and are usually rich in calcium carbonate; potash is commonly ab- sent, and soda, if present, is comparatively small in amount. In the Lahon- tan basin voleanic rocks predominate and the streams contain a higher percentage of potash and soda than is usual in a region underlain by sedi- mentary rocks. By inspecting the table it will be seen, as stated above, that the most abundant of all the various substances carried in solution by the streams of this country is calcium carbonate. On averaging the amounts given in the tables we have 0.15044 part per thousand as the average of total solids, 174 GEOLOGICAL HISTORY OF LAKE LAHONTAN. and 0.056416 part per thousand as the average of the calcium carbonate contained in the waters of American rivers. In a table of 48 analyses of European river waters given by Bischof,™* the average of total solids is 0.2127, and the average of calcium carbonate 0.1139 part per thousand. From the analyses of 36 European river waters published by Roth,” including some of those tabulated by Bischof, we ob- tain (0.2033 part per thousand as the average of total solids; and 0.09598 parts per thousand as the average of calcium carbonate. In both Ameri- can and European river waters, so far as can be determined from the data at hand, the average of total solids in solution is 0.1888, and the average of calcium carbonate 0.088765 part per thousand. These figures may be assumed to represent the average composition of normal rivers. It will be noticed that the average for calcium carbonate amounts to nearly one-half of that for total solids. Knowing the volume of a stream and the percentage of mineral matter it holds in solution, we can ascertain the amount of dissolved matter that it contributes annually to the ocean or enclosed lake to which it is trib- utary. To one unfamiliar with such investigations the amount of solid matter thus annually transported in an invisible state from the land to the sea will appear truly astonishing. The Thames at Kingston, as determined by the Royal Rivers Pollution Commission of Great Britain, has an average daily flow of 1,250,000,000 imperial gallons; the water contains of morganic impurities 19, and of or- ganic and volatile 1.68 grains per gallon. This is equivalent to 3,364,286 pounds, or 1,682 tons (of 2,000 pounds each), of inorganic matter daily; of this two-thirds, or 1,121 tons, are calcium carbonate, and 271 tons calcium sulphate. The average flow of the Croton River, which supplies New York City, is 400,000,000 gallons daily, which contain 365,428 pounds; or nearly 183 tons of impurities; of these 47 tons are calcium carbonate.” . ‘4Chemical Geology, English edition, London, 1854, Vol. I, pp. 76 and 77. 55 Chemical Geology, Berlin, 1879, Vol. I, pp. 456 and 457. 56 Rep. American Public Health Association, Vol. I, p. 554. CHEMISTRY OF NATURAL WATERS. V5 The Hudson carries daily about 4,000 tons of matter in solution, of which more than 1,200 tons are calcium carbonate.” The Mississippi, as determined by Humphreys and Abbot,®* discharges annually 21,300,000,000,000 cubic feet of water; from the analyses of the water at New Orleans, by Dr. W. J. Jones,” we learn that the total of solids carried annually by the river amounts to 112,832,171 tons; of of which 50,158,161 tons are calcium carbonate. The amount of sediment transported by the river annually, as reported by Humphreys and Abbot, amounts to 887,500,000,000 pounds or 448,750,000 tons. The amount of solids, both in solution and suspension, carried annually to the sea, as deter- mined from the data indicated above, is approximately 556,600,000 tons. From the very incomplete observations on the discharge of the Hum- boldt River that have been made, we will assume 500 cubic feet, or, for convenience, 1,700 liters per second, as representing its average flow; each liter contains 03615 gram of solid matter in solution, which gives an an- nual transportation of about 18,000 tons; of this amount somewhat less than one-third, or approximately 5,000 tons, is calcium carbonate. In the same general manner we have estimated that the Carson, Truckee, and Walker rivers, collectively, transport annually about 10,000 tons of cal- cium carbonate. Not to overestimate we will assume that all the streams now entering the Lahontan basin carry annually 10,000 tons of calcium carbonate in solution. This estimate, although made on very imperfect data so far as the measurements of the streams are concerned, is certainly not too high, and enables one to understand whence the immense amount of calcium carbonate deposited in the form of tufa from the waters of Lake Lahontan was mainly derived. SPRING WATER. All the rain that falls does not find its way directly into the surface drainage, but a large portion sinks into the earth, and in many cases has a long underground passage before coming again to the light. During its subterranean course it takes an additional quantity of foreign matter into solution, and has its solvent power augmented by becoming more or less thoroughly charged with certain substances, such as car bon dioxide, which 67 Report of the American Paplie Health Association, Vol. i pp- “5d2-543, 68 Report on the Mississippi River, p. 146. ®See Table of Analyses A. 176 GEOLOGICAL HISTORY OF LAKE LAHONTAN. act as solvents for many minerals otherwise not easily dissolved by water. Its solvent power is also augmented by the increase of temperature and pressure which it undergoes as it descends into the earth. The waters issuing as springs, frequently with a high temperature, are almost invaria- bly found to have dissolved a great variety of mineral substances. In many instances the less soluble minerals occurring im spring waters are held in solution by the presence of carbon dioxide, or by high temperature or pressure. When such waters reach the surface they lose a large part of their dissolved gases, pressure is relieved, and they are rapidly cooled; the result is that much of the mineral matter ‘they contain is deposited about the orifices through which they discharge. The substances most commonly precipitated under such conditions are calcium carbonate, oxides of iron and of manganese, calcium sulphate, and silica. Accumulations of these substances are frequently of great extent as may be amply illustrated in any of the hot-sprmg regions of the world. Only a portion of the dis- solved matter brought to the surface by springs is thus deposited, however, and in many cases no immediate precipitation takes place. The waters, after losing their dissolved gases and becoming cooled, are usually much richer solutions than ordinary river waters, and, on joining the surface drainage, contribute large quantities of mineral matter to the neighboring streams. The solvent action of subterranean waters is frequently indicated by the porous and cellular character of certain rocks, as well as by the saves, frequently of vast size, that occur, especially in limestones. The analyses of river waters in all ordinary instances must exhibit the combined result of the solvent action of both superficial and subterranean drainage. Springs frequently rise in the bottom of lakes or beneath the sea and thus contribute directly to the solutions with which rivers eventu- ally mingle. In the case of inclosed lakes, the reaction of mineral waters, rising in dense saline solutions, is followed by interesting results, some of which will be considered in describing the tufa deposits of Lake Lahontan (postea page 221). In illustration of the chemistry of natural waters we have compiled the following table (B) showing the composition of a few of the better known American springs and artesian wells; by comparison with Table A, the greater richness of subterranean waters over surface streams is at once apparent. a ee a EEE Nev. Dec., 1872 .| T.M.Cha Ante, p.4 = 16055 .| Humboldt .-.-. Battle Mt., Truckee Lake Tahoe, Nev. Oct., 1872 tard.| F. W. Clarke . 1....| Ante, p. 42.-.. 0467 - 0073 0100 - 0033 0489 - 0093 . 0124 - 0030 - 0075 - 0023 1544 1. 0287 0477 - 0054 Walker Mason Valley, | Utah Lake.... Nev. Oct., 1872 F. W. Clarke - Ante, p. 46. -- - 0318 Trace. - 0228 - 0038 . 0131 t. 0576 - 0284 Nov., 1873...-- Jordan ..---- a ¥F. W. Clarke - Bulletin No. 9, U. S. Geol. Surv., p. 29. - 3060 Mohawk Johnson's Cy- clopedia, Vol. 1525 | S difference, Genesee. Utica, N. Y.-.- BES N. C.F.Chandler | C. Johnsou’s Cy- F. Chandler. clopedia, Vol. IV. — nn a = Ee NG ees ee ee a & - Paar) 7 ‘ = - ~ Analyst .. ena Sa enee Peal pesavesutasaesennn= Bear ..-..---| Croton -.--. -- weeee---| Evanston, Reservoir,N.Y| Reservoi: Wy. Ni Reference .- 9,U.S Geol. Survey, p.| City, 1881. 30, Sodium, Na ...----------- Poaiocvcpessas=aerwssanesnseso= 0082 *, 00298 PobamalOrn, Ke cnecchesencoccsqrsonterasranconnancnnnecens|srcorecrecnns 00154 Calcium, Ca...-.-.-.--+0--erecneere cers eeenne® 0432 00905 Magnesium, Mg «--.+----+eeeeesereeeenrceseeee . 00336 Chlorino, Cl...------+-+--222eeee ee wepeecOs 00213 Carbonic acid, COs..-.+------- rrei ocd * 02248 . 00441 Sulphuric acid, SOs ..-------++ Phosphoric acid, HPOs .--.. Nitric acid, NOs . Silica, SiOz..... Alumina, AlsOs .. Sesquioxide of iron, PexOs Sesquioxides of iron and alumina, Fe:Os and AlsOs ...---]----00-0----=> Sesquioxides of iron and manganese, Fe,0s and Mni0s Carbonates of iron and manganese, FeCO, and MnCOs Oxide of iron, FeO ..-..--+++eeee-seeeneeeeeeee renee Gecens|spesenencccccs|sescssennaseracslencs Oxide of manganese, MnO .....-.----- Dcchavsdeaenanecces|(vasesswsnsmas|=nenesscennnse Hydrogen in bicarbonates, I Bonen ncn: eacepeccessacs|eranc== Chloride and gulphate of sodium, NaCl and NaSOu .. -20}-0002 Ammonia, NHa4 ...-...0.-eenesneeeeeeeeeeeeees Organio matter .....-- Scceccnerecesee Monee Carbonates and sulphates of, Na, K and Mg. TABLE A.—Analyses of American river waters. (Reduced to parts per 1,000 by Dr. H. J. Von Hoesen.] Maumee, Ohio -- Los Angeles. --.-- Hydrant at Los | Delaware. .--. Hudson, N.Y. St. Ann’s Lock, | 4 miles above | Fort _ Craig, Richmond Water Montreal, Can. Reservoir at. Oct, 24, 1876, afler -| C. F. Chandler. - Rept. of Loledo Water Works, W0G., 1BTB =<] IBBL .2-caanoe-|-o~a---2<0esennrinnooransoenennee|smanscscnssetocs .--| FLW. Clarke) E. Waller ...- <7) Bulletin No. | Water supply of New York ...| C.F, Chandler E. N. Horsford) 0. Loew Public Health U. Geol. of Canada, | Geol. of N. J., Ano. Rept. Board of Health, Rieh- mond, Va., 1876. Geol. of N. Ae, Health, 18-2, p. —— pee ene cent enenee + 00242 + 03360 * Alkaline carbonates considered as sodium carbonates. we ON ————— Rio Grande, | Sacramento...| St. Lawrence..| Humboldt .-..| Truckee ...-.. Walker. ...... Hydrant, Sac- | S. side, Point) Battle Mt., | Lake Tahoe, | Mason Valley, ramento,Cal. des Cascades. Nev. Nev. Nov. 1873....- aenes= Sept., 1878 .--.| Mar. 30, 1863...) Dec., 1872 .....| Oct., 1872 .....' Oct., 1872 ..... W. J. Jones ..| 1S. Hunt...) T.M.Chatard.) F. W. Clarke .| F. W. Clarke - . S. Geog. | Rep Cal. State, Geol. of Cana-| Ante, p.41..-.| Ante, p.42....| Ante, p. 46..- urvey west| Board Health, ib 1863, p. 1 5 Novy., 1878... F. W. Clarke .| C.F.Chandler | C. F. Chandler. Bulletin No. 9, | Johnson's Cy- | Johnson's Cy. U. S. Geol. | clopedia,Vol.| clopedia, Vol. Surv., p.29 | IV. Iv. . 00200 00513 een w ee ceneeeeees 00115 5 wenseees . 01279 «032383 00121 + 00585 «00887 06836 00397 00831 - 01794 Trace, —nnnn ne ceceereces|eneeeeceenersees|ennee s|encaccancusscoss - 03167 «03700 . 00120 Trace. 1 Carbonic acid by difference, TABLE B.—Analyses of American spring waters. y pring [Reduced to parts per 1,000 by Dr. H . J. Van Hoesen.] Waters! =---5--2- es -esesecee----.,| Artesian well .-.. | Lexington, Ky. Date’ ci::.4 33% Foi, | aoecie SO AMUGSOOEd: Analyst -.... F sos oq|| SUP OLOrs one e Referoncese-s-2 sascee cece -| Ky.Geol. Surv , N.S., Vol. V, p. 189. Sodium, Na ....... Bites ee - 09227 Potassium, K.......... seis acl - 00919 Calcium, '@a ......:-..- Aricent . 02136 SMUG erro 8 itm eM pete ee 2 - 01805 ‘Bani Aseeeeeeseeeee shesaekis Miliecstasereneese ce Strontium, St............ RE ee ea Trace. OU) CE by eee seeker ede oer Trace. Tron, Fe -. == eared Trace.§ Manganese, Mn..... menqsoondnodcad becnscsedaeadace ChilorinenCle estes eee wewisicete asta . 07465 Bromine, Br......... Toding ele eeees= 5, Fluorine, Fl ..... Seaterte are Secesobasn4 | Sak So atoagacses Carbonic acid, CO, .... .-........ - 12160 Sulphuric acid, SOQ, ...-.........- : . 03218 Phosphoric acid, HPO... = Trace. Boracic acid, BgO,.-......-.-.- fayafall istoatarcves Sone eae Alumina, Al.Oz. Silica, SiOz Hydrogen in bicarbonates, H - Organic substances. Oxygen, O...... Carbonic acid, C Sulphureted hydrogen, H,S Os). Artesian well, “Glacier spout- ing spring.” Saratoga, NY... airns and C, F, Chandler. Am. Chemist, Noy., 1872, p. 164. 4. 72640 . 35806 . 94050 - 53470 01848 - 00057 . 01078 - 00341 7. 47400 04661 - 00060 Trace.** 5, 82603 . 00234 . 00005 Trace. . 00770 2. 015}t Artesian well.* Sheboygan, Wis. Feb., 1876 }. F. Chandl r. Am. Chemist, 1876, p 370. 9 - 1285 1. 0739 . 2352 Trace, - 0003 . 0027 - 0009 4. 2730 . 0025 Trace. - 1792 2. 0318 . 0004 Trace. - 0022 . 0080 - 0030 Trace. 9. 9814 0398 | | Manitou Spring. Maniton, Col. Oscar Loew. -. UssiG. Siwe 100th M., Vol. III, p. 618. Opal Spring Yellowstone National Park. H. Letiman U.S. Geol. and Geog. Survey Td., Wyo. Ter., 1878, p. 393. Sulphur Spring Los Angeles, Cal. An. Rep. U.S. G.S. W 100th . 45164 - 05980 » 44400 . 05860 . 00039 Trace. || M., 1876, p. 195, - 10424 Trace. - 50600F - 03516 - 16140 Trace. $0680 Tn excess. Hot Spring .. Hot Sp. Station, COPURSR: T. M. Chatard. Ante, p.49.... Hot Spring -.. Ward's Ranch, base of Gran- ite Mts., Nev. Boiling Spring. Shaffer's R'ch, Honey Lake Valley, Cal. M. Chatard, Ante 9.51 ... . 05000 - 7743 . 3554 . 3040 - 0669 . 0191 . 0094 - 0305 . 0367 . 0121 - OOL0 . 0084 1004 01941 02551 24953 1.1834 Warm Spring. Warm Spring Sta., B. & B. t., Mono Ba. sin. T. M. Chatard. Bulletin No. 9, U. S. Geol. Survey, p. 27. Brees, Soot . 5787 - 3492 . 3131 +0018 - 1310 - 1220 _ 00804 08251 1.0211 2, 06.2 Trace, “Correction for specific imate, as specific gr gravity only approx- ‘avity was not given in original analyses. Face page 176. t As carbonates. { As carbonate. As oxide. || As carbonate. {| As sodium chloride. “Ag fluoride of calcium. ttOxygen added to SiOz to form Sis of aSiOg. } Liters of gas thrown off per liter of water. liahLake| Owen's] Pyramid | Sevier Lake,) Walker | Winnemucca Van Lake...| Aral Sea. Lake, Cal. Lake, t Utah. Lake,t Lake, Nev. Nev. Ney. 1.051 |. 5 1. 003 ACO01S| Seeeeceeen Pood saenonosoces Aug., 1882.| 1872..... Sept., 1882 | Amg., 1882) |...-..--.-.<- ‘| F W.Clarke O. Loew ---.|F.W.Clarke| F. W. Clarke Chancourtois Ante, pp.57| U. S. Surv. | Ante, p.70.| Ante, p. 63. | Bischof’s|RotbChem- p-| and 58. W. 100 M., Chemical| ical Geol- Chief En- Vol. ILI, p. Geology, ogy, p- gineers, 114. Vol. I, p. 465. 1s76, p. 190. 94. 74. 890 21. 650 1. 1796 28. £40 «85535 1. 2970 8. 5025 2, 4512 Spececass 2.751 . 0733 246 . 