164 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
head of a gulch. The sheet is over 200 feet thick and is at least one- 
fourth mile long. This schistose rock is composed largely of horn- 
blende, with some quartz and feldspar. Red garnets which reach 
a maximum diameter of one-half inch are abundant in some portions 
of it and are also present in the adjacent sericite schist. The horn- 
blende schist is composed of the following minerals, named in the or- 
der of their abundance : Hornblende, quartz, biotite, plagioclase 
(oligoclase in part), orthoclase, garnet, magnetite, and apatite. The 
rock has the form of a sheet injected in the Cambrian rocks. This 
schist and the gneiss above described, each of which is probably a 
mashed basic igneous rock, are the oldest igneous rocks known in the 
area surveyed. The hornblende rocks are older than the post-Juras- 
sic granite, which is everywhere massive, and since they have suffered 
approximately the same metamorphism as the rocks which they in- 
ject they are probably of Paleozoic age. 
The sedimentary rocks of this series were laid down in a shallow- 
sea in which the conditions of deposition were constantly and rapidly 
changing. Fragmental material was carried into the sea even during 
the deposition of limestone, since clastic quartz grains are common 
in it. 
The series is identical with that of Tucki Mountain, in the Pana- 
mint Range. Its age was not definitely determined, since unfor- 
tunately the contact with the Ordovician and Silurian rocks lies 
between two traverses made across the range. Lithologically it 
more closely resembles the Prospect Mountain quartzite (Cambrian) 
of the Specter Range than any other formation. The two are both 
quartzites, with shale and conglomeratic facies containing similar 
pebbles. Limestone was. however, not noted in the quartzite of the 
Specter Range. While tentatively considered Cambrian, these sedi- 
mentary rocks may in reality be of pre-Cambrian age. The severe 
metamorphism of the series indicates that the rocks have undergone 
folding not suffered by the Ordovician rocks farther north, and that 
they are hence of pre-Ordovician age. 
Pogonip limestone. — The Pogonip limestone extends from Keane 
Springs northwestward to Grapevine Canyon. It also covers a large 
area north of Grapevine Springs and smaller areas in the vicinity 
of and north of the Staininger ranch, east of Cave Rock Spring, and 
4 miles east of boundary post No. 94. In the large area north of 
Keane Spring from 2,000 to 3,000 feet of limestone is exposed. It 
is a fine- to medium-grained dense rock, most of it dark gray or black 
in color, though some beds are light gray. The lamina? are as a rule 
from one-sixteenth to one-fourth inch thick, while the bedding planes 
are from 4 inches to 40 feet apart, heavy bedding being rather 
characteristic. Calcite veinlets anastomose throughout the lime- 
stone mass, and in Titus Canyon areas of coarse white calcite blotch 
