SUCCESSION OF THE LAVAS 259 



entire, of plagioclase, sanidine, quartz, and biotite, in a groundmass that 

 appears to be devitrified glass. A similar dacite, but massive instead of 

 fragmental, is found farther west, at the north base of the range, and this 

 is probably of the same age as the tuff in the Miocene beds. 



ANDESITE AND RHYOLITE 



Higher up in the lake beds, apparently near the middle of the forma- 

 tion, are rhyolite and andesite tuffs, the andesite being of the normal 

 type. In the ravines at the east base of the Silver Peak range, just south 

 of the Emigrant road, there is a layer of andesitic breccia about 20 feet 

 thick, interstratified with lacustral marls, and 200 feet higher up, or to 

 the east, is a thicker layer of rhyolitic tuff. Both of these layers contain 

 silicified wood. What are perhaps the same layers are to be seen in the 

 lake beds to the east of the Silver Peak road, in the south end of Big 

 Smoky valley. There are also pebbles of andesite and rhyolite in the 

 older conglomerates of the Esmeralda formation, about 3 miles west of 

 Ehyolite ridge. A very striking evidence of the succession of lavas is 

 seen in the ridge west of Ice House canyon when viewed from Fish Lake 

 valley. At the west base are gray andesite breccias 800 feet in thickness ; 

 next, white rhyolite tuffs of about the same thickness capped with a flow 

 of dark basalt ; but if we go up Ice House canyon we will observe that the 

 succession is not so simple, for overlying the rhyolite tuffs above referred 

 to is another extensive andesite-tuff area, succeeded by other rhyolite 

 tuffs and pumice, which to the east of the canyon are associated with and 

 appear to be interbedded with sandstones of the Esmeralda formation. 



The highest, and therefore most recent, tuffs and pumice beds are 

 finally capped by the coarse basalt of the Piper Peak flow, which is an 

 hypersthene-basalt, while that of the ridge west of the Ice House canyon 

 is a normal, dark, fine grained, olivine basalt. 



The succession of lavas in Ice House canyon would then apparently be : 



1. Older basalt associated with the red basal conglomerate of the 



Esmeralda formation. 



2. Andesite-breccia. 



3. Rhyolite-tuff. 



4. Andesite-breccia. 



5. Rhyolite-tuff and pumice. 



6. Hyperstbene-basalt of Piper peak. 



7. Dark fine grained olivine-basalt, which may or may not be later 



than the Piper Peak flow. 



In the northern foothills of the Palmetto mountains and the adjacent 

 foothills of the Silver Peak range there are extensive areas of hornblende 

 and pyroxene-andesite overlying rhyolitic tuffs and pumice, and this is 



