PRE-TERTIARY AND TERTIARY IGNEOUS ROCKS. 
Similar rocks are the predominant formation from longitude 117° 
30', the border of the region, westward to the Sieri Nevada." 
From the uniform amount of mashing which 11: cks have su1 
fered it is evident that all are approximately of ti : age. They 
intrude the Paleozoic rocks where the two are in conta< md frag- 
ments of them are included in Tertiary lavas. The youngest of 
Paleozoic rocks is of Pennsylvanian age and the earliest lava is prob- 
ably Eocene; in consequence the granites are of post- Carboniferous 
and pre-Eocene age. It is shown in the section on geologic history 
( [). 39) that the close folding of the Paleozoic rocks occurred in post- 
Jurassic time and the granite intrusion is believed to have been a rela- 
tively late event in this period of deformation, an inference supported 
by the comparatively unmashed condition of the graiii.es. Their post- 
Jurassic age is thus probable, a conclusion in accord with that of 
Spurr for the granites of Silver Peak h and Goldfield c and that of 
Louderback d for those of the Humbolt region. This would make 
these granitoid rocks essentially contemporaneous with the gran- 
odiorite of the Sierra Nevada. 
Dikes and sheets of a ferromagnesian-poor quartz-monzonite por- 
phyry intrude Paleozoic sedimentary rocks and granite of the Silver 
Peak and Panamint ranges and of Slate Ridge. This rock near 
Lida is apparently cut by the diorite porphyry described in the next 
paragraph. It is presumably a second intrusion of the granitic 
lgma. 
Dikes of diorite porphyry and fewer intrusive masses of diorite 
becur in the Silver Peak, Panamint, Amargosa, and Cactus ranges, 
idle Gold Mountain and Slate ridges, and the Bullfrog, Mount Jack- 
son, and Lone Mountain hills. These rocks typically contain brown 
hornblende. They are younger than the Paleozoic rocks and the 
igneous rocks already described and nowhere were they observed 
utting Tertiary lavas. Pebbles of diorite porphyry occur in the 
iebert lake beds (Miocene) and the rock is probably of post- 
urassic and pre-Tertiary age. Its intrusion was the last event in 
he pre-Tertiary igneous activity. 
TERTIARY. 
The Tertiary rocks include a number of igneous rocks, lava flows 
nd fewer intrusive masses, and sediments laid down in lakes. The 
ccompanying table presents correlations of the Tertiary rocks of 
le various ranges 
« Spurr, J. E.. Bull. U. S. Geol. Survey No. 208, 1903, PI. I. 
& Spurr, J. E., Bimonthly Bull. Am. Inst. Min. Eng., 1905, X<>. •",. p. 955. 
c Spurr, J. E., Bull. U. S.. Geol. Survey No. 260, 1905, p. 133. 
d Louderback, G. D., Bull. Geol. Soc. America, vol. 15, 1904, p. .".::»;, 
