Studies in the Formation of the Mountains in the Sierra Nevada, California.

I-.. NAM li.VI. Ill- i\u27 -i.\u27l . f., \ ,\ ! .\u27l I\u27- !!Kll\u27ll-illi.-tl l.i-i T ;. -. [t i-.-in - - :.-.- -ii:i - - t-a-i and sometimes west, in North ( there :-: \u27 \u27 \u27|\u27i,:\u27 \u27*\u27\u27 dip- i-. these dikes occur en a \a-!lv I :i i -j i-r Sf-.-sh in North Carol hi.-!, in (he tm- case formii ; in-idefablc exti !:\u27. and in/the flu r. limit -d cut uji !\u27 tra|j i in ( irtirti-eticul \ li.. ..iiitaili -!i:i. -1- to i..ili\u27ou ;i i..= -- h._ a mile ill -nt iiW-n ion-1! n-ilea! i-Jcnl: and in life la! ca-i the\ are Lii-niTa!! \ transverse to the strike, while in tin former the\ are luevalefMh eoiueidcnl v./fh it. rVa lev, feel or rods in breaihvfi. and rareh reacii- lii II,.- itii place, tin- formation isAerv barren of org \u27 n mains m its ;, iritit-rii outi-rops. imart.:iiif! vVry readily subject to (lenwfation, it- remnants e\ i re where lying/it trough-like depressions, tuviiig evidently suffered a much gneatcr aniontit of waste from erosion than the enclosing ami ui/ieilving formations. We have sVmc iiin! of the atnotmt of tl/fs waste in the fact that the whole ttrU-kness of the formation has been swept away from the brottd-baekeorler of the siat\u27-./ati\u27t in the oeeurrenee of :i third outcrop eastwarVf the Ik-ej* Kiver belt and several mile- from ii. of the same eastvrahih /\u27.bus adding many thousand feet to the former estimates wliich were based upon the last named outcrop. Again in North f lc it-ait***- o*w / N \ n uM.\u27Hi-ionv. Ill Carolina the heavies! conglomerates are found along tho castt-Hf iu.\u27injjn- of the format ion. the embedded bou\u27di r-:. of:, n moreifiau :i foot th dialui-l. i ei-i,.-ain-r of the triiibCii rock~, Ivijje between it and the At l.-mi ie.JTom uhicli. in laryre pata. its material wits derive.!. A iii I this liijjy\u27have been the last of Ilia! eastward ;7H(j northe.\u27tst- wai\u27i\u27l eon\u27iMi-nia! area I\u27eijuiii-d iy In.-Hail\u27- i\u27.\u27.:.\u27i it -iNaiis verv r:iiiin:iLf ihi-ory of the format ion of the palaeozoic rocks orsNew York\u27 and of the Appalachians and the northwest, which are w -tiibnted as to indicate an eastern origin. StfWES SS Titf; FjRi.Vi\u27Sox or M\u27CSTAIXS IS rut; St.saw X:rAiA. C.vi.iFoi.-NiA. Bv John Jlnu. vf Oakhri, (\u27a!. .UISIKU\u27I. \u27 TitEss studies in mountain building refer particularly to that portion of the Sierra which is embraced between Lat. ;(\u27.\u27, .\u27In and off3. It measures about two hundred miles in length by .ukkiI sixty in width, and attains an elevation along the axis, from $e*t thousand six hundred to nearly fifteen thousand feet above the sea, : Ti/:- jKifii T w:io-n--- -ampsnicil by a targe imak-r -A ii a-tr.i --. .-.-.i-! it i jrfesatt* t In- rca-L-Ui--i that th- \u27\u27.n-!?--:\u27 iUv A-MH-atn..:, -x-.-ia i a..t , ..i - : ll.t-ir !k.4 m--| - .iia-..-l A3 I\u27llis- Tili- ii.i- no ,--Mt:it.-l tin- alil.n-vait;...M rf -t ...-;; --!- of r\u27le \u27 muu:..:. ti-.a. ami in jonticr t-i tiae ;ui!:iar I line; -I te lhal i.- !:a- n-A rtad i-n-. f= iiwiux ia i.s ab-euce frtau OjUiai.!, vvlioa- tlu-y wtav ---ut.—Kme- 50 \u27.. N\u27A It\u27iiAl. IIJSTOKY. All the individual mountains distributed over this vast area. whether the precipitous ranks marshalled along the .smniuit. or the more beautiful and highly specialized domes and mounts ttot- ted ui i- the broad undulating flanks, or the immense bosses and angles projecting horizontally from the sides of valleys, have ail been brought into relief during the glacial epoch, by the direct mechanical action of the (Ce-sfeeet and the glaciers into which it afterwards separated. The chief phenomena presented are : !. Scratched and polished \u27 surfaces. \u272. Moraines. *\u27!. Moutonneed rock formsand sculpture in general, as seen ill valleys, rltlgCS, lake basins and separate mountains. The polished surfaces ocelli- in the summit and upper half of the middle region, in irregular patches, some of which are several acres in extent, and though they have been subjected to corroding influences for thousands of years, their mechanical excellence is such that they still reflect the sunbeams like glass. The most extensive areas arc found in the upper half of the middle region where the granite is most solid in structure and contains the