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Sierra Club Bulletin 



ceptional. Their origin is easily explained. They are simply split 

 ends of ridges which have been broken through by glaciers. 



For their perfect development the granite must be strong, and 

 have some of its vertical cleavage planes well developed, nearly 

 to the exclusion of all the others, especially of those belonging 

 to the diagonal and horizontal series. A powerful trunk glacier 

 must sweep past in front nearly in the direction of its cutting 

 planes, with small glaciers, tributary to the first, one on each 

 side of the ridge out of which the Capitan is to be made. This 



arrangement is illustrated in 

 Fig. 1 6, where A represents a 

 horizontal section of a Capitan 

 rock, exposing the edges of 

 the cleavage planes which de- 

 termined the character of its 

 face; B, the main glacier 

 sweeping down the valley in 

 front ; and C C, the tributaries 

 isolating it from the adjacent 

 softer granite. The three Cap- 

 itans figured stand thus related 

 to the glaciers of the region where they are found. I have met 

 with many others, all of which are thus situated, though in some 

 instances one or both of the side glaciers had been wanting, 

 leaving the resulting Capitan less perfect, considering the bold 

 advancing Yosemite Capitan as a typical form. 



When the principal surface features of the Sierra were being 

 blocked out, the main ice-sheet was continuous and moved in a 

 southerly direction, therefore the most perfect Capitans are in- 

 variably found on the north sides of valleys trending east and 

 west. The reason will be readily perceived by referring to Fig. 

 8 of No. I, "Mountain Sculpture," in Overland for May.* 



To illustrate still further how fully the split fronts of rocks 

 facing deep canons have the angles at which they stand meas- 

 ured by their cleavage planes, we give two examples (Figs. 17 

 and 18) of leaning fronts from the canon of the north fork of 

 the San Joaquin River. Sentinel and Cathedral rocks also are 

 found in other glacial canons, and in every instance their 



Fig. 16 



* Sierra Club Bulletin, Vol. IX, No. 4, page 233. 



