,4 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
cessation of movement in it, since the phenocrysts are typically broken 
fragments. Apatite is an accessory mineral. 
Rhyolitic glasses that outcrop 3 miles south of. east of Diamondfield 
probably belong to the biotite-latite-rhyolite series. These gray per- 
litic glasses are poor in phenocrysts, although biotite and less com- 
monly feldspar and quartz arc locally present. Flow banding is evi- 
denced by slight alterations in the color and texture of various bands. 
The perlitic glass grades into spherulitic and dense pinkish-gray 
glassy rhyolites. The perlitic facies breaks readily into globular 
fragments along the perlitic parting. The clear glass in some thin 
sections contain- sparse phenocrysts of orthoclase, quartz, and biotite, 
while in other- the phenocrysts are more abundant and oligoclase is 
also present. 
The rhyolite in the southeast corner of the Goldfield hills has 
highly developed flow banding, and in consequence the rock has a 
platy structure which wrap- knotlike around the phenocrysts. 
Blackish glasses with numerous phenocrysts also occur. Microscopic 
examination -how- this glass to be in reality a latite with pheno- 
crysts of oligoclase, orthoclase, biotite, quartz, and hornblende. 
On the east -i< V of the ( roldfield-Lida road, -2\ miles south of Gold- 
field, is a poorly exposed area of rhyolite. The white lithoidal 
groundmass, much of it brown or red through iron ^tains. somewhat 
exceed- in bulk the abundant phenocrysts. The latter include glassy 
unstriated feldspar, somewhat less quartz, and a few black mica tab- 
lets. Fragment'- of a pumiceous rhyolite are present. Under the mi- 
croscope the groundmass appears a- a turbid, slightly devitrified 
glass, showing flow line- and spherulites. A few rather large oligo- 
clase phenocrysts are associated with those of orthoclase. quartz, and 
biotite. The phenocrysts are all somewhat embayed by magmatic 
corrosion and were broken into fragments during the flow of the nearly 
viscous lava. This rhyolite probably belongs to the series under con- 
sideration, although it may be one of the later rhyolites. One mile 
farther south a similar rhyolite outcrops, and this clearly belongs with 
the quart/ latite and rhyolite series, since it was a low boss when the 
mesa basalt was extruded and that formation flowed in a gentle arch 
over its surface. 
The quartz latite and associated rhyolite are older than the Siebert 
lake beds and younger than the ande-ite. 
Quartz basalt.— -The basalt to the east of the Lida road and 2 miles 
south of Goldfield is probably a portion of the quartz-basalt flow 
which Ransome found interbedded with the Siebert lake beds in the 
special area. 
Later rhyolite.— "Lying for the most part in a horizontal position 
upon the eroded Siebert lake beds is a rhyolite flow, which is sepaj 
rated from the overlying basalt by the Pliocene tuffs. This formation 
