Geology. 475 
formability beneath these mountains. But in the region of the 
anon, the Carboniferous, Triassic, Jurassic, Cretaceous and Ter- 
tiary beds are all conformable. e epochs of mountain-making 
over the Pacific slope south of the latitudes of the Wahsatch Range, 
and also of that of the north, were different from those within 
these latitudes. 
(2.) Mr. James T, Gardner, in a letter of May 8th, informs me 
western-border, central and eastern-border chains of the Great 
sin. The precise determination of the epoch of origin of the 
Humboldt chain is therefore of much importance. 
under the influence of geologists. Variations of the surface forms 
sev istin 
photographer three 
ie as 
4 draughtsman ; a quartermaster | : 
The field of operations authorized by Congress for the coming 
season is the Territory of Colorado, and that gags of Utah lying 
east of the Green River. It is peers on the pore BY ech ga 
of the 40th Parallel S d the primary triangulation will 
ye pap ay es ng across a the Sierra Nevada 
@ part of the same system ed acr 
by that survey. The work will be based upon a t 
Am. Jour. Sc.—Turrp — Vow. V, No. 30.—Jung, 1873. 
