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Sierra Club Bulletin 



weathering, and affords the deepest, as well as widest naked 

 sections, the former in Yosemitic canons, the latter in flat basins 

 like those of Yosemite Creek, Lake Tenaya, and upper Tuol- 

 umne Valley, wherein broad areas of glacier-polished granite 

 are spread out, as clean and unblurred as new maps. 



I should have stated that the three series of cutting planes 

 mentioned above are not the only ones existing in these rocks, 

 but we will consider them first, because they are most marked 

 in their modes of development, and have come most prominently 

 into play in the formation of those unrivaled cafions and rocks 

 which have made the Sierra famous. In studying their direc- 

 tion and range, we find that they extend along the west flank 

 from latitude 36° to 40° at least, and from the summit to the 

 soil-covered foot-hills, and in all probability further observa- 

 tion would show that they are co-extensive with the length and 

 breadth of the chain. We measured the direction of the strike 

 of hundreds, belonging to the two vertical series, many of which 

 run unbrokenly for miles in a tolerably uniform course, the bet- 

 ter developed ones nearly at right angles to the axis of the 

 range, the other parallel with it. Canon sections show that they 

 cleave the granite nearly vertically to a depth of 5,000 feet with- 

 out betraying any tendency to give out. The horizontal series ap- 

 pear also to be universal. In some places these divisional planes 

 are extended within a few inches of each other, while in others 

 only one conspicuous seam is visible in a breadth of bare rock 

 half a mile in extent. Again, many large domes occur that ex- 



FlG. I 