0584 acodscedleecaepecces poo EASSecer nee mecochcacdsas + 0022 - 529 Trace. SOUSS IPS ES ones SS O28IG)|5 OLDG Leone actennen 4581 2.914 Trace. - 0797 . 157§ 5965 ceaesses Trace. SSeemacneree ssqoecencresice| pecocceccons aesce ce Kenta cdcosmsed PoConOeaosese Trace. 0008 119. 496 13. 440 1. 4300 5. 693 3. 8386 Abeccca6|SesncaEseseaeel sa cansesccced|losccostecscsos) becscoetédod beacctebSsccsn | besocdiccsesdas - 0029 a aeeee 13. 140 BURSON |e mee each « 47445"") « 3458** 5. 267§ - 0918 7. 671 9, 362 - 1822 9.345 + 52000 +1333 2. 555 3. 3368 cEnaecias Trace. seecoscecesas)| hsoSe5e5005595| hoceoeeses6s) SSeosrisoce-mso) ee sooss eerea - 0011 BS LLeSR Trace. sdcscnssesccy lesccen ccaccace] bsecengssao4 sssacossteceed| Soe Sansseoas|| bits BAS cee Trace. Ssoncasosssad lscontishonedsss| bossasendaod bococsasensasd HS Sechases5s=5| Bacaasooccen gacoshee . 164 O8SSi| aaene see eeee eal - 00750 - 0275 - 180 + 0032 shdeeess Trace. sbotoocscndos| secenpssecasell esoasccesss| soot aadcconseal estossdaan Secs bescososcoss Trace Trace. 205. 500 60. 507 3. 4861 86. 403 2. 50150 3. 6025 22. 600 10. 8416 s Peroxide. ** Carbonic acid by diffence. Taste C.—Analyses of the waters of inclosed lakes. ; [Reduced to parts per 1,000 by Dr. H. J. Van Housen.) Elton Lake .| Great Salt | Great Salt Great Salt | Humboldt* | Indewsk | Soda Lake, Soda Lake, Lake. Lake. Lake. Lake. Lake. near Rag- near Rag- town, Nev., | town, Nev., at 1 foob| at 100 feet below sar-| below sur- face. face. 1. 2200 |. : } LOOT | aransen omens 1.101 1.101 1.048 1,156 Apr. 11008 Mar.1h, 1808 a Pe .| October. 1850... .| 1869 a tT CR CR eee creinigiepkomies | LFF alee | Dah y 10, TOUR ote dooce Seal conmenmsmneaeel ua ‘Terrell ..-.| Terreil . -| H. Rose. ia --| 0. ; -Chatard) Hitchcock ..| O. Loow .._. Geo- Bischot's U.S. Geol. ‘8 -S. B Ante p.70. | Ante,p.70. | Bulletin No. | Lartet Geo- | Appendix JS Chemical xp Expl. 40th | logieul Ex- 2 9 U. S.| logical Ex-| Ann. Rep. Geology, Geology, , q ears 1877, ploration Geol. Sur-| ploration| Chief En- Vol I, p. Vol. I, p. ol. If, p. ol, I, p. of Dead vey, p. 26. of Dead| gineers, 05. 403-405, 528. Sea, p. 284.) 1576, p. 190. 74, 890 21, 650 + 27842 94. 050 41. 632 40. 206 18.100 eee sean ae } - 06083 529 2.200 2.425 RIG lean eee 2.751 0586 oe Sere eee net Reon reese nat, bases 0022 +106 |. : fr ‘ Ke Le eee -520| ‘Trace. 4881 45, 598 - 29 5905 Trace. =|. -s020-----00+ ‘ suanndssuSnamy) anes aonalenealauxewnsdnansiacliwewxocegcucun|saneunseepelsn|oteel ae saxcfel Gaskins mmaimee (ake raetdas at ian nae nnee 170. 425 159, 498 166. 890 171. 936 124, 454 83. 46 seeneneececece 15. 650°" 18. 658** 14, 405°"). weclen - 03010 8.065 ui, 771 11.43 6.520 TRFROG) SU feetense veces) casce ns cenccsfeweccnneenyees|coccnvenceeses|snccausascecss|* sauheeHe das xt|taeakita sean ae Sdewagncaeuesfwsaneusd FRESHENING OF LAKES BY DESICCATION. 225 As these lake basins were never filled to overflowing, we are forced to conclude that influx was counterbalanced solely by evaporation, and that during periods of extreme desiccation the saline deposits became buried and absorbed by the marls and clays which accumulated in the valleys. Having analyses of the waters of an inclosed lake, and knowing also the composition of its tributaries, we can determine, at least approximately, the length of time it has been in existence, provided no salts previously deposited were dissolved when the basin commenced to fill. For the purpose of making a computation of this nature in the case of the lakes now occurring in the Lahontan basin, the following table has been com- piled from analyses given in chapter ILI. TaBLE D.—Composition of the principal lakes and rivers of the Lahontan basin. LAKES. P. id | Walk | | i yrami alker : Fe Bes Tn 1,000 parts of water. _| (average of | (average of ‘Winineintioss,| Average. || Probable ip et in average compo- |4 analyses).| 2 analyses). Hab Silica (SiOe) .......--...------ 0. 0334 0. 0075 0. 0275 0. 02280 || Silica (SiO2).-....-----.---.-. 0. 02517 Calcium (Ca)...--------.--.-- 0. 0089 0. 02215 0. 0196 0.01688 || Calcinm carbonate (CaCQs) . 0. 03221 Magnesium (Mg).....-------- . 0.0797 0. 0383 0. 0173 0.0451 || Magnesium carbonate (Mg Potassium (K) | 0. 0733 trace 0. 0686 0. 04730 (C0 eeeisssentaeceSsaake toe | 0. 20483 Sodium (Na) ----..-<.-----.- 1.1796 0. 85535 1. 2970 1.11065 || Sodium carbonate (NaCQs). . 0. 48327 Sulphuric acid (SOa).--------. 0. 1822 0. 5200 0. 1333 0. 2785 Potassium chloride (KCl) -.-| 0. 09894 Chlonme(Ci)--5 ==. -.=----ee=- 1. 4300 0. 58375 1. 6934 1.23488 | Sodium chloride (NaCl). --.. 1. 94244 Carbonic acid (COs) by differ- | || Sodium sulphate (Na2SOx) --| 0. 40195 QuGGE Ssssnestoa cesStoscecace | 0. 4990 0. 47445 We 0. aod 0. 43975 | Total (99.00 per cent. ac- ean 3 Motali sence 3-2 -5-5--—H- | 3. 4861 2.50150 3. 6025 3. 19586 counted for) .......-.. 3. 18881 | RIVERS, In 1,000 parts of water. Humboldt. | Truckee. Walker. Average. | Probable combination in average compo- sition. Silica (SiOz) ......-....---.-.- 0. 0326 0. 0137 0. 0225 | 0.0229 || ] ae Alumina (ALO,) ... .....---. CONTE Soo ode ol Rs ope eee nce] Rater ASE eee nC CGaloium (Ga): - i} | = Margaritana margaritifera, Linn..-..)...... Bescon ) + | ae. ll Limnophysa sumassi, Bd ...... ---- Neer al ea + + Anodonta Nuttalliana, Lea .... ..-. e550 + + | + |) humilis, Say .-- .----- ee | -----| + | 4 Spherium dentatum, Hald ........-.|.....-|.-...- | + + Physa humerosa, Gould.-.-.....--...|.-... |------ + tr striatinum, Lam .--...-- eerie seen } + + Pompholyx effusa, Lea.--... ..--- + + + }+ Visidium ultramontanum, Prm .... |....--|...-.- + | + Carinifex Newberryi, Lea.......-..|.-....|..---- + | + COMMPNESSUM, YM 25). cc eal ws eoleceene | + | + || Ancylus Newberryi, Lea.......... |...-.. Jose | este BHT Helisoma trivolvis, Say ..--..--...-.|.-----|------ + | + | Ampicola longinqua, Gould ...-....|..---.|------ + )+ JmMmMoOns; GON. sn -= eoeees| See es | see | aan + Pyrgula Nevadensis, Stearns. ......|------|..-.-.]------ + Gyraulus parvus, Say ..-.---.---.-. |...-.. + + | + || Fluminicola fusca, Hald.-..-.....-- 37 VOLMICUIATIS: GOUIG pease se eeee| seneen lcm + Valvata virens, Tryon ...-..--.... a Menetus opercularis, Gould ..-...--.|......|..---- ) + + Vallonia pulchella, Mull ar Limnea stagnalis, Linn ....-:...--.-|--2---|------|-<2-- + Succinea stretchiana, Bd ae Limnophysa palustris, Mull .--...-..!....-. |} + + | + || Pupilla muscorum, Linn... -...--. + bulimoides, Lea -.....--|---- A ecaae + + OT i} In arranging the fossils according to their geological horizons we have considered the lower lacustral beds as, at least in part, contemporaneous with the lithoid tufa; the medial gravels have been correlated in time with the thinolitie tufa; and the upper lacustral clays with the dendritic tufa. As indicated in the list, only a single species (Pompholyx effusa) has thus far been derived from the lower lacustral clays. This was found in great abundance in the lithoid tufa on Anaho Island, and was equally com- FOSSIL MOLLUSKS. 241 mon in other localities at a corresponding geological horizon. This is the most abundant and characteristic fossil of the Lahontan sediments ; it occurs from the base of the oldest of the tufa deposits all the way through the series, and is one of three species of mollusks found living in Pyramid Lake at the present day. All the fossil shells obtained are of recent species, and the majority have been found living in the Great Basin. A comparison of the living and fossil forms has shown that the fossils are depauperate, and exhibit greater variations in the size, thickness and sculpture of their shells than occur in living examples of the various genera and species when obtained from regions where they find a congenial environment. In this connection Mr. Call says: “The wide range of Pompholyx in Lahontan beds makes possible a valuable comparison of the same species from localities representing stages of the lake widely separated in point of time... ... . Specimens taken from the lithoid tufa on Anaho Island, in Pyramid Lake, when compared with those from horizons correlated with the dendritic period present the widest range among individuals. The shells from both localities are higher than Pyra- mid Lake form, are much thinner, and the coiling of the whorls is much looser. The lithoid tufa specimens present a large proportion of costate forms, the ratio being as 1 to 2, while in recent specimens the ratio is as 1 to 32. The recent species approximate P. effusa, var. solida Dall, while in sculpture and elevation the earlier forms of tlie lithoid tufa approach nearest to the typical P. effusa, Lea.” Comparative measurements of Pompholyx effusa from deposits of lower and upper Lahontan beds, and of specimens found living in Pyramid Lake, show that the average size of the fossils from the older horizon is below that of the Pyramid Lake specimens; while those from the upper Lahontan sedi- ments are larger than the living examples. On comparing the size of the Pyramid Lake specimens with the average of the same species from fresh water localities in the same region, it was found that the shells from fresh water were larger than those obtained from Pyramid Lake, which, it will be remembered, is somewhat saline and alkaline (see analyses, pages 57 and 58). A large number of measurements of fossil and living forms, shows that the Mon. x1——16 242 GEOLOGICAL HISTORY OF LAKE LAHONTAN. Lahontan fossils are smaller and exhibit greater variation than the same species when living under normal conditions. On comparing the size of Pompholyx from Anaho Island (lower Lahontan), “ white terrace” (upper Lahontan), and White Pine, Nevada, (living), the ratio of 63: 88: 100 was obtained.” . The investigations of conchologists have proven that there are ai least three variations of environment which may cause depauperation in fresh water mollusks, viz., salinity, low temperature, and scarcity of food. As regards salinity, it has been shown that a sudden change from fresh to saline water, i. e., to water resembling that of the ocean, is fatal to fresh-water mollusks. When the change is gradual the life of the spe- cies may be maintained until a considerable degree of salinity is reached, but the limit has not been determined, and is known to vary widely with different species. ‘To make the experiments in this direction definite and comparable with the gradual changes which take place in the waters of inclosed lakes, would require a much greater length of time than has yet been devoted to the subject. Enough has been determined, however, to show that a gradual increase in the salinity of a lake would be accompanied with the depauperation and decrease of its molluscan life; should the salinity continue to increase until a condition approximating that of the ocean was reached, the molluscan life would become nearly if not completely extinct. We may reasonably conclude, therefore, that the waters of Lake Lahontan were not strongly alkaline or saline during the time the sediments and tufas so richly charged with fossil shells were deposited. It is perhaps well to mention in this connection that there is no reason to doubt that the mollusks whose shells are found in such abundance actually inhabited the ancient lake. They could not have been contributed by inflowing streams and are not found in exceptional abundance where springs entered the lake. The degree of salinity attained by the ancient lake cannot be deter- mined, but, as we have seen, must have been low, at least during the high- water stages. This conclusion is most definite in the case of the upper lacustral marls which are frequently charged with the shells of Anodonta, a 7 These measurements refer to the length of the shells. ABSENCE OF MOLLUSKS IN SALINE LAKES. 243 In the experiments that have been made in reference to the influence of saline waters on the life and growth of fresh water mollusks, the effect of common salt (sodium chloride) has principally been considered. The lakes of Nevada, however, are characterized by the presence of alkaline carbonates, which it is believed have a more decidedly deleterious effect on the life and growth of fresh water mollusks than common salt. This con- sideration lends still greater weight to the conclusion that the waters of the former lake were not highly charged with mineral matter during the time the fossil-bearing sediments and tufas were formed. The condition of several of the enclosed lakes of the Great Basin at the present time, however, indicates that a very moderate degree of salinity and alkalinity is perhaps favorable to the growth of fresh water mollusks. Franklin, Ruby and Humboldt lakes are all more highly charged with salts than is the case with ordinary lakes and streams (the total of solids in solu- tion, however, not exceeding a small fraction of 1 per cent.) but have an abundant molluscan fauna. The inference is that a decided although indefi- nite degree of salinity is requisite to produce depauperation. In the more strongly saline and alkaline lakes, of which Mono, Abert and Great Salt Lake are examples, careful search has been made for living mollusks but none have been found. ‘These lakes are believed to be entirely destitute of both molluscan and piscine life. As Lake Lahontan never overflowed, it is safe to conclude that its waters at all times must have been less pure than those of ordinary lakes with outlet. The depauperation of its fossils and their variation in size at various horizons, are thus correlated with known saline and alkaline condi- tions, which also varied with fluctuations of lake level. We conclude, therefore, that at least one cause of the depauperation of the mollusks now found fossil was the chemical composition of the waters they inhabited. In reference to the evidence furnished by the Lahontan fossils as to the climate of the Quaternary, a conclusion seems impossible at this stage of the investigation, for the reason that a sufficient cause for the observed variation and depauperation of the shells has been found in the chemical character of the waters in which they lived. If we postulate a cold Quater- nary climate, the logical sequence would be a depauperation of the fresh- 244 GEOLOGICAL HISTORY OF LAKE LAHONTAN. water mollusks; but since a similar change would result from the necessary chemical condition of the waters of an inclosed lake in which concentration had been long continued, no definite conclusion as to the effect of the low temperature seems possible. On the other hand, a warm Quaternary cli- mate would presumably be favorable to the growth of mollusks, but even if the climatic conditions were favorable, a more potent element in their environment caused the shells to become depauperate. Mr. Call’s studies have shown that the molluscan fauna of Lake La- hontan was characterized by the predominance of the Limneide. This family of mollusks at the present time is of world-wide distribution, but is found most abundantly in cold-temperate and subarctic regions. During the Quaternary it may be presumed to have had a similar isothermal distri- bution. Thus in a very general way it might be inferred that the Quater- nary climate in the region of Lake Lahontan was colder than at present. The wide distribution of the Limnewida, however, and their known powers of enduring marked changes of environment, render this conclusion of doubtful value. The majority of the molluscan species that inhabited Lake Lahontan are still living in the Great Basin, and so far as this branch of the palzeontological evidence bears witness, we see no reason for conclud- ing that the former climatic conditions differed materially from the present. The only safe inference seems to be that the climate of the Great Basin during the life of the mollusks we are considering was not characterized in mean temperature by extremes of either heat or cold. As regards the scarcity of food in Lake Lahontan, in reference to the depauperation of its molluscan fauna, we know that the mollusks now found fossil, like their living representatives, must have subsisted mainly on con- vervoid growths. This form of vegetable life flourishes not only in fresh, but also in brackish and alkaline waters, as may be seen in the various lakes of the Great Basin at the present time. There is therefore no reason to conclude from the probable composition of the waters of Lake Lahontan that food of the character required by mollusks was not abundant. The profusion of fos il shells in the sediments and tufas leads to the same con- clusion, for without sufficient food molluscan life could not have been so prolific. SEMLFOSSIL SHELLS. 