| Summary: | "The monuments of the Ice Age in the Great Basin have been greatly obscured and broken, many of the more ancient of them having perished altogether . in a great part [due] to the perishable character of the rocks of which they were made."" Muir relates in detail the great amount of evidence he has discovered of a past glacial history, describing the gradual but orderly transition from an elevated tableland through various forms, from ""a slow dessication and decay to present conditions of sage and sand."" iduxing 'snow. The.„uul, j -.made-up of irregular volcanic table?, the i extensive, of-which, is about, two .uu. 4= miles long, and like the smaller ones is broken Kjbraptfy down on the edges by the action" ,of. !Peice- Its m>-ht is approximately 11,300 feet hffi-n-Fafis?. Sonffi^oeESeTn: the "Si<- ' > MoantaiESJsrere loaded wuh. glaciers that "<•- . f-scVoded. to. the adjacent valleys during *•*= a] glacial period, and that if is. to'.' tea Francisco. Thursday, Deer^ GLACIAL PHENOMENA 1H NEVADA,. .^SiSreatingDiscoveries by Jolin Muir item iclal fracM—Lateral MoraInee,.Ho**~rile^ Yallejs Were Formed. /' i£.A, %^'f»BCril CORRESPONDENCE OF THE BnLLETIK.J . Utjreka, Nev., November 28,187S.':: muments of the Ice- "Basin, have been greatlj obscured: a many ot the more ancient of them having: gfe|| Ished altogether, leaving scarce a mark o£ thejr? —"existence, however faint; a condition otjiDlngjjL due not alone to the long continued action "of- '.-^ost-glacial agents, but also »great part, to the I perishable character of the rocks of which they ■ wersroad'e. The bottoms of the main valleys, once grooved and' planished like the glacier - pavements of the Sierra, lie buried beneath sedi' .:- meats'anil-detritus derived from the adjacent f meuatains," and now form the arid sage plains ■'. characteristic ^shaped canyons have become : T-H&geattrj- the deepening of their bottoms ar-j. -frsjghtening of their sides, decaying , .glacier aeadlands have been undermined and thrown down in loose talnses, while most of the moraines and striae and scratches have been •-•' Waited- or7 weathered away. Nevertheless, enough remains of the more recent and more er4tmng. phenomena to cast a good Tight well DacJ?"npon the conditions of the aneient ice sifeel'that. covered this interesting region, and u^^fthe system of dissbict glaciers that loaded 'EVIDENCES OF GLACIAL ACTION. " few days after maKing these interesting discoveries, 1 found other well pres«rved glacial s on Are Dome, the culminating summit of} Tciyabe, Bange. On US northeastern-' lopes there are two small glacieriakesv anoV- • the basins of two others -which have recently i been filled with downwashed detritus. One i smalr-residuaLglacier lingered until quite recently beneath the coolest shadows of the dome, • fhe moraines and neve-f ountaina of which are still as fresh and unwasted a3 many of those lying at the same elevation on the Sierra—10,000 feet—while older and more wasted -specimens mav be traced on all the .adjacenTnrouiftains. The sculpture, too, of all the ridges and summits of this section of the , range is recognized at once as glacial, some of 1 the larger characters being still easily readable gfrom the .plains at a distance fifteen-or twenty .The Hot Creek Mountains, lying to the east of the Toquima and Monitor raages, reach the culminating point on a deeplv serrate ridge at a- height of 10,000 feet above the sea. This ridge Is found to be made up of a series of imposing towers and pinnacles which have been: eroded from the solid mass of the mountain by j a group of small residual glaciers, that lingered, in -their shadows long after the larger ice rivers had vanished. Oa it3 western declivities; are found a group of well-characterized moraines, canyons and rothes moutonees, all of: -^ich are unmistakably fresh and telling. The:- moraines iu paiiieular could hardly fail to attract the eye of any observer. Some of the- short laterals of the glaeier3 that drew their fountain snows from the j agged recesses of the Bummit are from one to two hundred feet in' height, and searce at all wasted as yet, not-' withstanding the countless storms that have fallen upon them, while cool rills flow between- them, watering charming gardens., of arctic- plants, saxifraxes, larkspurs, dwarf" birch, .- jibes and parnass'a, etc., beautiful memories ofr-. the ice age, -representing a once gieatly -- tended flora. " .