WAH-WEAH EAXGE. 569 



prominent ingredient. Like the trachytes, the rhyolites under the micro- 

 scope show the presence of apatite. 



It will be seen that there are represented here a wide range of acidic 

 types of volcanic rocks, embracing varieties from the extreme highly 

 siliceous rhyolites, with their characteristic structure, through quartz-bearing 

 trachytes, rough, light-gray, normal, sanidin-mica-trachytes, plagioclase- 

 hornblende-trachytes, to the augitic varieties, which show a marked miner- 

 alogical and physical resemblance to the rocks classed as augite-andesites. 



In Cortez Valley^ just east of the Wah-weah Eange, occurs an inter- 

 esting shallow alkaline lake, which, during the autumnal months, becomes 

 dry, depositing a considerable amount of sulphate of soda and common salt. 

 A sample collected in the month of July from the northern end of the val- 

 ley contained: 



Chloride of sodium : 78.31 



Sulphate of soda 21.11 



99.42 

 The aqueous solution was neutral. It contained, in addition to the 

 substances quantatively determined, minute traces of lime, potassa, lithia, 

 and boracic acid. - 