245 The fossils that might be expected to throw the most light on the cli- matic problem are the mammalian remains, but, unfortunately, up to the present time these have been found in such limited numbers that but little evidence as to the nature of former climatic changes can be derived from them. Throughout Lahontan history Pompholyx effusa was the most abundant species in the molluscan fauna, but only a very few individuals of this genus have been found living in the present lakes of the basin. Moreover, the dead shells of Pyrgula Nevadensis occur in profusion on the shores of Pyramid and Walker lakes, but have not been discovered among Lahontan fossils. This species is probably now living in the lakes of the region, as is indi- cated by the fresh appearance of the shells, in some of which the soft parts of the mollusks are still adhering. The occurrence of Pompholyx throughout the Lahontan series and its rarity in the existing lakes of the basin, as well as the absence of Pyrgula from Lahontan fossils, and its abundance in a semi-fossil condition, are be- lieved to indicate that there was an interregnum between the time of Lake Lahontan and the beginning of the present lakes of the basin. If our read- ing of the records is correct, this time of change was a period of extreme desiccation during which the lakes of the region evaporated to dryness, their salts becoming buried beneath playa deposits, and their molluscan life nearly if not completely exterminated. The absence of Pyrgula in Lahontan sediments, and its abundance ina semi-fossil condition about the shores of the present lakes, in which it is now rare, seems explicable on the assumption that it was introduced into the basin at a recent date and found a congenial habitat in the mildly saline waters of Pyramid and Walker lakes. Subsequently these lakes became too saline and alkaline for its existence, and it was nearly if not completely exterminated, so far as they are concerned. The present chemical compo- sition of the lakes in question is believed to indicate about the limit of salinity or alkalinity that fresh-water mollusks can sustain. The cases of a minute crustacean of the genus Cypris occur through- out the Lahontan series, and at times are so abundant that they form the principal portion of strata for several feet in thickness, as may be seen in 246 GEOLOGICAL HISTORY OF LAKE LAHONTAN. the walls of the Truckee Canon. At the base of the layer of dendritic tufa exposed along the Humboldt and Truckee rivers this fossil occurs in pro- fusion, frequently intermingled with the shells of Pompholyx. On the bor- ders of the Carson Desert the cases of Cypris have been accumulated by the wind in such quantities as to form small drifts resembling sand dunes. What specific name this fossil may bear has not been determined, but spe- cies with which it is evidently closely related are known to live in both fresh and salt water. Its value, therefore, as indicating the nature of its environ- ment in Lake Lahontan is indefinite. FG, 32.—Larval cases of a caddis fly encased in lithoid tufa. At a single locality, the larval cases of a caddis fly were obtained, which were coated over and partially imbedded in lithoid tufa (Fig. 32). This fossil is very similar to the larval cases of the caddis fly now found abundantly in streams and lakes, and, so far as the evidence goes, indicates that the waters in which the fossils were formed were not intensely alkaline or saline. The worm-like larval cases of a fly occur in the tufa about the Soda Lakes near Ragtown, but these are evidently of quite recent date and cannot be considered as Lahontan fossils. The fossil from the Lahontan basin that will probably be considered by both geologists and archeologists as of the greatest interest, is a spear- MAN IN THE QUATERNARY. 247 head of human workmanship. This was obtained by Mr. McGee, from the upper lacustral clays exposed in the walls of Walker River Canon, and was associated in such a manner with the bones of an elephant, or mastodon, as to leave no doubt as to their having been buried at approximately the same time. Both are genuine fossils of the upper Lahontan period. The spear- head is of chipped obsidian and is in all respects similar to many other implements of the same nature found, commonly on the surface, through- out the Far West. It was discovered projecting point outwards from a ver- tical scarp of lacustral clays 25 feet below the top of the section, at a local- ity where there were no signs of recent disturbance. This fossil, which is the only evidence at present known of the existence of man on the shores of the Quaternary lakes of the Great Basin, is represented natural size in the following figure. Fic, 33.—Spear-head of obsidian from Lahontan sediments. The only fossils of a vegetable nature thus far referred to Lake Lahon- tan are certain problematic, stemlike tubes, from one to two inches in leneth, and approximately the thirtieth of an inch in diameter, which occur in great profusion at the base of the lithoid tufa on Anaho Island. In some places the lower two or three feet of the tufa is very largely com- posed of these remains. Our reference of these fossils to the vegetable kingdom is only provisional, however, as they have been examined by several skilled palzeontologists without having their relations definitely deter- mined. It has been suggested that they are the casts of grass-like stems, but their uniform diameter and the absence of joints seems to preclude this determination. In describing the variations presented by Pompholyx from Anaho Island, Mr. W. H. Dall has spoken of these fossils as the casts 8 of the leaves or needles of the pine;” it is possible that this may be the true explanation of the enigma. Science, Vol. I, 1883, p. 202. 248 GEOLOGICAL HISTORY OF LAKE LAHONTAN. No leaves or vegetable stems of any kind, excepting the fossils men- tioned in the last paragraph, have been found among the records of the old lake, and no drift timbers seem to have been deposited in the bars and embankments that have been examined. The absence of such fossils appar- ently indicates that the shores of the former lake were not heavily wooded. The borders of our Northern lakes at the present day are thickly clothed with forests and their shores encumbered with stranded logs and stumps in such quantities as to have considerable influence on the character of the shore phenomena resulting from wave action. Had the shores of Lake Lahontan been as densely wooded as are those of Lake Michigan, for example, it seems impossible that abundant records of the fact should not have been discovered during our sojourn in the basin. A superficial microscopical examination of the sediments of the ancient lake has shown that they are richly charged with the silicious skeletons of infusoria, and sometimes abound in sponge spicule. A detailed study of these fossils was not practicable, and, as these forms of life are so widely distributed and live under such diverse conditions, it seems doubtful in the present instance, if a more critical examination would greatly assist in solv- ing the chemical and climatic problems with which the student of the Qua- ternary geology of the Great Basin is principally concerned. No fossils have been found in the thinolitic tufa, although careful search has been made at many localities. At times shells may be seen in the open spaces between the crystals, but these are believed in all cases to have been accidentally introduced at a recent date. The absence of all life records in this deposit strengthens the hypothesis that the thinolite was crystallized from waters highly charged with mineral matter. In correlating the various Lahontan deposits we have considered the thinolite as stratigraphically intermediate between the lower and upper lacustral clays, and, at least in part, contemporaneous with the medial gravels. The fossils obtained from the medial gravels are of fresh-water species, but were collected near the borders of the basin and at a greater elevation than the upper limit of the thinolite. The fossils may thus rep- resent a stage in the recession or in the refilling of the lake when its waters were not so dense as when the thinolite was crystallized. In the Humboldt aia seal SUMMARY OF PALAONTOLOGICAL EVIDENCE. 249 Canon where fossils were found in the medial gravels, it is probable that the strata are in part a flood plain deposit, accumulated when the lake was below that horizon. SUMMARY. The evidence derived from organic remains indicates that Lake Lahontan throughout: its higher stages was never a strong saline and alkaline solution. HKven during the abundant precipitation of dendritic tufa the lake was inhabited by mollusks in great numbers, and was probably also the home of Teleost fishes of large size. During the thinolitic stage, when its waters were greatly concentrated by evaporation, the absence of fossils indicates that it was uninhabited by either fishes or mollusks. The life history of the lake, as we know it at present, cannot be con- sidered as affording definite information in reference to the character of the climate during the Quaternary. The reason is that any change in the molluscan life that might be due to climatic oscillations, is complicated and masked by the effects produced by variations in the chemical composition of the waters. When other basins in the same region are explored, especially those which found outlet, the character of their mollusean fossils may lead to positive conclusions in this direction, for in such instances the influence of an abnormal chemical condition of the waters on the growth of mollusks would be eliminated. CHA PDER AY LT. RESUME OF THE HISTORY OF LAKE LAHONTAN. The history of the fluctuations of the Quaternary lake of northwestern Nevada is recorded in various ways, as has been described in the last three chapters, which treat it from the physical, chemical, and biological stand- points; in the present chapter it is our purpose to present briefly the con- clusions based upon these various lines of evidence. The phenomena observed have great diversity of character, but when interpreted in terms of geological history, they support and supplement each other in such a way that the conclusions drawn are believed to be well sustained. Moreover, the facts observed in the Bonneville basin and in more than a score of desert valleys throughout the northern half of the Great Basin which contained contemporary water-bodies, harmonize with the interpretation of the La- hontan record here presented. The fact that all the minor basins in the arid regions of the Far West are filled to a depth of many hundreds of feet with alluvium and lacustral sediments, together with the occurrence of the beach lines of the Quaternary lakes on the surface of the vast alluvial cones, leads to the conclusion that all these basins were barren deserts before the rise of the Quaternary lakes. The pre-Lahontan condition of northwestern Nevada must have closely resembled its present character, but at times it was probably completely desiccated. The change of climate admitting of the existence and gradual expan- sion of lakes in the various valleys throughout the Great Basin caused a number of those situated in northwestern Nevada to rise sufficiently to unite and form a single irregular water-body 8,922 square miles in area, This 250 RESUME. 