greatest quantity of silex. They are brighter, and extend farther down on the axis of the range on the north xi\u27lta of valleys, because when wet by corroding rains and snows they are much sooner dried again, the north sides receiving sunshine, while the south reposes in shadows. The lowest patches occur at elevations of from three thousand five hundred to five thousand feet above sea level, and thirty to forty miles below- the summits, upon the driest and most enduring portions of vertical walls, where they are protected from the drip sod friction of water; also on hard swelling bosses onthc bottoms of valleys, where they are kept dry by bowlders. In the summit regions, small active glaciers still linger, which present moraines of even\u27 kind in process of formation. Those of the ancient glaciers are clad with forests and extend down through the middle region of the range. In the lower region, polished surfaces are entirely wanting. So also arc moraines, though the material which once composed them is found scattered, washed, crumbled and re-formed over and over again until its glacial origin would scarcely be suspected, unless we trace it back into the undisturbed moraines of the middle region. All of Ike magnificent forests of the Sierra are grousing upon mo- n. N\u27ATi\u27KAI. HISTORY. . .1 raine mil, which, as vet. has suffered little change since it was first eroded aud outspread for them by the ancient glaciers. The most impertshaWIe of the glacial phenomena under consideration, are the rn/a- --. rtilgen and rark iiuvtma.} the Irnt\u27i.i. shapes and geographical position of which, are specifically glacial. Yet even these are considerably obscured by post-sfiaeial weata- oring, and a growth of forests. The glacial phenomena therefore brighten and become more legible as we ascend to the fresh work of the living glaciers on the summits. Rock and snow avalanches have produced marked changes, but these are very much restricted in their range, aud have done little towards altering the glacial physiognomy even of the localities w here they prevail. On the slow and gentle withdrawal of the iee-mantlo, many a weak tower and impending brow were shattered by the first severe post-glacial earthquake, traces of which are still conspicuous in every sheer walled valley and around the bases of the summit Alps. To this inrlh\u27jiink\u27\u27 alone, which occurred at lens! three centuries ago, nine-tenths or more of the cliff taluses are m its stool once in hundreds or thousands of years. This brief survey of the various forces inees antly or occasionally in action, wasting the mountain surface, would at first lead us i- li. NATfKAI. Ills\u27! il;l . to siq-p.--.i- thai the total amount of dcgradat ion ;:.,-! be enormous. But on tin\u27 contrary so indestructible no- \u27ia- Sierra IJoeks, and so shod i-. \u27 -e period through which theyhave been exposed to these a-i mis, the general result is eoiitparativ el\ insignificant. \u271 :ili.sitet] striated ana-. e..n-i it tit ing -- considi rabie a fxr- I ton of the upper and mi. bib- region, have no! yet been degraded to the bue-hundreilth of an inch. Farther down, measuring tablets abound, bearing the signature of the ice sheet, while the amount of torrent erosion is certainly estimated by measuring tin- depth of their channels below the unchanged glaciated surfaces lining their banks. Still farther down, where the polished surfaces disappear, we have ither valuable data for otir estimates in the height of ;,oi holes drilled into the walls of gorges, and lu the form of the bottoms of the valleys containing these gorges.- Slimming up these results, we find tin- average quantity of postglacial denudation in the upper hall\u27 of tin- ranjje, cinbraeihu a /one twenty-live or thirty miles u i-j,-. ,,-,,,\u27\u27„-/,.