28o CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Professor Joseph Le Conte in 1872^ thought the valley 

 had been filled to its brim by a glacier and cut out by gla- 

 cial action. The remarkable verticality of the walls was 

 regarded as the result of the perpendicular cleavage of 

 the granite. The domes were regarded as due to a concen- 

 tric structure in the granite, combined with ice erosion. 

 Le Conte in a late paper ^ is now inclined to adopt the fault 

 theory of the origin of Yosemite, but he recognizes that 

 the exceptional verticality of the walls of the Yosemite is 

 especially due to the vertical "cleavage " (jointing) of the 

 granites of the region, and states that the walls are now 

 slowly receding by vertical scaling and thus retain their 

 perpendicularity. However, it appears to the writer that the 

 vertical walls of the Yosemite, together with its great depth, 

 form the strong points in favor of the fault theory, and that 

 if these phenomena can be otherwise accounted for, the 

 fault theory is no longer necessary. 



In the same paper Professor Le Conte considers that 

 transverse river canyons of the ordinary type have formed 

 b}^ erosion in the ordinary manner " along incipient fis- 

 sures," likewise transverse to the general trend of the 

 range. Professor Le Conte says: — 



In the elevation of a mountain range there is of necessity a stretch along 

 the axis proportioned to the amount of elevation, which must tend to produce 

 transverse fractures. It may produce real fissures or only what I call incipient 

 fissures, or a loosening and jointing along planes transverse to the axis. In 

 the Sierra it was probably mostly incipient fissures, sufficient to locate the 

 position and facilitate the excavation of the valleys. 



It might here be noted that joints formed as described 

 above would be tensile joints, while Becker and others 

 regard most of the joints referred to in this paper as com- 

 pression joints. 



John Muir, writing in 1873,^ supposed the valley, and 

 in fact the topography of the entire range from base to 

 summit, to have been the work of glacial ice. He noted 



1 On Some Aucieut Glaciers of the Sierras. Proc. Cat. Acad. Sci., Vol. IV, 1873, p. 261. 



- The Origin of Transverse Mountain Valleys and Some Glacial Phenomena in Those 

 of the Sierra Nevada. University Chronicle, Vol. I, No. 6, December, 189S, Berkeley, 

 California. 



^ Proc. Am. Assoc. Adv. Sci., Vol. XXIII, Part II, 1S75, pp. 49-64. 