251 was the first rise of Lake Lahontan. Like all inclosed lakes it must have fluctuated in depth and extent with the alternation of arid and humid seasons, and risen and subsided also in response to more general climatic oscillations, which extended through years and perhaps embraced centuries. Finally the climatic conditions which favored lake expansion ceased, and a time of aridity, like that which preceded the first rise, was initiated. The lake slowly contracted until its basin reached a greater degree of desiccation than that now prevailing. This was the inter- Lahontan period of desiccation. During the first rise lacustral marls and clays were deposited through- out the basin; the depth of these is unknown, but they certainly exceed 150 feet in thickness. The waters were saturated with calcium carbonate and the precipitation of great quantities of compact stony tufa took place. Deposits of tufa were formed on rocky slopes throughout the basin, and are not especially abundant at the mouths of streams. This is thought to indicate that although the waters were saturated with calcium carbonate, they were not highly charged with other chemical substances. This con- clusion is sustained by observation of conditions under which a similar tufa is being deposited in existing lakes, and also by the presence of gasteropod shells in the lithoid tufa in great abundance. The time of low water, and perhaps of complete desiccation, that suc- ceeded the first rise of Lake Lahontan, is recorded by stream channels carved in the lacustral beds and by current-bedded gravels and sands super- imposed upon previously formed strata. Sections of inter-Lahontan gravel deposits have been observed wherever the material filling the lake basin is well exposed, and furnish indisputable evidence that the lake was greatly lowered before the gravels were deposited. These gravels were in turn covered by a second lacustral deposit, thus forming a tripartite series, a counterpart of which exists in the Bonneville basin. The first formed tufa deposit was exposed to subaérial erosion during the inter-Lahontan period of low water and became broken and defaced. The character of the next succeeding tufa deposit indicates that a change had taken place in the chemical conditions of the waters of the lake when the basin was again partially flooded. This alteration in the com- position of the salts dissolved in the lake is thought to have been brought 252 GEOLOGICAL HISTORY OF LAKE LAHONTAN. about by a partial deposition of the saline matter accumulated during the first high-water stage, at the time of the inter- Lahontan period of desiccation. The tufa superimposed upon the lithoid variety is known as thinolite; it is composed of well-defined erystals and is without fossils. It was evidently precipitated from a more highly concentrated chemical solution than that from which the lithoid variety was deposited. That this was the case is rendered evident, since the crystalline variety occurs only low down in the basin, while the lithoid tufa may be found within 30 feet of the highest terrace carved by the waters of the ancient lake. After the crystallization of thinolite had been carried on for an indefi- nite period, the lake rose to within 180 feet of its first maximum, and the heaviest deposit of calcium carbonate found in the basin was precipitated. During this stage the lake was not strongly saline, as is shown by the abund- ance of gasteropod shells obtained from the sediments and tufas accumulated during this portion of its history. After the precipitation of the dendritic tufa, the lake continued to rise and at last reached a horizon 30 feet higher than the first maximum. During this expansion the waters lingered but a comparatively brief time at the highest level and then slowly subsided. The increase in depth after the deposition of dendritic tufa is shown by the presence of lacustral sediments upon that deposit. The structure of the higher bars and embankments about the border of the old lake basin, proves conclusively that the greatest lake expansion was during the second rise. With the last recession of the lake all portions of its basin-were brought within the reach of wave action, and the tufa deposits sheathing its interior were broken, and the fragments swept away by currents, and built into em- bankments and terraces. The waters continued to fall until the basin was completely dry. All the salts not previously precipitated were deposited as desiccation advanced, and became buried and absorbed by playa clays. The proof of the occurrence of this time of desiccation is furnished by the comparatively fresh condition of the existing lakes of the basin, and by the change in the molluscan fauna which took place since the last high-water period. The duration of this post-Lahontan arid period is unknown, but . ar RESUME. 253 it was finally terminated—probably less than 300 years since—by an in- crease in humidity. The present lakes then commenced their existence. _ Throughout its history, Lake Lahontan has been subject to a multi- tude of minor oscillations, as is indicated by the banded and stratified char- acter of the tufa deposits lining the interior of its basin. The character of the climatic changes which brought about both the great expansions and contractions of Lake Lahontan; as well as the minor fluctuations to which it was subject, will be indicated, so far as the writer has been able to interpret the records, in the following chapter. CAD ACE UL Enea vol site - QUATERNARY CLIMATE. In preceding chapters we have considered the physical, chemical, and biological histories of Lake Lahontan, as determined from facts gleaned here and there in its now empty basin. In each of these chapters reference has been made to the climatic conditions on which these various elements of history depended. In the present chapter it will be our aim to review the evidence afforded by the records of the ancient lake which have a bear- ing on the determination of the climatic conditions that permitted of its existence. The investigations of naturalists have shown that the fauna and flor: of a region are expressions of its climatic condition. To the geologist, the physiography of a country reflects, with nearly equal clearness, the effects of that resultant of a plexus of independent meteoric forces, designated by the term climate. Hach year, as the seasons succeed each other, the geo- logical changes, that are ever active, although so slowly and so silently that many times they escape observation, may be correlated with the ele- ments of climate on which they are most closely dependent. Of the atmos- pherie forces at work, on every hand, in remodeling the earth’s surface, those dependent upon humidity and temperature are the most obvious. These vary in intensity with the seasons, and at times their independent workings may be observed. Throughout the geological ages these same invisible agents of the air have never ceased to work changes on the earth, at times surrounding it with warmth, beauty, and life, and again, as the eons passed on, blotting out the fair picture themselves had drawn, and replacing it with cold, desolation, and death. - The general effects of climate are so well known that one may predict the resuits produced by its various elements on the aspect of a given region. 204 TOPOGRAPHY OF ARID REGIONS. 255 The geologist is enabled to reverse this process, with greater or less success, and, from the records in the rocks, determine the prevailing climatic condi- tions of bygone ages. The interpretation of the Lahontan records in terms of climate is at the same time the most interesting and the most difficult of the problems that their study has suggested. ‘The character of the Quater- nary climate of the Great Basin has been treated in a comprehensive manner by Mr. Gilbert in a monograph on Lake Bonneville, which, it is expected, will soon be published. We are thus, not unwillingly, constrained to con- fine our studies to the evidence afforded by the records of Lake Lahon- tan. Our attention will necessarily be mainly directed to the questions of humidity and of temperature. Among the topographic characteristics of arid regions are angular mountain tops, canons with precipitous walls, and alluvial cones where streams from the mountains lose their grade upon reaching the valleys. The last of these features is perhaps as striking as any of the others, and is of special interest in the present discussion. Many times the bases of mountains are completely encircled by a sloping pediment of unassorted debris, either angular or rounded, which is the most abundant at the mouths of canons. Such accumulations form alluvial slopes, and when the débris occurs in more or less conical or fan-shaped piles it forms alluvial cones. These deposits have been studied especially by Drew” and Gilbert;*® by the former in the arid regions of Southern Asia, by the latter in the Great Basin. As described by Gilbert, “The sculpture of a mountain by rain is a twofold process—on the one hand destructive, on the other constructive. The upper parts are eaten away in gorges and amphitheaters until the intervening remnants are reduced to sharp-edged spurs and crests, and all the detritus thus produced is swept outward and downward by the flowing waters and deposited beyond the mouths of the mountain gorges. A large share of it remains at the foot of the mountain mass, being built into a smooth sloping pediment. If the outward flow of water were equal in all directions this pediment would be uniform upon all sides, but there is a principle of concentration involved, whereby rill joins with rill, creek with ™ Journal Geological Sener of London, Vol. XXIX, 1873, pp. 441-471, Second Annual Report U. S. Geological Survey, p. 183 et seq. 256 GEOLOGICAL HISTORY OF LAKE LAHONTAN. creek, and gorge with gorge, so that then when the water leaves the margin of the rocky mass it is always united into a comparatively small number of streams, and itis by these that the entire volume of detritus is discharged. About the mouth of each gorge a symmetric heap of alluvium is produced, a conical mass, of low slope, descending equally in all directions from the point of issue, and the base of each mountain exhibits a series of such allu- vial cones, each with its apex at the mouth of a gorge, and with its broad base resting upon the adjacent plain or valley. Rarely these cones stand so far apart as to be completely individual and distinct, but usually the parent gorges are so thickly set along the mountain front that the cones are more or less united, and give to the contours of the mountain base a scal- loped outline.” In the Lahontan basin alluvial cones are to be seen everywhere about the bases of the mountains, and were evidently a conspicuous feature in the pre-Lahontan topography, as is abundantly illustrated by the fact that the shore lines of the former lake are traceable for hundreds of miles on alluvial slopes of great magnitude. This is particularly noticeable in the northern portion of the basin where the lake was generally shallow, and may be observed especially in the Humboldt and Quinn River valleys and about the bases of the Slumbering Hills. The same phenomenon is also conspicuous about the borders of the Carson Desert and in Buffalo Spring, Alkali and Mason valleys, as well as at many places on the borders of Walker Lake Valley. These alluvial slopes streaming down from the mountains to a horizon far below the old beach lines, bear evidence that the valleys were deeply filled with alluvium before they were occupied by the Quaternary lake. Since many of these basins never overflowed, it is evident that the alluvial slopes were formed during a time of desiccation when evaporation equaled or exceeded precipitation. If this had not been . the case, it is manifest that lakes would have been formed and the débris filling their basins arranged in stratified beds or built into bars and em- bankments. A large number of valleys in the northern part of the Great Basin which held inclosed Quaternary lakes have been explored, and in each instance the same relation of shore terraces to previously formed alluvial slopes has been observed. It is therefore considered as proven teal SUB-ABRIAL ALLUVIATION. AE | that an arid climate prevailed for a long time previous to the existence of the Quaternary lakes, the records of which are now observable. The rate at which alluvial cones are formed is irregular and depends on a number of variable factors, as, for example, the amount of precipitation, the grade of the canons, character of the rock forming the mountain, etc. As the geological and topographical conditions at a definite locality may be con- sidered constant, so far as the present discussion is concerned, it is evident that alluvial cones are in some manner a record of rainfall. Many obser- vations have shown that they are usually formed in arid regions, and result from sudden storms which flush the canons and sweep out the accumulated débris with violence. This is observable not only during the occasional “cloud bursts,” as the sudden storms of the Far West are called, but may also be inferred from the occurrence of angular rocks, weighing many tons, on the surfaces of the alluvial cones. During the intervals between the storms, disintegration takes place in the uplands, and the smaller tributaries deposit their loads in the larger canons, which thus become charged with débris. ‘The rapid deposition of alluvium about the mouths of canons is largely influenced by the fact that what was entirely a surface stream during its canon course, smks below the surface on passing to the alluvial slope and deposits its load. These considerations might be extended and the action of perennial streams contrasted with the results produced by infrequent storms, but perhaps enough has already been written to show that alluvial cones are not only characteristic of arid climates but that the precipitation which produced them is commonly paroxysmal. Thereis mani- festly no uniform rate at which subaérial alluviation takes place and no definite measure of the time necessary for the accumulation of débris of this character, but the comparative size of the deposits made during distinct periods furnishes at least a general indication of the relative length of time required for their accumulation Assuming that the conditions of alluviation were equally favorable during the pre-Lahontan and recent arid periods, we may determine from the magnitude of the subaérial deposits in each instance the relative dura- tion of the two periods. The Lahontan terraces carved on the slopes of ancient alluvial cones are but delicate inscriptions which, in a geological Mon. xI——17 258 GEOLOGICAL HISTORY OF LAKE LAHONTAN. sense, are extremely ephemeral, yet they are clearly legible at the present day, thus indicating the recency of their origin. The time that the terraces have been exposed to subaérial erosion must evidently be extremely brief in comparison to the ages required for the accumulation of the vast debris piles on which they were made. Another, although less definite proof of the aridity of the time preced- ing the rise of Lake Lahontan is furnished by the canons of the streams that enter the basin. In many instances these were excavated to their present depth before the existence of the lake, which subsequently occupied their channels for many miles. An illustration of this phenomenon is fur- nished by the canons of Smoke and Buffalo creeks, which were eroded to the depth of 250 or 300 feet through compact basalt before the rise of Lake Lahontan. When the lake had its greatest extension it occupied the lower portions of these gorges and filled them deeply with marly-clays and delta deposits, at the same time that their walls became loaded with tufa. When the lake retired the streams reclaimed their ancient channels and com- menced the removal of the lacustral strata. The creeks are now flowing over their ancient beds of basalt, but the recent corrasion of the volcanic rock is scarcely perceptible. The amount by which the canons have been deepened during the present arid period, as compared with the work accom- plished in pre-Lahontan times, is certainly in the proportion of one to many thousand. Parallel illustrations of the same phenomena are furnished by the rivers which enter the basin from the west, all of which flow in channels of pre-Lahontan date, and became partially filled with lacustrine strata and subsequently re-excavated as in the previous instances. Each of these streams now flows through a canon within a canon, in the manner illus- trated by the diagram on page 44. It might be said that when these cations were formed, the basin to which they are now tributary had a free drainage to the sea. It is impos- sible to prove or disprove this hypothesis, but in general, canons of the character of those in question may be considered as characteristic of arid regions. Besides, we know, from the great depth of marl and gravel in many of the valleys of the Great Basin, that they have been regions of accumulation for long periods. The weight of evidence is such, in our HUMIDITY OF THE QUATERNARY. 