498 PROCEEDINGS OF THE ALBANY MEETING 



GEOLOGY OF THE GREAT BASIN IN CALIFORNIA AND NEVADA * 



BY H. W. TURNER 



\^ Abstract] 



The ridges of the western edge of the Great Basin in Nevada and eastern Cali- 

 fornia are usually very complex in structure and composition. They comprise 

 sediments of Paleozoic and Jura-Trias age, much disturbed at some points by in- 

 trusions of granolites. In Tertiary time there were extensive lakes, and contem- 

 poraneous with these lakes, and also later, are lavas and tuffs in large amounts, 

 chiefly rhyolites, andesites, and nasalts. 



Structurally, the region is characterized by ranges upheaved along normal faults, 

 but in places previously folded. A portion of the Silver Peak range is composed 

 of a series of granites, gneisse.s, and schists which are pre-Cambrian in age and 

 presumably Archean. The sedimentary rocks range from the oldest Cambrian to 

 Recent, but no rocks of Cretaceous age are known to be present. The Paleozoic 

 and older Mesozoic terranes are intruded by a great variety of granolites. There 

 is some serpentine that appears to have formed from diopside, that mineral pos- 

 sibly being derived from the metamorphism of magnesian limestone. 



The formation of the ranges, or at least their latest uplifts, dates from the late 

 Tertiary and post- Tertiary time. 



They were elevated along normal faults, the valleys being in part subsided areas, 

 often of the nature of rock basins, whose rims are composed of rocks older than 

 the desert detritus. 



There are some gneisses pretty certainly of pre-Cambrian age. These gneisses 

 underlie Lower Cambrian sediments rich in fossil remains at some points. There 

 is an extensive chert series containing abundant graptolites supposed to be of 

 Lower Silurian age. There are Lower Trias beds in the Inyo range and Jurassic 

 limestone in the Pilot mountains. 



The lavas consist of a Paleozoic series comprising meta-rhyolites, keratophyres, 

 and meta-dacites and a Tertiary series of rhyolites, latites, dacites, andesites, and 

 basalts, the succession taken in a large way being about in the order named. 

 There are, however, rhyolites and andesites of different ages, and one type of 

 dacite is among the oldest of the Tertiar}' lavas. 



The supposed Archean rocks contain gold-silver quartz veins of great value. 



A series of Tertiary lake beds contain beds of coal and abundant plant, mollus- 

 can, and fish remains and the playas of the valleys rich deposits of chloride of 

 sodium and borax. 



GEOLOGY OF THE THREE SISTERS, OREGON 

 BY H. W. FAIRBANKS 



[Abstract] 



The Three Sisters form a group of volcanic peaks on the summit of the Cascade 

 range in central Oregon. They rise to a height of about 10,000 feet, and are quite 

 similar in many respects to the other great volcanic peaks which mark the crest of 

 the Cascade range through Oregon and Washington. • 



* The paper was illustrated with lantern slides. 



