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POPULAR SCIENCE MONTHLY. 



greatly to its interest. The oldest lavas in the region seem to have 

 been rhyolites and andesites, then followed basic andesites and 

 basalts, and last of all the acid and glassy rhyolites of the Mono 

 craters. 



On the north side of the lake the tufas, built up by springs issu- 

 ing from beneath the water, form a most interesting study. Great 

 masses of calcareous material have been formed about the orifices 



Obsidian Flow South of Mono Lake. 



of these mineral springs, assuming odd and striking shapes. In the 

 desiccated lakes of the desert in southern Inyo County these calcare- 

 ous tufa deposits stand out in all their proportions. 



It is probable that the forces producing the recent volcanic 

 action are but slumbering, and that in the future, as in the past, 

 movements will continue to take place along this great fault line 

 bounding the Sierra Nevadas on the east. When the strain becomes 

 too great, earthquakes will be felt and possibly followed by eruptions 

 of lava. 



The most severe earthquake of which we have any record on the 

 Pacific coast of the United States was due to movement along this 

 fault. On March 26, 1872, nearly the whole of California and 

 Nevada was violently shaken. The loss of life was, however, con- 

 fined to Owen's Valley. At Lone Pine, near the foot of the valley, 