259 judgment, as to confirm the hypothesis that an arid period of long dura- tion preceded the first rise of Lake Lahontan of which we have definite knowledge. The variations and fluctuations of the pre-Lahontan arid period are unknown, but, from the general teachings of meteorology, we may reason- ably conclude that, like the present climate of the Great Basin, it was marked by many fluctuations in precipitation and evaporation, which at times gave origin to lakes of greater or less extent. As the arid period drew to a close and more humid conditions prevailed, it is most reasonable to suppose that the change was gradual. The phenomena do not call fora sudden break in the processes of nature. Humidity of the Lahontan period.—Inclosed lakes may be considered as representing the net balance between precipitation and evaporation. As the relations of these two climatic elements are complex and independent, their resultant will be inconstant and variable; their mutual neutralization, so far as the lakes of a region are concerned, must, therefore, be a matter of delicate adjustment. It follows from this that the difference in climate between a time of expanded lakes and a time of desiccation might be com- paratively moderate. In a given area, like the Great Basin, we may safely say that a lower- ing of the mean annual temperature will increase precipitation and decrease evaporation, thus affording the climatic conditions favorable to the expan- sion of the lakes. On the other hand, a rise in the mean annual tempera- ture would increase evaporation and decrease precipitation, thus favoring the contraction and extinction of inclosed lakes. The existence of a large number of lakes in the Great Basin during the Quaternary is seemingly good evidence that the climate of the region during the time of their greater expansion was more humid than at present; unless it can be shown that there was a very great decrease of evaporation without a corresponding increase of precipitation, a phenomenon only to be observed at the present time in the arctic latitudes. That many of the lakes did not overflow is equally positive evidence that precipitation within their hydrographic basins could not have been excessive. Had the rainfall been even moderately copious, it seems. self- 260 GEOLOGICAL HISTORY OF LAKE LAHONTAN. evident that the entire Great Basin must have become tributary to the ocean. Inclosed lakes of the present time are located in arid regions. The lakes of humid regions invariably overflow. In arid countries the water surfaces of the lakes are small in comparison to the areas that they drain; in humid regions the reverse is the rule. Lake Lahontan, as previ- ously stated, was 8,422 square miles in area, and drained a region over 40,000 square miles in extent; the water surface of the basin at the pres- ent time is approximately 1,500 square miles. The Quaternary lake dur- ing its maximum, occupied approximately one-fifth of its hydographie basin; at the present time only about one-twenty-sixth of the same area is covered by water. From these data alone it will be seen that the present is a time of desiccation in comparison to certain portions of the Quaternary. Comparing Lake Lahontan with existing lakes in humid regions, we find that its water surface was small in reference to its drainage area. In the case of Lake Superior, for example, the area of the lake is to the area of its hydrographic basin as 1 to 1.72. The combined areas of the Lau- rentian lakes is to their combined drainage areas as 1 to 3.19." Could the Laurentian lakes be inclosed, so that the only escape for their waters would be by evaporation, it is evident that they would expand and occipy a vastly larger part of their drainage areas than at present. In fact, the mean annual evaporation in this region is-much less than the mean annual rainfall, so that an inclosed lake would be an impossibility.” ‘In obtaining the data given above, the following table was compiled, which we insert for conyen- ience of reference. Areas of lakes and of their hydrographic basins. Lakes. | Water areas. Hydrographic a wares | Ne graphic area. | — | = Square miles. | Square miles. | Superior’. ~<.202 S222 seacer sane sceceseee sees 30, 829 84, 961 Michigan (including Green Bay) ---.-.--..-- } Pa Bly be ee ra ts Huron (including Northwest Passage 1,556, and! Georgian Ba9.5'626) en ete | PP 7 | (ees, op tems aes Saint! @lain too. fenca~ pane = ee Re eos OBG i seeeeerstteer a2 1 Oy aoe ae Aen Ne ae Pe ian rye Oo a OFGaa7 [eee Ontario ttssceceee teeth eee ae oko eee 730) O45 chee eens ser (Combined) areas aos os eee ee “93, 733 | 299, 919 1to 3.19 | Bonnovilloee: ses. eee see eee | 19, 750 52, 00 | 1 to 2.63 | ® Ann. Rep. Chief of Engineers, U. 8. A., 1869, pp. 645-648. HUMIDITY OF THE QUATERNARY. 261 Considerations of this character might be multiplied, but it is presumed that enough has already been written to show that the climatic change which gave origin to Lake Lahontan but did not permit it to overflow, must have been one of moderate precipitation in comparison, for example, with the present rainfall of the region of the Laurentian lakes, even if we consider the rate of evaporation in the Great Basin to have been the same during the Quaternary as now. An increase in the annual rainfall of a region may safely be considered as causing a decrease in the mean evaporation, thus indicating that the rainfall in the region of Lake Lahontan during the Qua- ternary, could not have been greatly in excess of the present mean annual precipitation in the same area. It will be seen from this that the his- tory of Lake Lahontan is decidedly in opposition to the hypothesis that the climate of the Glacial epoch was characterized by a marked increase in precipitation. A safe conclusion seems to be that the change from arid to more humid conditions which produced the Quaternary lakes of the Great Basin was not sudden or excessive, but consisted in gradual climatic oscillations of moder- ate range. Considering the question of humidity alone, we venture to correlate periods of lake expansion with an increase in mean annual precipitation; and periods of contraction and desiccation with decrease of rainfall We therefore use the diagram representing the fluctuations of Lake Lahontan, as an expression of the humidity element in the climate of the region during the Quaternary. Interpreting the curve representing the oscillations of the lake in terms of humidity we have: Humid Period. Humid Period. Inter-Lahontan Dry Period, Post-Lahontan Dry Period. Pre-Lahontan Dry Period. Fie. 34.—Curve of Lahontan climate. Wet versus dry. 262 GEOLOGICAL HISTORY OF LAKE LAHONTAN. Temperature of the Lahontan Period—Considering temperature as the controlling climatic element—in reference to a restricted region, as in the preceding discussion—and knowing that a high temperature promotes evap- oration and hence tends to decrease the volume of lakes, and that a low temperature produces a contrary result, we should apparently be justified in concluding that as the Quaternary lakes of the Great Basin were larger than the present water-bodies of the same region, the former climate must have been colder than the present. It may be said, however, that had the cold been intense and produced arctic conditions, precipitation would have been retarded. This postulate, however, is not applicable to the area in question, where the climatic oscillations were of moderate intensity even in compari- son with the present prevailing arid conditions, thus indicating that if the periods of desiccation were times of arctic cold, the lake periods must have been at least sub-arctic. On this assumption the Great Basin to-day should have a climate resembling that of cireumpolar lands. The absence of ‘ice walls” about the smaller of the Quaternary lakes of the Far West is nega- tive evidence, perhaps of some value, in opposition to the above hypothesis, Moreover, the character of the abundant molluscan fauna of the Lahontan basin precludes the hypothesis of an arctic climate. If we postulate sub-tropical or tropical conditions of the Lahontan ba- sin during the Quaternary, we must, from the analogy of tropical countries in general, conclude that the region would probably have been humid as well as warm, and consequently productive of abundant faunas and floras. The absence of fossils indicative of such conditions is sufficient evidence that they did not prevail. In the chapter devoted to the life history of the former lake it has been shown that its shores must have been at least as desolate and lifeless as the borders of the existing lakes of the same region. The alternation of humid and arid conditions during the Quaternary finds, perhaps, its best analogue in the present annual climatic changes of the same region. The seasons in the Great Basin are two, an arid and a humid, the former being of the greater length. In the winter precipitation is abundant in comparison with the summer; in fact nearly the entire rain- fall of the year takes place between December and March. During these months the skies are clouded, and rain and snow are not infrequent; the TEMPERATURE OF THE QUATERNARY. 263 rivers rise, and many channels that are completely dry during the summer become flooded; the inclosed lakes increase in area and many new ones are formed in basins that are parched deserts during the summer months. The winter season is, therefore, the humid period, during which evaporation is decreased, and is in every way favorable to the existence of lakes. Could these conditions be continued for a sufficient length of time each year it is evident that the Quaternary lake basin would be refilled. On the other hand, thronghout the arid season the rain ceases almost entirely, the skies are clear and cloudless for days and perhaps weeks at a time; the heat in the desert valleys becomes intense, and evaporation is greatly accelerated. The result is a decrease and failure of the streams and the shrinkage and disappearance of the lakes. These annual changes illus- trate the character of the secular oscillations that took place during the Quaternary. The former great extension of the lakes of the Great Basin is, there- fore, considered as evidence that the mean annual temperature was then lower than at present. Interpreting the curve given on page 237, which indicates the fluctuations of the Lake Lahontan, in terms of temperature we have the following as a generalized diagram of this element in the climate of the Quaternary: : 3 3 3 5 $ a o o a. Cold Period. e Cold Period. £ E 3 5 EB = > = c ¢ c = £ Ss c Fs 5 = 2 = 4 =| L b 2 2 o PLL Se aan ee eee = — (SS Se 2 pont Seat? ‘ vA s , Fia. 35.—Curve of Lahontan climate. Cold versus warm. In the last few pages of this attempt to decipher the prevailing ehar- acteristics of the climate of the Quaternary in the region of Lake Lahontan, the questions of humidity and temperature have been considered in refer- ence to a restricted area. In treating of such a complicated and far-reaching question, however, it is evident that we should not be confined by geograph- ical limits, but must count the changes of climate in broad and perhaps far- 264 GEOLOGICAL HISTORY OF LAKE LAHONTAN. distant regions. In fact, a study of the climate of a given region, to be complete, must contemplate the atmospheric phenomena of the world. Nei- ther can we postulate an alteration of a single element in the climatic envi- ronment of a region without altering the relations of all the remaining ele- ments. Hence the interpretation of geological records in terms of climate become more and more difficult. Our conclusions, therefore, in reference to the climate of the Quater- nary are at the best somewhat arbitrary and are open to controversy. The weight of evidence and the impressions which one receives from the study the phenomena in question are such as to lead to at least a well-grounded opinion, even if some of the facts observed might be interpreted differently by different observers. The present arid climate of the Great Basin cannot be explained by saying that the temperature is high and consequently the water that is precipitated is rapidly evaporated. On the contrary, evaporation is rapid, probably for the reason that precipitation is moderate, or, perhaps more accu- rately, because the mean annual humidity of the atmosphere is low. In explanation of the present aridity some writers have attempted to show that as the prevailing winds blow from the Pacific, and consequently are obliged to cross the Sierra Nevada before reaching the Great Basin, the mountains condense their moisture, and hence they reach the region to the eastward as drying winds. In this explanation it is forgotten that the Sierra Nevada is scarcely, if at all, more humid than the Wasatch or some of the higher of the basin ranges, and that much of the Pacific slope is also an arid coun- try, although situated between the ocean and the mountains that are sup- posed to rob the winds of their moisture. Other explanations of the aridity of much of the region west of the Rocky Mountains have been advanced, but it remained for Captain Dutton to present the view that apparently has the strongest foundation.” This writer explains the aridity by peculiarities of the currents of the Pacific. In brief, this theory assumes that the cur- rents from the north which follow the western border of the continent cool the air that is carried over them towards the land, this being the prevailing direction of the air currents of the region; consequently, on reaching the 83 American Journal of Science, Vol. XXII, 1881, pp. 247-250. GLACIERS AND CLIMA'TIC OSCILLATIONS. 