\u27.;,/ ,,.,- ,,,,, ,.,-,-,,,/ ,, /,,,;!, „f thru iiuhis. That of the lower half has been much greater, probably several feet. Nevertheless i! is certain that the main features have not been radieaily altered. The jihi/sitiguomy of the range from base to summit is strictly glacial, liivcrs have traced shallow wrinkles, avalanches have made sears -upon it, and forests have bearded it. but the change is not greater than a feu years would make upon a human face exposed to winds and storms and the changing atmosphere. The multitudes of lofty mountains, distributed along the summit of the portion of the Sierra under consideration, are almost wholly unexplored. They have been entered hastily a! a few points adjacent to trails, and a few of the snore accessible have been ascended, such as Jits. Dana, l.yeii, Whitney, and Tyndail. while the graiid wilderness of mountains, from whose fastnesses the chief tributaries of the San Joaquin and King\u27s liivers take their rise, has been mapped from a distance without any attempt at detail. Their echoes are never stirred by the hunter\u27s rifle whether Indian or white man, for, excepting tin* wild sheep, there is no game to tempt him even to the lakes ami meadows that lie around their bases, while their glaciers, avalanche-swept aud crevassed, and thin labyrinths of yawning gulfs and crumbling precipices, offer dangers which only the most powerful motives could compel one to dare. 2 The.-e uld strah.jt-.J j et h ►!.-#, ate uitea ;uim-! a huinlreil I\u27eet ;th ;a- the river level*-. v.. s \: i i: u. iir-ror.v. Looking southward al umphrev, tie- peaks see iia- range from the ,-ummi! of Sit. r11 .!11. v. tin- peaks -i-i-n: \u27 in- sown broadcast over a wide area. Scores of them i-xc i thinH-n thousan i. many are fourteen t;i -1— sand lee! high, vel so eloselv a. \u27\u27 they -.,.! npa- \u27. i- i Ilia! few rise more than two thousand feci above their -\u27 -a proper liases. Even this degree of individuality is seldom attained, for they are -!il! further connected by the jag ---i walls that swoop across tin- interspaces from shoulder to shoulder in magninVenl curves. To give effectiveness to any one of them, those adjacent would Feuuirc lo be n-moved. However awe-inspiring and incomprehensible these vasf mountain assemblies seen) to be. i! ommou -in.:in and the facts .-!\u27 \u27heir individual history are problems easih solved In the pi!i.-!it student. Beginning with pinnacle-: which are the sriesllcsl of the summit ui umtaiiiots. No geologist iii claim thai each pinna--\u27. was formed by sjK-cial upheaval, nor that iia- little chasms which si-j.a- rate them vwi\u27i- madi\u27 by subsidence. :\u27 iia- rending of ihe rock, fin- many of them are scarcely a fool deep, and may be formed artificially wherever the structure is suitable, simply by the removal of a block or two that has been loosened by the development of cleavage planes. We therefore conclude that pinnacles were formed by the removal of the materials which once filled the intervening chasms. The \u27/ . -/ .) I\u27inttiielrg are from one to nearly a thousand feet in height, (heir forms and dimensions being determined not by euta- elysmic fissures but !y orderly joints and eb-avage plain\u27-.\u27, whVh give rise to leaning form- where the isivi nil pi: ..r are im-iisei, as oii tile erc-i of Mi. Kv the mouth of a tributary valley, that conducts to a erater-shajx-d tce-womh. From this womb the ancient tributary glacier emerged, which in thrusting itself into the main -alley trunk caused the depression we are stttdj ing. After maintaining the new trend, thus modified, for aitont a mile an-i a half, the huge valley swerves lightly to tin- right. Again searching for the cause, we discover another ice-grooved tn\u27lnitaiy valley entering on the Iff}, which likewise conducts back io an ice-womb, whoso glacier in uniting with the main valley trunk deflected it like the fust, as far as its force, modified by the direction, smoothness ami declivity of its channel, enabled it to do. Still lower down, the noble valley has been pushed round in a curve to the left by a series of small tributaries which, of course, entered on the light. 77c Dynamics if tin- Ancient Glaciers are sublimely simple: With each change in direction there is always a corresponding change in depth or width, or both. On Hearing the basin of the Tuolumne .Mer de Glace if. is seen to be swept entirely round ! i the \u27-vest by powerful ( nnv:;-.-, whkih descended few tbeftanfcs \u27,\u27 Uu. Dmm, G \u27 *. t.)rd ami othrm. Kverv where we see the --aiise delicate eOBSpi ;ia. iaf-$&F®„ and no other; throughout the whole periou ir foptAt\u27.om the valleys of the Sierra were lithe as serpents d wineeidaflt the touch of every tributary. As to their cmnparatici- size, ve find the. greater ike i basins the greater the imUeya which proceed from them. No such direct and simple relations exist between water currents an-i the valleys in which they flow. Thus the Tenaya basin is not i.ne-fumili the size of \u27he South Lyell. yet its valley is meh Itnrger, Indeed some valley- \u27 mi streams at all, and the topographical conditions of the ...t\ demonstrate the impossibility of their ever having had any. as we have already observed, have not eroded the li-..