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Show APPENDIX NN. 1293 olwerver states that all the other sierra lakes he has seen certainly owe their origin to glacial agency. Lake Tahoe has been partly shaped by the same operation, and traces of glacial deltas are found along tbe western shore. Le Conte thinks careful examination would discover the pathways of glaciers run-niug into tbe lake from the eastern summit, but be failed to detect any evidences of them. Iu my own examination of this range I found no traces of glaciers, particularly no glacial scratches. There are some bowlders scattered over the eastern side of the r< tnge that may have been transported by glacitrs. v Tbe predominating rock in tbe western summit is granite. But igneous rocks such os basalt, diorite, and phonolite have broken through the granite iu several places. This range may be fitly divided iuto the Pyramid Peak ridge, the Tallac Peak ridge, tbe Twin Peak ridge, and the ridge north of Trnckee Cation. Beginning on the south, the Pyramid Peak ridge consists chiefly of granite. This is the westernmost ridge of the western summit, aod its southern boundary is tbe American Fork CaFion, a narrow, windy valley with precipitous sides composed of gray granite. The peak itself is a mass of coarse- grained, yellowish granite, iu the form of a pyramid, rising about 300 feet above the ridge- line. The altitude of Pyramid Peak id 10 003 feet. The north side of this peak is much steeper than the other sides. Angular fragment* of granite cover tbe slopes of Pyramid Peak for a distance of a quarter to * a half mile from the top. There is a small grass patch on the northeast side of the mountain. The eastern declivity of Pyramid Peak passes gradually into tbe (> Devil's Basin/' a vast amphitheater of granite, probably formed by glacial agency, and containing a series of bkelrts. A 6errated ridge forms the eastern bouudary of this basin. The rock is grayish grauite, with large, dark specks of the same rock disseminated through it at the point where the Placerville road crosses the western summit. At first fright these spots presented the appearance of hornblende, but on close examination it was fonud that they were only a darker variety of the granite, although the forms were six- sided. This peculiarity of structure was observed frequently in the southern portion of the western summit. About a mile north of the Placerville road is Echo Lake, ( 7,478 feet high,) which forms the outlet of a lake- basin extending several miles to the westward. Numerous islands occur iu the lakes of this basin, and son e of them have a little soil and a few trees. The rock bordering Echo Lake is g ay syenitic granite, which is much t aversed by joints. Ou the northeast side of this lake a wall of granite rises abruptly to a he'ght of several hundred feet, and forms the southern end of a mass of the same rock extending north to Gilmore's Cafion. Although not strictly belonging to the western summit, a brief description of Lake Valley may be given here. Tbe greater part of this valley is Quaternary. There is no rock in situ for 4 or 5 miles from Lake Tahoe. A morass covered with coniferous trees extends back from the lake about half a mile, and east and west for a mile and a half. Lake- weed and eel- grass abound in this martb, where the water varies from 6 inches to 3 feet in depth. Mallard ducks and grebes are common. The sandy beach en the northern side of Lake Valley is lined with alder bushes. About five miles from Rowland's, near Barton's ranch, two buttes of gray granite occur. Black mica, limpid quartz, and grayish- white feldspar are the constituents of the rock. Th « * buttes are several huudred feet in height, and may be considered as outliers of either the wt stern or eastern summits. Tbe country between these buttes is strewed with large granitic bowlders. At the head of Lake Valley, near Hawley's ranch, dark grayish graphite occurs with quartz. A wagon- road runs from Rowland's along the eastern side of Fallen Leaf Lake to Soda Springs, two miles from Gilmore's ranch, on the lake. According to the aneroid, the springs are 325 feet above it. Tbe temperature of the water is 46} Q F. The spring- water contains carbonic acid, sesquioxide of iron, and snlphur-eted hydrogen. It is bottled and sold at Rowland's and other hotels ou Lake Tahoe. The Tallac Peak ridge runs from Gilmore's Canon to Blackwood Cafion. Between this ridge and that of Pyramid Peak are two minor ridges without any name, composed of inany dome- shaped pesksand rocky tors alternating with V- shaped ravineB. A vast amphitheater bounds Tallac Peak on tbexsouth. The rock is gray granite as far as the springs, where it passes iuto basalt, having a slaty structure. The creek which flows into Fallen Leaf Lake has cut a small channel tn the bottom of this basin, in which are a few cascades. There are several lateral cafions on tbe sonth side of Gilmore's Canon, which rise in rocky terraces one behind another. The western and southern portions of Gilmore's Canon afford fine examples of Roches Moutonnets. The rock is grauite on these sides of the cafion and basalt on the northern. A small number of conifers are scattered over the cafion. Mount Tallac is a mass of bluish basalt upheaved through granite. The rozk shows nearly every variety of structure known to the members of the basaltic groups. There tire both grannlar and compact species. Some specimens are porphy-ritic with compact matrix. Incrustations of olivine occnr in places. Nearly all the northeast side of Tallac Peak is composed of compact basalt. The wall of rock forming this side rises perpendicularly 700 feet or more from the plateau to the east of it. Three detached masses of rock that have undergone much disintegration project from the face of the main peak. The jointed structure of the basalt has been favorable to |