269 land, the air has its temperature increased, and thus becomes a dry wind. If this explanation of the present climatic condition of the Great Basin be accepted, it is evident that past fluctuations in the -climate of the same region could be accounted for by assuming changes of direction in the cur- rents of the Pacific. Testimony of the Glaciers—Thus far our discussion has been confined to the evidence afforded by the records of the ancient lakes. It is mani- fest that the glaciers which existed on the neighboring mountains during the time the lakes were flooded should furnish additional evidence bearing on the same question. The climatic conditions favoring the origin and growth of glaciers has recently been a subject of controversy. Some writers have claimed that the Glacial epoch was a warm period, in comparison with the present, and that the extension of the glaciers was due to an increase of precipitation caused by a greater evaporation over distant oceanic surfaces, the increased evaporation being caused by a general rise of the mean annual temperature. This hypothesis, we believe, was first suggested by Tyndall and Frank- land, and has been extended by Professor Whitney in his work on “Climatic Changes in Later Geological Times.” A number of articles in various scien- tific journals have also been published in extension and support of the same assumption. It is beyond the scope of the present volume to enter into the theoret- ical discussion thus opened, nor is it necessary, as the arguments brought forward by the writers cited above have been controverted by Newberry, Dutton, Gilbert, and others, who adhere to what may be called the ortho- dox belief—having been held by the majority of writers on geological climate—that glaciers are an index of cold, and that their great increase during the Quaternary was due to a decrease in mean annual temperature. In other words, the winters during the Glacial epoch were longer or more severe than at present, and their snows not completely melted during the short summers. The conclusions reached by these writers is so entirely in accordance with all that has come under our own observation in reference to the existence of glaciers, that we do not hesitate in considering their de- terminations as final. The fact that the winter season in the Far West, for example, is the one that favors the accumulation of snow and the growth of 266 GEOLOGICAL HISTORY OF LAKE LAHONTAN. glaciers, while during the summer these conditions are reversed, seems enough in itself to show that an extension of the winter conditions, from whatever cause, for a greater portion of the year would favor the extension of the present glaciers and the formation of new ones, as well as the increase of the existing lakes and the flooding of valleys that are now arid through- out the year. Prolonging the winter conditions in temperate latitudes would therefore initiate a glacial epoch. This is the more evident as the climatic change necessary to cause an extension of the existing glaciers of the Sierra Nevada so as to approximate to their former magnitude, or the growth of the existing lakes of the Great Basin until they equaled the extent of the Quaternary water surface of the same region, need not be considered as a climatic change of great intensity. There are no records of the former existence of glaciers within the basin of Lake Lahontan, but the western border of its hydrographic basin was once buried beneath a vast accumulation of snow and ice that covered all the higher portions of the Sierra Nevada. The Kast Humboldt range, which forms a portion of the eastern border of the same drainage area, was also glacier-crowned. In the central portion of the basin, the Sho- shone, Star Peak, and Granite ranges rise to an elevation of about 10,000 feet, and are reported by the geologists of the Fortieth Parallel Explora- tion to bear evidence of former glaciation about their summits. . The former presence of extensive glaciers on the Sierra Nevada and Wasatch mountains, and of ice fields of less extent on some of the inter- mediate ranges, is sufficient to prove that during that time all the mountains of the region must have been snow-covered for at least a large portion of each year. This in itself—unless the temperature throughout the year was below freezing—would necessitate the formation of lakes in the inclosed basins between the ranges. In three instances in the Bonneville basin, and at four localities near Mono Lake, the glacial and lake records of Quaternary date overlap. The moraines at the western base of the Wasatch mount- ains which descend below the level of the Bonneville beach have been de- scribed by Mr. Gilbert ;*! in this instance, however, the relative age of the moraines and lake terraces is indefinite. In the Mono basin a number of Second Ann. Rep. U. 8. Geol. Survey, p. 189. FLUCTUATION OF GLACIERS. 267 glaciers of large size formerly flowed down from the High Sierra, which forms its western border, and deposited moraines of great magnitude, on which the terraces of the Quaternary lake, that formerly filled the basin to the depth of nearly 900 feet, are distinctly traced. The moraines at Mono Lake were carried out into the valley as parallel ridges, or morainal embank- ments as we have found it convenient to call them, which in several instances are prolonged for a considerable distance below the highest of the ancient beaches, and have terraces traced not only on their outer slopes but on the inner sides of the couches formerly occupied by glacial ice. In some in- stances deltas have been formed between the extremities of the moraina] embankments. The proof is therefore conclusive that the greatest exten- sion of the glaciers preceded the maximum rise of the lake. How far the glaciers had retreated up the canons before the lake occupied their former beds it is impossible to determine. It has also been found that the glaciers of the Mono basin had two or more periods of maximum extension, sepa- rated by times when the ice withdrew far up the canons through which it flowed. There were at least two well-marked glacial epochs in the Sierra Nevada. The lacustral records of the Mono basin indicate two periods of high water, corresponding, it is presumed, to the two main periods of glacial extension. All the facts known to us are in harmony with the conclusion that the two humid periods recorded in the Bonneville and Lahontan basins were practically synchronous with the two periods of maximum extension of the Sierra Nevada glaciers. The fact that the greatest rise of the Qua- ternary lake occupying Mono Valley occurred after the greatest expansion of the glaciers does not militate against this determination, but indicates that the melting of the snow and ice on the mountains contributed an un- usual supply of water to the lake, which then received its greatest flood. When mountains bordering an inclosed basin are loaded with snow and ice, it is evident that a rise of temperature will cause a flooding of the valleys. The analogy between the glacial climate of the Great Basin and the winter climate of the same region at the present time, thus finds another parallel. The evidence leading to the correlation of the two high-water stages of Lake Lahontan with the two Glacial epochs of the northern hemis- phere has already been indicated. Should this conclusion be sustained, 268 GEOLOGICAL HISTORY OF LAKE LAHONTAN. it follows that both series of phenomena resulted from a common climatic change. In the case of Lake Lahontan we have attempted to demonstrate that the change which caused the expansion of the lake was a lowering in the mean annual temperature, and that the periods of desiccation indicate a relative rise of temperature. This interpretation is in harmony with the verdict of the great majority of writers in reference to the prevailing ele- ments in the climate of the Glacial epoch. In former times, as at present, the climate of various regions in the same latitude differed widely in refer- ence to humidity. The more humid regions were the areas of greatest glaciation. The discussion of the ultimate cause of the cold of the Glacial epoch is beyond the scope of the present report. A summary of the writer’s conclusions in reference to the climatic oseil- lations indicated by the fluctuations of Lake Lahontan is embodied in the following schedule : { Probable Claneticconditions £4 time of aridity; precipitation small; evaporation 1: PrecTatindtan aniaipestoa os | rapid; temperature high. | 5 Lakes smal!, at times desiccated; mountains free from Resultsi-2- oe ss =e i) glaciers. Precipitation moderate; evaporation decreased ; tem- Probable climatic conditions. -- f : perature low. Large lakes in the valleys and glaciers in the mount- ( \ 2. First rise of Lake Lahontan -- { | U ains. IROSUItS see eee eee eee ; Probable climatio conditions. 5 Decreased precipitation ; evaporation rapid; tempera- ¢ ture high. 3. Inter-Lahontan arid period ... Lakes smaller than at present, and at times possibly Reguligc ee eae eee desiccated; glaciers contracted and possibly com- (pletely melted. ¢ Precipitation moderate, but probably more copious than H during the first rise; evaporation decreased ; temper- ature low. ( Probable climatic conditions. -- | 4. Second rise of Lake Lahontan. { | UResultsno pec on necem-cenenae ne Broad lakes and large glaciers. A time of great aridity; precipitation small; mean Probable climatic conditions. .. : temperature higher than at present. . Post-Lahontan arid period ..-. i ct JOS esse soconcseass ses Lakes desiccated and glaciers melted. Olimintiolconditions eee fPrceiptiation small; evaporation rapid; mean temper- ature about 50° Fahr. 6. Present time ........-.-..----- { een arid; rivers small and fluctuating ; lakes and Results 'e son sn sawn cic ce dosniese glaciers small. CCAP Phy REX. GEOLOGICAL AGE. OF LAKE LAHONTAN. A review of the facts bearing on the age of Lake Lahontan necessi- tates some repetition, but seems desirable in order to present the evidence in a connected form. The reader is already aware that Bonneville and Lahontan were the largest of an extensive series of lakes which formerly occupied the valleys of the Great Basin. That the lakes here indicated—represented for conve- nience of reference on Plate I—were contemporaneous seems too positive to be questioned. The records in the various basins are identical, consist- ing of terraces, gravel embankments, sedimentary deposits, fossils, ete., in which no difference of age can be detected. Moreover, the existence of lakes in inclosed basins is dependent on climatic changes too broad in their effect to have been felt in a single valley without producing similar results in others near at hand That the lakes now under discussion, not only existed at the same time, but were also of a very recent date, is considered as abundantly proven by the fact that they left the very latest of all the completed geological records to be observed in the Great Basin, The fossil shells obtained from the sediments and tufas of Bonneville and Lahontan, and a few of the smaller sister lakes, all belong to living species. The mammalian remains discovered in the sediments of Lake La- hontan are the same as occur elsewhere in Tertiary and Quaternary strata. The spear head of chipped obsidian obtained in the upper Lahontan sedi- ments is considered good evidence—although as yet unsustained by other finds of a similar character—that man inhabited this continent during the last great rise of the former lake.’ 269 270 GEOLOGICAL HISTORY OF LAKE LAHONTAN, The greatest expansion of the waters of the Mono basin, occurred sub- sequent te the last extension of the Sierra Nevada glaciers. Although this is the only instance known where the relation of the former lakes and gla- ciers of the Great Basin is clearly determinable, yet it seems a necessary inference that the other lakes of the same region attained their maximum at the same time. As the formation of glaciers and the extension of lakes in inclosed basins necessarily result from similar climatic changes, we corre late the two flood periods of Lake Lahontan with the two periods of maxi- mum extension of the Sierra Nevada glaciers. Again, from similarity of phenomena, the two periods of glaciation on the mountains of the Far West, are correlated in time with the two glacial epochs of northeastern America, as recognized by certain geologists. If this determination is correct, it fol- lows that the last great expansion of the lakes of the Great Basin occurred during the close of the Glacial period, and may be considered as contem- poraneous with the Champlain epoch of the eastern States. | That the valleys of the Great Basin held lakes, at least at intervals, throughout the Quaternary, is not only probable, @ priori, but is indicated by the great thickness of marls, clays and gravels that fill these depressions. In the Bonneville basin these deposits have been penetrated to a depth of over 1,500 feet without reaching the underlying rock. That the lower portion of the material filling these depressions may be of Tertiary age, is certainly possible, but the records of the passage of the Tertiary into the Quaternary are so obscure and so little known that it is at present impossi- ble, at least in the lake-beds of the Far West, to say where the former ends and the latter begins. When Lake Lahontan began its existence will prob- ably never be known, except in a general way; but that it reached its greatest extension in late Quaternary times and was approximately synchro- nous in its fluctuations with the advance and retreat of the Sierra Nevada glaciers during the Glacial epoch is a fair deduction from the evidence re- corded in the present volume. In regard to the time, as measured in years, that has elapsed since the events described in this report took place, we have but shadowy evidence to offer. It has been estimated by James Croll,” from astronomical data, that % Climate and Time, New York, 1875. Chap. XIX. DATE OF THE GLACIAL EPOCH. 