4i6 



Sierra Club Bulletin 



descent. Where it strikes a projecting boss it gives forth an 

 intense gasping sound, which, coming through the darkness of 

 a storm-night, is indescribably impressive; and v^hen at length 

 it plunges into the valley, the ground trembles as if shaken by 

 an earthquake. 



On the I2th of March, 1873, I witnessed a magnificent ava- 

 lanche in Yosemite Valley from the base of the second of the 

 Three Brothers. A massive stream of blocks bounded from 

 ledge to ledge and plunged into the talus below with a display 

 of energy inexpressibly wild and exciting. Fine gray foam- 

 dust boiled and swirled along its path, and gradually rose 

 above the top of the cliff, appearing as a dusky cloud on the 

 calm sky. Unmistakable traces of similar avalanches are vis- 

 ible here, probably caused by the decomposition of the feld- 

 spathic veins with which the granite is interlaced. 



Earthquakes, though not of frequent occurrence in the Si- 

 erra, are powerful causes of avalanches. Many a lofty tower 

 and impending brow stood firm through the storms of the first 

 post-glacial seasons. Torrents swept their bases, and winds 

 and snows slipped glancingly down their polished sides, with- 

 out much greater erosive effect than the passage of cloud- 

 shadows. But at length the new-born mountains were shaken 

 by an earthquake-storm, and thousands of avalanches from 

 canon walls and mountain sides fell in one simultaneous crash. 

 The records of this first post-glacial earthquake present them- 

 selves in every canon and around the bases of every mountain 

 summit that I have visited; and it is a fact of great geological 

 interest that to it alone more than nine-tenths of all the cliff 

 taluses which form so striking a characteristic of cafion scen- 

 ery are due. The largest of these earthquake taluses are from 

 500 to 1000 feet in height, and are timbered with spruce, pine, 

 and live-oak over their entire surfaces, showing that they have 

 not been disturbed since their formation, either by denudation 

 or accessions of fresh material. 



The earthquake which destroyed the village of Lone Pine, 

 in March, 1872, shook the Sierra with considerable violence, 

 giving rise to many new taluses, the formation of one of which 

 I was so fortunate as to witness. 



The denuding action of avalanches is not unlike that of 



