ACADEMY OP SCIENCES. 261 



4. Carxon Cation Glacier. — Hope Valley, (with its southward continu- 

 ation as Faith and Charity valleys) and Lake Tahoe Valley lie counter-sunk on 

 the very tops of the Sierras, in the direction of the range, and therefore divide it 

 into two crests:, one east and one west of these valleys. The author finds 

 abundant evidence of a great glacier, which, taking its rise in a group of snowy 

 peaks to the southward, flowed northward, filling Charity, Faith and Hope val- 

 leys as a great iner de glace, and then turning at right angles, escaped through 

 Carson Canon, eastward to the plains of Carson. From Hope Valley nier de 

 glace an overflow branch, also, probably ran in the opposite direction into 

 Lake Valley. 



5. Lake Valley Glacier. — The same group of snowy peaks, already mentioned, 

 gave origin also to another and still grander glacier, which flowed nearly par- 

 allel to the last, but extended much farther northward. It filled Lake Valley, 

 the whole of the basin of Lake Tahoe, and escaped through Truckee Canon, 

 eastward to the plains. Evidences were observed of a former higher and more 

 extended condition of Lake Tahoe. 



G. American River Canon Glacier. — Johnson's Pass (the pass over the 

 western crest) gives origin to two glaciers ; a smaller one running eastward and 

 forming one of the more important tributaries of Lake Valley Glacier, and a 

 much larger one rwnmn^ westward through the grand canon of the South Fork 

 of the American River, for twenty-five or more miles. The canon at Sugar 

 Loaf, near the junction of granite with the slate, becomes very narrow, deep 

 and precipitous. In this narrow gorge the glaciated forms are very fine. 



SOME GENERAL CONSIDERATIONS. 



A. Ice-sheet in California. — In the fullness of glacial times, the polar ice- 

 caps, the author thinks, extended along the Sierras probably even to Southern 

 California. The direction of its flow was probably east and west, determined 

 by the slope of this great chain rather than by northern elevation. This gen- 

 eral Sierra ice-sheet, from its lower margins, stretched out icy fingers, or sepa- 

 rate glaciers, east and west, still lower down the valleys. The evidence of this 

 ice-sheet is seen in domes and dome-like forms, which the author regards as 

 montonnee forms on a huge scale. 



The granite about Yosemite is affected with two kinds of structure, viz. : A 

 concentric structure on a grand scale, and a perpendicular cleavage. The former 

 is well shown in the Royal Arches and in the domes ; the latter in the perpen- 

 dicular clifls and spires about Yosemite. The domes and dome-like forms so 

 abundant about Yosemite, seem to be the combined result of ice-erosion and 

 concentric structure. 



B. Origin of Yosemite. — The perpendicular cliffs of Yosemite are sup- 

 posed to indicate either fracture or sudden engulfment by earthquake shock. 

 If Yosemite were unique, this theory might be credible ; but Yosemite is not 

 unique. The author shows, that many of the great glacial canons become deep, 

 narrow gorges with precipitous walls, near the junction of the granite with the 

 slate. This is the position of Yosemite, of Iletch-hetchy, and of the gorge of 