271 the last Glacial epoch terminated about 80,000 years ago. Other investigators have approached the problem in different ways and reached widely discor- dant results. At present even an approximate measurement in years of the time that has elapsed since the last great retreat of the glaciers of the north- ern hemisphere seems impossible. Considering that Lake Lahontan fluc- tuated synchronously with the advance and retreat of the glaciers during the Glacial epoch, we must conclude that its last evaporation followed the last great retreat of the glaciers. Our studies in the Far West have shown that there is no reason for supposing that the retreat of the Sierra Nevada glaciers was a sudden event, partaking of the nature of a catastrophe, or that the evaporation of the lakes which were supplied by the melting ice, was a matter of a few years. On the contrary, the glaciers are believed to have retreated slowly; with many pauses, and the evaporation of the lakes to have extended through centuries. Even if the Glacial epoch can be proven to have terminated 80,000 years ago, there is no reason for consid- ering that desiccation of the lakes followed that event within many thou- sand years. As stated at the beginning of this paragraph, we have no defi- nite evidence to show that the Quaternary lakes were flooded a certain number of years since; but one familiar with the shore phenomena displayed in the valleys of the Far West cannot fail to be impressed with the perfec- tion with which these structures have been preserved. In many instances the embankments of gravel are as perfect in contour and as regular in slope as if constructed but a few years ago. Subaérial erosion is reduced to a minimum in such instances, however, for the reason that the structures are porous and absorb nearly all the rain that falls upon them, allowing it to percolate quietly through their interstices. Changes of temperature have but little power to alter their forms, owing to the large size of the inter- spaces and the readiness with which moisture is removed. The only ele- ments of subaérial erosion to which gravel embankments seem open to attack are the wind and the beating of rain During the lapse of centuries even these slow processes must effect appreciable changes, but as yet this is scarcely apparent in the embankments built in Lake Lahontan. It is evi- dent that gravel embankments in arid regions, so situated that they are not within the reach of stream erosion, may be considered among the most per- 2ie, GEOLOGICAL HISTORY OF LAKE LAHONTAN. manent of topographic forms; more constant, in fact, than the rocky mount- ain tops. It is not surprising, therefore, that the gravel structures fail to give evidence as to their age. We might consult the canons carved through Lahontan sediments since the recession of the lake fora time measure; but the amount of erosion here apparent could have been performed by the existing streams in a few years, owing to the unconsolidated character of the strata and the high grade of the streams caused by the lowering of their base level upon the withdrawal of the lake waters. Moreover the streams have meandered but little within their canons, thus indicating that these trenches have not been long finished. On the whole the canons indicate that but a brief period has elapsed since their excavation began. The tufa deposits of the basin have been exposed to erosion since the withdrawal of the lake waters, and might be expected to present some indi- cation of the time they had been subjected to subaérial erosion. These deposits are porous and open in structure and favor the absorption and retention of moisture. They are thus especially liable to the destructive effects incident to the freezing of water in the interspaces of rocks, espe- cially as the rains and frosts of the Great Basin occur together. We may, therefore, expect that the subaérial erosion of the tufa deposits would be rapid, and that if they had been exposed for a long period they would exhibit marked evidence of waste and decay. The fact is, on the contrary, that these deposits are remarkably well preserved. The greater amount of fracture and displacement that has been observed has evidently resulted from the weight of the deposits when left unsupported by the waters in which they were formed. The only conclusion to be drawn from the tufa deposits in reference to the date of the last desiccation of Lake Lahontan is that their time of exposure has been short. Again, in reference to the shells strewn over many portions of the deserts which, in many cases, must have been left by the evaporation of the former lake, we find that these fossils, or semi-fossils, as they have been termed, are bleached white and have lost their epidermis, but are otherwise frequently as perfect as when inhabited by the mollusk to which they belonged. ‘That these fragile bodies have been drifting about at the caprice DATE OF THE QUATERNARY LAKES. 273 of the winds for thousands of years without being destroyed is improbable, to say the least. Other facts bearing on the determination of the length of time that has elapsed since the close of the Glacial epoch may be observed in the canons of the High Sierra, and have been described in part in a previous essay.” We need not consult the moraines left by the ancient glaciers, as these, like the gravel embankments mentioned above, are comparatively stable struct- ures; but in the glaciated canons there are numerous bosses and domes of granite and quartzite that have been exposed to the sky since the glacial ice was melted from above them. The ice-polish on these ledges is still conspicuous, and causes them to glisten in the sunlight as brilliantly as do similar surfaces adjacent to the existing glaciers of the High Sierra and of Switzerland. These smooth surfaces are still scored with fine hair-like lines, and the eye fails to detect more than a trace of disintegration that has taken place since the surfaces received their polish and striations. Here again we meet with the difficulty of applying quantitative measurements; but as there is a limit to the time that rock surfaces may retain their polish it seems reasonable to conclude that in a severe climate like that of the High Sierra it could not remain unimpaired for more than a few centuries at most. The cumulative weight of these various lines of inquiry is such as to lead to the opinion that the last desiccation of the Quaternary lakes of the Great Basin certainly occurred centuries but probably not many thou- sands of years ago. On the other hand, it might be argued that the pres- ence of the bones of the mastodon, camel, and horse in the lacustral clays, deposited during the last great rise of the lake, is abundant evidence of the antiquity of thatevent. ‘The date of the various fluctuations of Lake Lahon- tan, as measured by the standard used in human history, thus remains an open question. % Existing Glaciers of the United States, Fifth Annual Report U. S. Geological Survey. Mon. xt 18 CHA PVE R, XX: POST-LAHONTAN OROGRAPHIC MOVEMENTS. In our sketch of the origin of the Lahontan basin (ante, page 24), a brief account of the pre-Quaternary faults of the region was given. As there stated, the area we are studying has been broken by profound frac- tures, which resulted in the division of the rocks into a great number of orographie blocks. The unequal displacement of these gave origin to the various valleys that were occupied by the Quaternary lake. In the present chapter we wish to direct attention to similar movements of the earth’s crust which have taken place since the evaporation of Lake Lahontan. The traveler in the Great Basin frequently sees low escarpments in lacustral beds and alluvial slopes, which form irregular lines along the bases of the mountains, and at times cross the valleys. In profile, these scarps present various appearances, as illustrated by the following sections. Where they cross alluvial slopes they usually exhibit a profile similar to that shown at a. In the open valleys they form a small cliff or steep ascent, joining a Fic. 36,—Ideal cross-profiles of faulted beds. horizontal plain below with a similar plain above, as indicated in section atb. Ona mountain side the scarp is usually partially in rock and partially in alluvium, as represented at c. The course of the scarps is always irreg- ular, and sometimes forms zigzag lines that may be followed for many miles. 274 LAKE LAHONTAN PL. XLIV — Julius Bien & Co. Lith. POST - QUATERNARY FAULT LINES. U.S. GEOLOGICAL SURVEY 29 miles «inch Seale hd e a on S 7 . @ « =< + . LS 4.7 } . - P 7 RECENT FAULTS. 27d The scarps differ from the steep slopes bounding water-built terraces and embankments—that neither their upper or lower limits are horizontal for any considerable distance; they are characterized by irregularity, and do not define the boundaries between deposits of different character hey occur both above and below the highest beaches of the Quaternary lakes of the region where they are found, and exist in valleys that have a free drainage as well as in those that are inclosed and once held lakes. It is, therefore, evident that their origin is totally independent of the action of waves and currents, and it is equally clear that they cannot be the result of erosion. Scarps of this nature were first observed in the Great Basin by Mr. Gilbert, while examining the western base of the Wasatch Mountains, and were recognized as the result of recent orographic movements.” In other words, they are fault scarps of very late origin. Their recency is shown by the fact that they commonly occur in Quaternary lacustral sediments and recent alluvial slopes, and form steep slopes of earth and gravel that are but little modified by erosion, and in many instances are bare of vegetation. In many cases, it is evident that they could not have existed in their present condition for more than a few years. Sometimes they are more than a hundred miles in length, and vary from a few feet to more than a hundred feet in height. Recent faults of this nature have been observed along the western base of the Wasatch Mountains, at the eastern base of the Sierra Nevada, and on the foot-slopes of many of the intermediate Basin ranges. In the La- hontan area recent fault scarps are a common feature in the topography of the valleys, and furnish one of the many interesting problems in the physi- cal geology of the region. All of the lines of post-Lahontan displacement that ave actually known to exist in the Lahontan basin are sketched on Plate XLIV, with as much accuracy 28 the topography of the map admits. It is evident that our knowledge of this phenomenon is incomplete, as only the more recent dis- placements are apt to attract attention, for the reason that when erosion has modified the scarps it is frequently impossible to determine whether post- §7Second Annual Report U. $8. Geological Survey, p. 192. 276 GEOLOGICAL HISTORY OF LAKE LAHONTAN. Quaternary movement has taken place or not. Could the full extent of the recent fault lines be indicated on the map, it is probable that they would form a complicated series of intersecting lines that would embrace nearly the entire area. The first feature of general interest that presents itself upon commenc- ing the study of these recent faults, is that they frequently, if not always, follow the courses of ancient displacements that are usually of great magni- tude. They are recent movements of ancient faults. The intimate association of thermal springs with recent faults is to be noticed not only in the basin of Lake Lahontan, but throughout the entire area of interior drainage thus far explored. It is also to be noticed that the hottest springs almost invariably occur on the lines of displacement that have suffered the most recent movement. So nearly constant is this corre- lation, that wherever thermal springs occur, other evidences of recent oro- graphic movement are almost always at hand. The suggestion has been advanced in this connection® that the high temperature of the springs is due to the friction of the rocks along the sides of the fault plane. It is the conversion of motion into heat. As, however, the faults result from a pro- found fracturing of the earth’s crust, it is evident that any water which finds its way into a fault may descend to great depths and consequently reach regions of high temperature; it is more than probable, therefore, that the springs derive at least a portion of their heat from the internal heat of the earth. It is impossible at present to determine how much of the heat affect- ing springs is caused by friction and how much is due to the prevailing high temperature of the earth at great depths. Probably both causes con- spire to produce the results observed. The intimate association of the thermal springs of the Lahontan basin with recent displacements may be illustrated by comparing Plates VII and XLIV, which will show that but a very few thermal springs occur in this area that are not closely associated with recent faults. The various lines of recent displacement in the Lahontan basin have so many features in common that it is unnecessary to enter into a detailed description of each. All that are represented on Plate XLIV, within the % Third Annual Report U. S. Geological Survey, p. 282. O LiINV4a A HL N¢ m SYOHS AHV1 LOTOSWNH 340 + y “~s RECENT FAULTS. 2G borders of the ancient lake, exhibit scarps in lacustral beds and gravel de- posits, and are therefore more recent than the last rise of the lake. The appearance of the fault at the western base of the West Humboldt range is shown on Plate XLV; the point of view being near the southern end of Humboldt Lake. The precipitous mountain face shown in the pic- ture is in reality an ancient fault scarp of grand proportions, which was somewhat eroded before the existence of Lake Lahontan. During the time the lake occupied Humboldt Valley its waves carved a number of terraces along the base of the mountains, which are represented in the sketch, and are familiar to many who have traveled over the Central Pacific Railroad. Between the highest terrace and the shore of the present lake there is an _ irregular line of cliffs—in part obscured by talus slopes—which has been produced by recent orographic movement. This fault scarp is composed principally of cemented gravels of Lahontan age, but in places the rock forming the mountains may be seen beneath the clastic beds. The charac- ter of the section exposed at many localities along this fault is represented in diagram c, Fig. 36. This fault scarp may be traced continuously from the Mopung Hills northward, along the bases of the West Humboldt and Star Peak ranges, to the neighborhood of Winnemucca, a distance of over a hun- dred miles ; its full extent, however, remains to be determined. Throughout the greater part of its course it crosses alluvial slopes, with a fresh scarp from ten to twenty feet, or more, in height, its greatest magnitude being near its southern end. Along the eastern shore of Humboldt Lake it forms a nearly vertical escarpment, fully fifty feet high. At the Mopung Hills it divides into several branches, which may be traced to the border of the Carson Desert, and then become obscured. _ In describing the shore phenomena on the Niter Buttes, a spur of the main range, at the southern end of Humboldt Lake (see ante, page 112), some account was given of sloping terraces, which indicate that orographic movement must have taken place during inter-Lahontan time. We have evidence, therefore, that the fault along the west base of the West Humboldt range attained a great magnitude previous to the existence of Lake Lahon- tan, that it underwent some disturbance during inter-Lahontan time, and 278 GEOLOGICAL HISTORY OF LAKE LAHONTAN. has increased its displacement fully fifty feet since the evaporation of the Quaternary lake. The hot springs at Hot Springs Station, on the Central Pacific Rail- road, occur on a line of recent displacement, which may be followed for a few miles, both north and south, from the present site of the springs. De- posits of extinct springs may be seen for a mile or more north of the present point of outflow, indicating that former openings, through which the springs rose, have been filled by calcareous deposits, thus compelling the waters to find other points of egress along the line of fracture. The recent fault on the east side of the Carson Desert is marked by a _ low searp in alluvium, and a change in the drainage where the displace- ment crosses Alkali Valley. East of Borax Springs, situated in Alkali Valley on the line of fracture, the slope of the desert surface is eastward, and conducts the drainage to the end of the valley where a lake of brine is formed, which on evaporating leaves a deposit of salt of economic import- ance. Alkali Valley is bordered on all sides by precipitous mountains, excepting where it opens into the Carson Desert, and formed a deep bay during the existence of Lake Lahontan. In passing from the Carson Desert into Alkali Valley no change in the nearly level desert surface is noticeable until the line of faulting is reached; the plain then inclines gently eastward as we have described. It is evident that this inclination of the desert surface has taken place in post-Lahontan times, and is due to a slight tilting of the orographie block on which Alkali Valley is iocated. The course of the fault indicated on Plate X LIV, as crossing the north- ern border of Mason Valley, is rendered conspicuous in the topography of the valley bottom by a scarp from ten to twenty feet high in lacustral marls and clays, and by numerous thermal springs. This is probably a continu- ation or a branch of a displacement in Walker River Valley which presents a section of Lahontan sediments fully 150 feet high. In common with the majority of the recent displacement of northern Nevada, both ends of this fault are obscure and indeterminable. What is probably a continuation of the series of disturbances observed in Mason Valley is indicated by a recent scarp along the east base of the Wassuck or Walker Lake range. The influence of this displacement on RECENT FAULTS. 