- hundred thousandth pari of the valley- in the iippi i and middle regions. Neither eon id , r- -,-a -. in! streams have i-M rei ed any appreciable influence upon ii.- ir formation, for their trend- ai.- .- \u27,. /-\u27ve, eroding backwards into the bases of the peaks and pinnacles, and thus increasing the effi cts of winter snow ava- laneh-s I hat sweep ! heir sides. Notwithstanding the ruinous, crumbling aspects of the summit peaks, they ha\e suffered Very little change since the close of the glacial period, for, if denudation had been rnore extensive, their separating cirques and gorges would he more encumbered with debris; we find only a mere sprinkling of detritus, and that very little material has been removed by jiost-glacial streams is proved by the fact that the small lake basins through which tln-v flow are riot yet filled up. We will briefly consider the formation nf a few special mountain peaks, as -.in illustration of the foregoing principles. The /.\u27/i .7 Itftftp lies due east from the Yosemite valley at a distance of about sixte.-n miles in a straight course. Large tributaries of the Merced, Tuolumne, Rush and San Joaquin Rivers. take their rise amid its ice and snow. Its geographical importance is augmented by it- having been the centre of dispersal for some of the most influential of the ancient glaciers. LijiV. the dominating mountain of the group, reaches an altitude of thirteen thousand two hundred feet, though it is only a few I\u27eel higher than adjacent peaks, and all that individually pertains to it is a small fragment less than a thousand feet high, the existence of which is owing to slight advantages of structure and IV. Minni m- ! !:!. \u27 position, which prevented i\u27 - b.-ing eroded a- fast as the common ma-- of the range. Glacial fountains are rounded in a horizontal direction at the hi ad :\u27 !\u27 the -alia- reason that thev are a\u27 the bottom, this being tin- form which otters greatest re-i-tJinec to glacial erosion. A s\u27-uu\u27eirciihir till/line i- thn.s formed, which the glaciers maintain in pushing their way back into the mountain again-! which they heath When !! ciimdUisinshac, !,.,,, pushed quite through th-- axis of the chain --r spurs,.tejftrtite mountains or peaks an ppuluced, the degree of whoso individuality depends upon the extent and \ aria! a m of the en -\u27 n. ay - i - that th snow ,!! t.-il in ii fountain ienlv and ,n b basins should pass through the iit-v,- condition so sn begin to erode at the ven fiead ; that this is the ease i shown Iy unmistakable I races of such erosion upon the bottoms and sides of wombs now empty. The change of climate which broke up tin- glacial p riod would naturally cause an earlier transformation of su-ov with eroding ice ami produce the present condition of filings as a necessary consequence. The effects of shadotrs in prolonging and intensifying the action of portions of glaciers are shown in moraines, lake luisins, and in the difference in form an-i sculpture between the north and south sides of valleys and mountains, facts which I cannot stop here to present. I; is only to their effects in the segregation of mountain masses thai I would direct particular attention. An exantiiurinn of tin- --\r.-lh-ut d. tailed map at Use Sierra, ftttjamtt to i¥wift}. made suid.-r the auspices of \u27 Geoloeiesl Survey, wfHsiftiw the diici fioii of extension of the glacial . rtphithcatrc*.-- (key are in a southerly direction, beneath lite protection of phswfcw--cast by peaks and ridges. Again, ii will be seen that because the Merced spur trends in a southerly direction, its western slopes are in shallow in the fo-rentVvtl, ifs eastern in the afternoon : consequently it has a series of ..glacial amphitheatres hi-Hi sides, while another ridge trends in an easterly direction and its southerly slopes ire scarcely at all in shadow, consequent ly all its glacial amphitheatres are on the northern slop- The same admirable obedit nee to shad .vs is con- picuons ia parts of the range; the few surviving glaciers are .