-. . , In the course of explorations made to the/ eastward of here, between the 38th and 40th$ . parallels, I observed glacial phenomena equally- al facial period, and that if is. to this mighty host -a of- ice-streams, that all the more characteristic If of the present features of these mountain ranges 4« are due. But grand as is this. fresh arid demonstrative ( '■& ^'tfesjops of the mountains and filled the canyoas A mountains of the White Pine, Golden tiate-J- F.16% after the ice-sheet hadbeen broken up. J - ^*iSH^iS*!?^I!5!ftf5°?-t??J?„l1I??dJr. rl. r". GLACIAL TRACES. **The~ first glacial traces that I noticed .j are on the Wassuck, Augusta and Toi- iyibe ranges, consisting of ridges and canyons, : V ^rhose trends, contours and general sculpture are in great part specifically glacial, though , deeply" blurred by subsequent denudation, -j • • /These discoveries were made during the sum- -*>inerof 187&-7. And again, on the 17th of last' gust, while making the ascent of Mount Jef ferson, the don-inating mountain of the To- [- qnima range,! discovered an exceedingly in- I, terestiBg group of moraines, canyons with | V-shaped ero*s sections, wide neve' amphi- j theatres, mocntoneed rocks, glacier meadows, I and one glacier lake, all as fresh and telling j as if the glaciers to which they belonged had J descended on both sides scarcely vanished. *. from one stand-point X counted The best preserved and most regular of the ' 'moraines are two laterals about two hundred feet in height and- two miles long,- extending j from: the foot of a magnificent canyon valley j on the north tide ot the mountain andtrend- f-ing' first in a northerly direction, then curving atpund to the west, while a well character-: • ized » terminal moraine, formed by j the- slacier- towards the close of. its [ existence, unites them near their lower I-extremities at a height of 8,500 feet f»A»o'fcer pair of older lateral moraines, belong- 'ja<r t» a glacier of which.the one just men- .-F-3|i&«ff:'T»««'a tributary, extend in a. general '-' NM»»w«ster]y direction nearly to the level of I.Big.Smoky Valley; about 5,500feet above sea f> Four other canyons extending down the I eastern slopes ot this grand old mountain into f Monitor Valley are hardly less rich in glacial - t-records, while the effects of the mountain. c- shadows in controlling and directing the moye-s laments of theiesidual glaciers to which all these ^phenomena-belonged,-are everywhere delight-- I -fulryrapparent in the trends of the canyons and —;-aidees,- and in the.' massive sculpture.of the r-;f)nie"wombs. at.th£ii!.- heads. -This-U. a- v marked and imposing■- mountain,- attracting L: eye from agreatdistanefc^.-'—■ described only"as determined by differe»ces of elevation, relations to the snow-bearing winds, and the physical characteristics of the rock* formations. On the Jeff Davi3 group of toe* f Snake fJange, fhe dominating summit 0Tr! which is nearly 13,000 feet in elevation, and the highest ground in the basin, every marked, fertureisa glacier monument—peaks, valleys,- ridges, meadows and lakes. And becinse here.' the snow-fountains lay at a greater height,* while the roek, an exceedingly hard quartz!^,- offered superior resistance to- post-glacial agents, the ice-characters are on a larger scale, and are more sharply defined than any we have noticed^and it is probably here that the last, - lingering glacier of the basin was located. The summits and connecting ridges are mere blades> and points, ground sharp by the glaciers that —!i valleys', of these glacial channels with their moraines- sweeping grisdlj out to the plains to deep sheer-willed iieve-fountains at their heads, making a most vivid picture of the last days of the Ice Feriod. MOEE-ASCIENT GLACIiX ACTION. i.:' TlAve thusrfar directed* attention only upoii the meet recent and appreciable of the ptte- " nomenajAfft it must be borne in mind that less recentand less obvious traces of glacial action* abound' on*aR the ranges throughout the entrre * li&^»^erethe»anei,stria-, and grooves have : ;-:be?n ^bfiterjiSedi aaaVrSftat of the moraines ;~ hfls«*B«n'wash*a away, or so modified as to 4ST recognizable, and even the lakes , andmeadows,sochaiacteristicofglacialregion?, 7have. almost entirely vanished. For there. are other monuments, far more enduring than these, remaining tens of thousands of years after the more perishable records are lost. j Such are the-cafions, ridges and peaks them- j selves, the glacial peculiarities of whose trends and contours-cannot be hid from the eye of: the 1] skilled observerantil changes have been wrought I upon them far more destructive