spurr.] ORE DEPOSITS OF TONOPAH AND VICINITY, NEVADA. 85 
able depth. Part of the formation is made up entirely of myriads of 
the microscopic siliceous shells of infusoria. Since the lake epoch, 
however, erosion has been considerable, leaving the tuff forming some 
of the low mountains in the vicinity. 
There was apparently a later flow of rhyolite, in general compo- 
sition like the earlier flow, but distinct in point of age and now 
consequently fresher in appearance. Some mineralization followed 
this flow, producing veins and coatings of chalcedony, iron car- 
bonate, iron oxide, etc., along the contact and in crevices in the 
adjoining rocks. These veins also carry small amounts of gold and 
silver, but have no connection with the earlier, more important min- 
eralization. 
Latest of all was the eruption of lava which forms most of the 
mountains around Tonopah. The nature of this lava is dacitic. a 
The writer spent two months in the autumn of 1902 making a pre- 
liminary investigation of the Tonapah mining district. Mr. W. J. 
Peters, of the topographic branch of the Survey, has just finished 
making a careful map of that portion of the district which is of great- 
est economic importance. This map is on a scale of 800 feet to the 
inch. The writer will continue and finish his investigation in the 
spring of 1903; will map the different geologic formations, and will 
prepare a report showing the relation of the ore deposits to the 
different rocks. 
There are several perplexing problems which are to be worked out 
in the district. One of the most important is the location, as nearly 
as possible, of the underground course of the upper contact of the 
earlier andesite or lode porphyry, so that mining men may know 
approximately where to sink their shafts with the chances of reaching 
the porphyry soonest. Another difficult problem will be to ascertain, 
if possible, the probable course and extension of the vein systems of 
the district. A third problem, perhaps the most important of all, is 
the study of the distribution of the rich ores within these veins. 
These questions will be dealt with in the forthcoming report. 
ORE DEPOSITS IN VICINITY OF TONOPAH. 
The writer made a number of brief examinations of certain ore 
deposits in the vicinity of Tonopah. 
Silver Peak district. — A slight examination was made of the prin- 
cipal mine in the Silver Peak district. This mine is on quartz veins 
of great thickness and surface extent, which hold relatively small 
quantities of gold. The veins have been worked near the surface for 
many j^ears past, although lately activity has not been very great. It 
is claimed that three-quarters of a million dollars' worth of ore has 
already been extracted. There are two parallel veins lying close to 
« Dacite is quartz -hearing andesite. 
