Calcite and a greenish talcose mineral occur as alteration prod- 

 ucts. In their section the feldspar is seen to be greatly altered. 

 The biotite is partly decomposed. Dr. Wadsworth, however, 

 regards these two varieties as parts of the same formation. This 

 specimen was taken from the very crest and like all the rest of 

 the top of the mountain is so decomposed as to yield readily to 

 the hammer. 



The lower two-thirds of the walls of the great basin, including 

 approximately the upper limit of the gray variety, is "arranged 

 (on the western side) in concentric sheets that dip west at an 

 angle varying from 45 to 6o." On the southern wall the 

 concentric layers dip north often at angles greater than 60. The 

 red granite caps these concentric sheets. Upon weathering it 

 splits into blocks more or less regular in form which strongly 

 resemble "courses of cyclopean, but crumbling masonry." So 

 friable is this rock that it readily crumbles under the slightest 

 weight, giving rise to a residual granitic soil, the only original 

 soil of the mountain. 



"The forms which the several parts of the mountain now 

 present, and the condition of their surfaces, are largely due to 

 the original structure and mode of weathering that characterize 

 the rocks. As the highly inclined concentric sheets in the basin 

 walls break away, and fall upon the talus below, other faces of 

 equal inclination are exposed; while the red granite of the higher 

 parts, deprived of support, in turn gives way, and thus the steep- 

 ness of the walls is maintained." Similar explanation applies 

 to precipitous faces upon other parts of the mountain. 



That part of the crest between East peak and Chimney owes 

 its form and preservation to the circumstance that the modified 

 red granite which makes it up divides in weathering into plates 

 which, when undisturbed stand vertically on edge * * * * 

 a mere blade of rock from one to two feet wide, having upon 

 one side the yawning gulf of the basin (South basin) and on the 

 other cliffs too steep for climbing." These plates "vary in. thick- 

 ness from an inch, or less, to upwards of a foot." When they 

 loosen, under frost action, and crash down the cliffs on either 

 side, the plates remaining constitute the ever narrowing and low- 

 ering crest. Between East and West peaks the rock plates stand 

 across the ridge at various angles. Loosened by frost -the plates 



10 



