178 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
quartzose rock, many portions of which are finely laminated. Asso- 
ciated with it are minor hands of brown, greenish, or purplish-gray 
shale, the laminae of which are in places paper thin. The quartzite 
apparently underlies the limestone south of Indian ranch and litho- 
logically resembles the Eureka quartzite (Ordovician). 
Lone Mountain limestone. — Small bodies of limestone, in part, at 
least, of Silurian age, protrude from the Tertiary lavas and Recent 
gravels at four points — 3 miles west of Bullfrog, three-fourths mile 
southwest of the Gold Bar mine, and H miles south and 2^ miles 
southeast of Indian ranch. The limestone is dark gray, dense, and 
of medium grain. Finer grained facies closely resemble litho- 
graphic limestone. Interbedded with the normal type are layers 
of intraformational conglomerate. Thin seams of calcite locall} 7 
cut the limestone in all directions. The limestone 1.1 miles south of 
Indian ranch clearly overlies a quartzite which is probably the 
Eureka quartzite; if so this is the Lone Mountain limestone. More- 
oxer, Mr. G. H. Garrey collected from the limestone inlier 4 miles 
northwest of Bullfrog a number of fossils which Mr. E. O. Ulrich 
Mates are of Silurian age. 
Siebert lake beds. — One mile north of Crystal Spring is a small 
outcrop of an arkose conglomerate. The well-rounded pebbles, 
which reach a diameter of 1 foot, consist of quartzite, jasperoid, . 
limestone, and medium-grained biotite granite. The first three are 
derived from Paleozoic rocks, while the granite resembles many 
post-Jurassic granites. The conglomerate is lithologically similar to 
the more conglomeratic of the Siebert lake beds of the Amargosa 
Range, and may well be contemporaneous with it. If such is the 
case the shore line of the lake must have been near Bullfrog. The 
relative ages of the rhyolite and the lake beds are unknown. 
Older alluvium. — On the northeastern face of the Bullfrog Hills 
and across Amargosa River to the east are hills and terraces dis- 
sected by the present streams. These hills and terraces are 
formed of detrital material similar to that now being deposited in 
stream beds and on the alluvial slopes. The deposits were made 
while Amargosa River was at a higher level and presumably are 
alluvial slope deposits of the older alluvium. Basalt bowlders (pre- 
sumably of Pliocene-Pleistocene age) are contained in the upper 
portion of the beds. 
KJXKOCS HOCKS. 
Post- Jurassic pegmatite and alaskite. — Pegmatite with alaskite 
occurs with the pre-Silurian schist west of Bullfrog and dikes of peg- 
matite cut the Eureka quartzite near Gold Center. (See p. 155.) West 
of Bullfrog the pegmatite grades into afaskite, but the former rock is 