279 the contour of the lake bottom is indicated to some extent by the soundings given on the map forming Plate XV. The lake is deepest in the immediate vicinity of the fault line. It is probable that the direction taken by Walker River on leaving Mason Valley was determined by orographic movement, as it does not fol- low what appears to have been its natural course, but the character of this change is difficult to describe. The former outlet of Mason Valley was through a narrow gorge leading to the Carson River which it entered at a point opposite the site of Camp Churchill. This would probably have been the course taken by the stream when the waters of Lake Lahontan were withdrawn for the last time, had not orographic movement caused a slight change in the slope of the valley and thus deflected the river to the right. This phenomenon will be better understood on consulting the accompany ing pocket map, where the ancient channel leading from Mason Valley to the Carson River is indicated. That portion of the great Sierra Nevada fault which defines the western border of Carson and Eagle valleys has undergone a recent displacement of from ten to thirty feet, as is shown by fresh scarps in earth and gravel, and also by the outflow of heated waters at several localities. The recent scarp in this instance has been followed all the way from near Carson City to beyond Genoa; the full extent of the movement, however, far surpasses these limits. The basin of Lake Tahoe is an orographie valley of the Great Basin type, but is situated at a high altitude in the Sierra Nevada on the border of the interior drainage area. _With the exception of the hot springs at the northern end of the lake, no evidence is known to the writer tending to show that there has been recent orographic movement in its immediate vicinity. The taults along the eastern base of the Pine Forest Mountains; on the western margin of the Black Rock range, from Black Rock point north- ward, and at the northern base of the Harlequin Hills are all marked in the topography of the country by recent scarps that seldom exceed twenty feet in height. At numerous points along these lines of displacement thermal springs come to the surface. 280 GEOLOGICAL HISTORY OF LAKE LAHONTAN. The large group of hot springs near Ward’s ranch, on the western border of the Black Rock Desert, and the group at the east end of Granite Mountain, are both on lines of recent displacement. The fault that crosses the western border of Smoke Creek Desert differs from most others in the Lahontan basin in the fact that it traverses the valley at a considerable distance from the mountains. Its course is marked by numerous thermal springs, and by a low scarp which at times becomes too indistinct to be easily traced. There is but little question that this line of displacement is a continuation of the fault to be seen at Granite Mountain, which apparently comes to view again along the borders of the Black Rock Desert farther northward. The connection between these various frag- mental fault lines has not been traced, and we have represented on Plate XLIV only such portions as have actually been observed. 'The course of this fault across the southern portion of Smoke Creek Desert is indicated by a low and somewhat rounded scarp with a nearly east and west strike. The springs along the fracture irrigate the desert sufficiently to admit of the growth of grasses and desert shrubs which mark its course by a line of verdure through the absolute waste. Farther northward, in the neighbor- hood of Sheep Head Spring, the fault changes its course and becomes nearly north and south in its trend; farther northward, still, it bends more to the eastward, and, finally, near Round Hole Spring it has an approximately east and west strike. Its course is thus nearly crescent-shaped, but it has many more irregularities than we are able to represent on the accompany- ing map. On the line of this fault near Buffalo Springs there are a number of tufa piles rising abruptly from the desert to a height of thirty or forty feet, which exhibit the three varieties of tufa that are characteristic of the Lahontan calcareous precipitates. It is evident that the nuclei of these deposits were formed by subaqueous springs, as described in a previous chapter, thus showing that the fracture along which they are situated must have existed during the time the desert was occupied by the ancient lake. In a few instances the tufa piles situated immediately above the line of fracture have been split from base to summit by a recent orographic move- ment, and are now parted by vertical fissures two or three feet wide, into RECENT FAULTS. 281 which a person can descend a number of feet lower than the surface of the desert. The fault described in the last paragraph is at such a distance from the highlands to the westward that no alluviation has taken place in its neighborhood. There has, therefore, been no transfer of load from one side of the displacement to the other. The thrown side of the fault under- lies the broad desert and was lightened previous to the last fault-movement by the removal of 500 feet of water from its entire surface. It is quite evident, therefore, from the nature of the facts, that the unequal loading of contiguous orographic blocks, which has been assumed as an explanation of fault movements in certain instances, cannot be considered an element in the present example. A fault along the northern side of Honey Lake Valley shows about as great an amount of post-Lahontan movement as any in the basin. In this instance the trend of the fault is irregular, but in general its course is north- west and southeast; its hade is nearly perpendicular, and the recent displace- ment at times exceeds a hundred feet. The thrown block underlies Honey Lake Valley. From the position of the present lake and the direction of drainage in the valley, it seems evident that the mountains between Smoke Creek Desert and Honey Lake Valley must have been upheaved to pro- duce this fault. A similar but more gentle movement of the same mount- ain mass would account for the recent scarp described above which crosses the Smoke Creek Desert. The faults represented on Plate XLIV, to the north of the Lahontan drainage area, are of the same character as those already described, and will require but a word of explanation at this time. The recent displacement on the west side of Surprise Valley, California, has a throw varying from 2() to 50 feet, and may be traced for nearly a hundred miles across alluvial slopes and gravel embankments of Quaternary age. As in numerous other instances, its course is marked by thermal springs, some of which are of high temperature and afford a large volume of water. The fault along the eastern base of the Stein Mountains, Oregon, falls in this same category, and together with other similar displacements 282 GEOLOGICAL HISTORY OF LAKE LAHONTAN. in the same region will be found described briefly in the Fourth Annual Report of the U. 8. Geological Survey.” From the studies of the recent displacements of the Lahontan basin ~ which we have been enabled to make, it seems safe to conclude that these orographic movements are but the continuation of a series which had its beginning long previous to the Quaternary. These movements were in progress during the existence of Lake Lahontan, as indicated by sloping terraces, and no less plainly by tufa deposits along lines of fracture. As shown above, the evidence that these movements have been in progress in very recent times is abundant. The character of the phenomena is such that it is impossible to resist the conclusion that the forces which produced the results described are still in action. Whether the faults have been formed gradually without any marked disturbance, or whether they have been paroxysmal, is not definitely known. That earthquakes are felt from time to time in various parts of the Great Basin, and the results produced by the Owen's Valley earth- quake of 1872, tend to the conclusion that the orographic movements have been paroxysmal in their nature. The Owen’s Valley earthquake, it will be remembered, resulted in the formation of a false scarp of the same character as those we have been describing, which may be traced for a number of miles As reported by Mr. Gilbert, who recently visited Owen’s Valley, the main scarp produced in 1872 varies from 10 to 20 feet in height, hades eastward ata high angle, and agrees in all its features with the similar scarps observed throughout the Great Basin. This is apparently the latest slip in the great Sierra Nevada displacement. In the case of all the recent faults of the Great Basin thus far exam- ined, the movement has been nearly vertical, and but slight crumpling or contortion of the adjacent strata has taken place. A general view of the phenomena presented suggests that in the majority of instances the blocks now forming the mountains have been raised vertically, while those beneath the valleys remained nearly undis- turbed. This hypothesis cannot be sustained by direct proof, however, 89 Pages 449-454, CHARACTERISTICS OF RECENT FAULTS. 283 and meets with apparent opposition in the case of the fault along the western border of Walker Lake. In this instance a depression of the thrown block is indicated by the deepening of the waters of the lake as one approaches the line of displacement. As pointed out by Mr. Gilbert, Great Salt Lake has probably been shifted to the eastward of its normal position by orographic movement, which we may consider, at least in part, as the result of a movement of the great Wasatch fault; thus indicating that the thrown side of the displacement was depressed. By way of a summary of this chapter we may state that the recent faults of the Great Basin have the following characteristics: They are irregular and angular in their course, in reference to both vertical and horizontal planes. They occur most commonly on the steeper side of the basin ranges, and, so far as known, invariably hade toward the valley, i. ¢. the valleys occupy the thrown sides of the displacements. Their scarps occur in alluvium and in lacustral beds, and cut the embank- ments and terraces of Quaternary lakes; many times they present fresh slopes of earth and gravel that are unclothed by vegetation, and but little attected by erosion. Occasionally they cross stream-beds and cause rapids; as is the case where the Wasatch fault crosses American Fork, Utah. At hundreds of localities thermal springs come to the surface along the lines of fracture. In the majority of instances the recent movement has taken place along ancient lines of displacement; the post-Quaternary fault in such cases is but a small fraction of the entire disturbance. — me Te) eee Te poate tis en tage Gah Tt tare eee 12 i eatolgad Si abe oh. shy ae 4 et iy He (te te Ponda AS sie) Be a bi re ee ee co “Bi wy Apetate 3 ae nme i* et vy Abbot, H. L.; on sediments of the Mississippi. --..--.-. Abert Lake, Oregon. - - AMBolian sands Alkali Valley, Sand dunes in , White marl deposits in. ....-. sasdasecyrac 150 Allen, Prof. O. D., Analyses by -..---.-----------.-- 66, 76-78 JME aed 2 pcSbaoesaSnasedsccdeeseessccrbeesossee 49 , White marl deposits near .--.--..-----. 149 PAN NU WViS CONCS eae eae coe w salen ena sees semen oma 255 J AWG) LRU | ene eS eerccnSaeoo ao cecdcoaee Eosse doses 59, 66 PROXY ACES OU tee see omnes a eal 104, 193 AING I, Caer ceeccaccocas cesetioed 195-196 Analyses of brine of Buffalo Springs Salt Works. -...-.-. 233 brine of Eagle Salt Works .----.....------- 234 GUIDMETCENOES) | Sosecoc eben gress aoeseene 68, 231 European river waters....-....-------.---- 174 GayINBBIte ee ee eccemines eenaneaaateniacsr as 76-77 hot spring, Hot Spring Station, Nevada.... 49 Humboldt Lake water .......--..-..--.---- 67 Humboldt River water........-----.----.-- 41 Lahontan lacustral sediments 128 lakesand rivers of Lahontan basin. ---.-.--- 225 ocean waters Epa eee eatos ao eesmceescsenccs he pumiceous rhyolite - ........--..-----------. 147 Pyramid Lake water .........-..---------. 57-58 TENG EA 8) eS OsO DERG COCOONS EEISES Ee) Ox 174 Rockbridge Alum Spring ---.-.------------ 177 Schaffer’s Spring, Honey Lake Valley. ----- 51 soda from Soda Lakes, Nevada. ...-..-.----. 78 Soda Lake water...-......-...-------..-- = tus South Carson Lake water....--. --. ------ 69 spring waters ...-.------ Truckee River water. - tufa waters of Lake Tahoe ---- 42 Se GERI eee ee tele ees ewe. SEE er iene Gaaua vee ee mea ae seas ia , White marl deposits near. ..-...-.--.--- ULTEM GAT LAGS Mee amet onl =e eee eect nce ome t : 9 . Le Conte, Prof. John; on Lake Tahoe.-..--....-- eal Cuater ag era i erie Caio elec Aen ae vane of Bake Gabon ben on ro of King, Upper and Lower. aonoS 144-145 ROU AND oO CE Rage aaah gr ar = POV ar yO) NWF seme esd t oe = ec OSC OSE COCs 30 ee aoe ie Valley, Sand stones shen a Ser 5 Question of outlet of Lake Lahontan...-......--.--.--. 27-35 2 ee, Pen. S... pik, Foe of eae vats) 2 ? , 142, 2 (ATI Gia ssa, coed seeccoh ave ath Seema o-Goee Sues 41 Madeline Plains, Ancient lake of. Ragtown, Soda Lakes near ........-.....-.------------- 73 STATE IEE eH Ramsay, Prof. A. C.; on color of lacustral sediments. .-.. 169 Mian amine Q\paiernary Ricksecker, Eugene, Aid of -.--. i Marble Buttes, Tufa from .-.. Margaritana margaritifera..-. Marl, White iicecd cette soo ee ane aa ee jee eapeDeEesOeeeS 138, 141 Merel; method of fractional crystallization. --- Mill City, Nevada, Sections near MIBSIREID DIB DANG Usenee mere ane eee sane ae aia sae se aos Mollusks of Pyramid Lake Lahentan basin.....!..-.2--.---.-. 2-26. iWialkerbake)nnoccos sss o- ene can Ls on the shore of South Carson Lake. -- --- 69 Mono basin, Ancient glaciers of ...-....--..-.-.-.-- 266-267 , Contorted stratain..................-... 160, 161 7 exploration Of 22-22-20: Polen T tei p ; ay vila ‘ ‘ Ay j r 4 ce y kp Ae al 5 ‘ A : An. 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