GEOGRAPHY, TOPOGRAPHY, AND GENERAL GEOLOGY. 
17 
thickness of the Carboniferous limestone may be due partly to erosion 
and partly to intrusion of andesite at different horizons. If it 
represents erosion, this is evidence of unconformity. Notwith- 
standing the conformity of structure, it is not unlikely that there 
may be a hiatus between the two systems, for the correlation of 
Late tuffaeeous rhyolite (400') 
Pyroxene andesite breccia and ag 
glomerate (100') 
Hornblende andesite breccia and 
agglomerate (150') 
Later trachyte (50') 
Pleistocene and Recent lake, stream. 
and outwash deposits 
5|] Pleistocene (?) conglomerate (100') 
Biotite-horn blende-pyroxene andesite 
(200') 
Biotitedacite(300'). 
Latest trachyte (150'-300'). 
ly tuffaeeous rhyolite (300'-400'). 
Early trachyte (50'-600'). 
Claron limestone, conglomerate, and 
sandstone (1,000' ?) 
Pinto sandstone, shale, conglomerate, 
and limestone lenses (1,500') 
Homestake limestone (50'-500'). 
Tertiary 
( La te 
Miocene). 
Tertiary 
(Eocene). 
Cretaceous. 
Bint ite andesite 
Carbonifer- 
ous ( .')■ 
Tertiary 
i Early 
Fig. 2.— Geologic column of the Iron Springs district. 
the two is fairly well based, and the Permian, Triassic, and sonic 
Jurassic sediments are lacking between them. 
The Eocene series outcrops in a zone still farther away from the 
laccoliths. It consists of limestone and conglomerate, characterized 
28463— Bull. 338—08 2 
