1872.] 39 (Kneeland. 
Prof. Whitney, who has given this region more study than any other 
geologist, this structure is not the result of the original stratification 
of the rock, and there are no evidences of anticlinal or synclinal 
axes; the curves, arranged strictly with reference to the surface of 
the masses of rock, show, in his opinion, that they were produced by 
the contraction of the material while cooling or solidifying, giving 
the impression that one sees the original shape of the surface. That 
the peculiar appearance of these dome-like structures, very general 
in this portion of the Sierra, is not the result of ice or water action, 
is shown by the overlapping of these concentric granite plates, over- 
hanging the valley, and causing the enormous cavities or ‘‘ Arches,’ 
left by the fall of the masses from the action of the frost and the ele- 
ments, at the present time hich above the reach of ice or water. 
According to Mr. Muir, as taken from his published and unpub- 
lished letters to newspapers and friends, there were in the Merced 
basin,— bounded by the ridge extending from Mt. Lyell northwest- 
erly to the Cathedral Peak and to Mt. Hoffman; by a shorter paral- 
lel ridge eight or ten miles to the westward, running also northwesterly 
to Mt. Clark of the Obelisk group; and a connecting ridge running a 
little east of north to Mt. Lyell, this last being the divide between the 
tributaries of the Merced river on the north and the San Joaquin on 
the south, an area ten miles square on each side of the middle or 
Nevada cafion of the Yosemite valley —there were three great cen- 
tral glaciers, named respectively from the south northward: 1. The 
Nevada, coming down the caiion of that name, through the little or 
upper Yosemite valley, in which now flows the main stream of the 
Merced with the Nevada and the Vernal falls, flowing in a gener- 
ally west direction from the Lyell group, and about twelve miles long. 
2. The Tenaya, in the cafion of that name, coming down by Cloud’s 
Rest and, leaving as its most beautiful traces the Tenaya and Mirror 
Lakes — flowing in a southwesterly direction from the Cathedral 
Peak and the neighboring summits; of about the same size at the Ne- 
vada glacier. 3. The Hoffman glacier, from the easterly slope of 
the mountain cf that name, coming into the valley by Indian cafion, 
the North Dome, and the Glacier cafion. The marks left by these 
glaciers, miles in length and width, and thousands of feet in thick- 
ness, are now the polished surfaces, the smoothed domes, the exten- 
sive moraines, the beautiful lakes, and the green meadows — the 
strie and grooves are mostly obliterated by the frosts and the rains 