-ecu follow! them. Glacier- are the onlv eri/ders trhich on- thttg ffocerneil. The Merced -pur, King about ten mih-s to the southeast of the Yosemite \al\-, and almost the same distance from the main axis, presents a ven instructive range of peak- eroded from a single :::::--. Tin- fragments are Ml. (lark, and lied. IShv-k. and Grey Mis. Here we have a range of peaks from eleven thousand live hundred to twelve thousand feet high, blocked out. by the heads of two series of glacier tributaries. The truly magnificent group of granite summits stretching forty miles from Mb Humphreys in a southerly direction is the loftiest of the chain, abounding in elevations of fourteen thousand feet, yet. considered individually, mere pyramids one or two thousand feet high, crowded together and s,-i npon a common base, like pine trees along a ridge. . Ms. Whitney lies io the south of this group, and although the very highest point of the range, geographically or scenieallv has no special significance; viewed from the north or south i! resembles a helmet or the Scotch Cap called Glengarry. Its stimuli! is somewhat flat, curving gently towards the Kern Uiver valley, but holding a bold, precipitous front towards Owen\u27s valhy of Home two thousand feet. These precipices gradually merge into accessible siop.es around from southwest t northwest. Mts. Dana, Humphreys, Kmerson and Ritter far exceed Whitney in grand impress!veness of mass ami outline. A few cold meadow- less hikes nestle around its base, but it possesses no glacier, ami the end of summer finds little snow on its north side, and none at all on the south. Towards the close of the.glacial epoch, the summit of what.is now called Mt. Whitney peered a f\u27ew hundred feet above a zone of sieve, which fed glaciers that descend towards Owen\u27s valb-y on the east, and Kern on the west. The former cut the eastern face of the mountain, the latter its,southern. western and northern flanks, conferring upon the mountain its special individuality. Instead, therefore, of its being a grand uplift, it is merely a portion of the common mountain mass which, from relative conditions of structure and position has suffered a little less degradation. The same is true of all the mountains under consideration. The difference between the peaks and the passes is not that one tire elevations and the other depressions ; both an- depressions differing only in degree, the abasement of the one having been clfcctcd at a slower rate are left behind as elevations. 8. NA\u27Il\u27iiAI. HI-TO\u27.iY. 59 l.ifh Bowed above, them. ---. i.-ii-oved summit peaks well marked. Ail weak nice disitp- Aii the mountains of the flanks have -.-u subji continued denudation of the ice slice\u27 Tin- transition from spiky, angular to these overswepl forms :-. exceedingly well tnarkei towers, pinnacles and crumbling angulai surfaces., at pear, leaving only knotty domes and ridge waves as illustrations on the grandest scale of the survival of the - strongest. Because the ice sheet was universal there remains upon ;dl tin- wide flanks of the Sierra not one weak mountain form. Near the upper limits of overflowed mountains there are n exceptions to this rule even in appearance. It is only where we descend to regions longer left bare by the ice. and therefore more weatln red hat we iin-1 instances of mountain rocks at rtm\u27i --//. .\u27a struct* .- ami strong inform. There is now a lock neat\u27 Yosemite which is ready to fall apart by the development of it- K. ;.* W. cleavage planes, yet it is certain that it once stood the strain of Yosemite Creek glacier. If the Sierra were built up of one spo-l.-- of rock homogeneous in structure, then we might have difficulty in finding data upon which to ground our estimates of the quantity of denudation accomplished by the ice sheet and scparaic glaciers in the development of the think mountains. Some portion of the main axis as well as outlying spurs are capped with slates, and, all the base is slatc-covercd. The circumstances connected with their occurrence in these localities furnished proof little short of demonstration that they once covered ail the range; and from their known thickness where they occur, we tn&y approximately estimate \u27he quantity remove! where\u27 they are u-:-!:..-- we mm find, but the rich profusion of