than those to "■Xj ' i .: :';. '/::■ delineated, in these old"record?, this-is-not all; for there is-not wanting evidence of a still grander glaciation estending over all the. valleys now forming, the sage-plains as well as.the ." DIRECTION OF THE ''lw.The. basins of the main valleys alternating J|! with the mountain ranges, and which eontained if lakes dnrrS"g at iea&t the closing portion of the j Ice period, were eroded wholly, or in part,. Tfrom a general elevated table-land, by immense r glaciers - that flowed north, and south to the I ocean. The mountains as well as the valleys ] present abundant evidence of this grand origin. The flanks of all the interior ranges are seen to have been heavily abrided and ground away ' by the ice acting in adirection parallel with their axes. This action is most strikingly shown I upon projecting portions where the pressure i has been greatest.-?These are.shorn, off in i; smooth planes and hossy outswelling curves,, j like the outstanding- poiiious of canon walls. i Moreover, the extremefies- of the. ranges taper 'I. out like those of dividing ridges which have '; 'been ground away by dividing and confluent 1 j glaciers. ._ Furthermore, the horizontalTsections of sep- aratcmountains, standing isolated in the great: valleys, are lenee-shaped like those of mere, rociis that rise in the channels of ordinary can- : yon glaciers,- aud which have been overflowed : or past-flowed.,, while in many of the smaller valleys roches montonees occur in great abund- FORMATION OF THE VALLT3T3. . Again, the mineralogical and physical-;char- acters of the two ranges bounding the sides of many-of the valleys indicate that the valleys' were formed-simply by the removal of tfce-mi- terial between the ranges. And again, the rim of the general basin, where it is elevated, as for examp-e on the south western portion, instead of being a ridge sculptured on the sides like a mountain range, is found Eo be composed of many short ranges, parallel to each other, and to the interior ranges, and so j modelled as to resemble a row of convex lenses set on edge and half buried beneath a general surface, without manifesting any dependence upon synclinal or anticlinal ases—a series of.foims and relations that could'have resulted only from the outflow of vast basin glaciers on their courses to the ocean. ire ux ma :r ^. , ™rr is a very ^ '.'■ ,.' .':: ts a smooth- v ,ft«jfgg'-) ihe-skfr a&jj ^^2^1 I cannot, however, present all the evidence here rbearing-upon these interesting questions, much less discuss it in all its relations, I will, UbeJfjfore, close "-this'tetter with a few of the more' important generalizations that have 'srowu up out of the facts that Ihave observed. First—At the beginning of the glacial period the region now kaown as the Great Basin was an elevated table-land, not furrowed as at present with mountains and valleys, but comparatively bald and featureless. Second—This tableland bounded oa the east and west by lofty ":~ ranees, but compi '" mMfJ ~:" which was discharged to the" ocean northward | ;and southward, and in ita-cflow brought mosij if not. . all> the-.-present interior! granges, and valleys into .-relief- by erosiop. j Third—As the glacial winter drew near its close 'the ice vanished from the lower portions- of the basin, which then became .l£k£s, into which separate glaciers descended^from the mountains. Then these mountain glaciers vanished, in turn, after sculp- •u-rirg-the ranges into their- present condition. Fourth—The. Tew immense, lakes extending over the lowlands, and in the midst of which. many of the* interior range's, stood" as island?, became shallow as the ice vanished from the mCantains, and separated into miny distinct- , lakesjWhosewatersnolongerreached theoceau. Most of these have disappeared by the filling, of ' their-. basins with detritus from the mountains, and.nbw form.sage plains and " alkali flat3." The transition from one to the other of these va- • rious conditions was gradualand orderly—first, . a nearly simple table land, then'a grand mer- -*ie=glace shedding itsr-siiveftcrawficg currents to ■ the sea, and &ecomin2: -gradually more '■wrinkled as unequal erosion;-Toughened its "bed,.and brought the higbestpeaks-above the purface, Then a land of. lakes, an almost con- ilinuous-"sheet of-.water stretching from the Sierra te the Wahsatcb, adorned with innu- 5 rcerable island mountains. , Then-a slow desci- ' iiation and decay to ijresent Conditions of sage jna'^andrf.n -_^ _ ": I 3pHH Mtjir.-
|
|---|