50 ' SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
The map (PL I) shows the areas in which the older Tertiary lavas 
are known to occur, and, while many areas have doubtless been missed 
in the present rapid survey, it is believed that the larger ones have 
been mapped. The ore deposits within these older rhyolites and 
andesites, so far as is at present known, are contained in the silicified 
and kaolinized portions. These are shown in fig. I. although it is cer- 
tain that many others exist which were not encountered in the course 
of the present work. In searching for such areas of altered rock, the 
peculiar rugged topography with its walls (commonly called " dikes" 
by prospector-) and pinnacle- (see p. 17) will be helpful in many in- 
stances. The compact, flinty texture of the silicified rocks, already de- 
scribed (see p. 17). is very characteristic. In the Kawich Range, 
Paleozoic quartzite has been mistaken by some for silicified rhyolite. 
The quartzite, however, can be distinguished by its more glassy ap- 
pearance a- well as by the presence in it of rounded sand grains or 
pebbles. In both the silicified rhyolite and the monzonitic and 
andesitic rocks vein.- occupy fault fissures, and prospect trenches 
and pits located on such fault- often bring good results. Within the 
silicified rhyolite in particular quartz veins should be carefully as- 
sayed, a- in this quartz the values in the rhyolite camps usually lie. 
Further, a yellow scaly coating similar to that from Goldfield, deter- 
mined by Dr. W. F. 1 Iillebrand " as a basic ferric-alkali sulphate, 
appears to be confined to joints in the immediate vicinity of ore 
deposits in rhyolite. 
DESCRIPTIVE GEOLOGY. 
In this section the different localities are described in the following 
order: The mountain ranges and valleys in the vicinity of Goldfieldj 
those to the north of Pahute Mesa; the mesa itself: the mountain 
ranges to the south of Pahute Mesa : the Amargosa Mountain system; 
Death Valley; and the Panamint Range. 
REGION ABOUT GOLDFIELD. 
In the northwest quarter of the area shown on the map, in the 
vicinity of Goldfield, are the Lone Mountain foothills, the Silver 
Peak Range, the Mount Jack-on. Goldfield, and Southern Klondike 
hill-, and Stonewall Mountain. The hills are characterized by a 
north-south extension, the trend verging toward northeast in several 
instances. Geologically they are marked by important develop- 
ments of the Cambrian rocks and the Siebert lake beds. 
"Bull. U. S. Geol. Survey No. 260, 1905, i>. 137. 
