08 GEOLOGY 
two small detached basins, just at the foot of the Rocky mountains, near Fort Si Vrain, on the 
southern fork of the Platte river. 
In the Pacific region the Tertiary rocks occupy a large superficial extent of country; they form 
the sea coast from Puget Sound to the vicinity of Cape Mendocino, and include the w'hole of the 
beautiful valley of the Willammette river, in Oregon. Fartlier south, after crossing the Shasty moun- 
tains, the Tertiary formation is found in the rich and magnificent valley of the rivers Sacramento 
and San Joachin, where it extends as far as Contra Costa, opposite to San Francisco, and forms 
the celebrated Monte Diablo, which belongs entirely to it. The greater part of the Coast Range, 
from Monterey to Santa Barbara, is also formed by it; it continues, passing by San Pedro and 
San Diego, and enters Lower California, where it forms the Cape of San Bartholomeo. On the 
eastern slope of the Sierra Nevada proper — Cajon Pass — a white and red, very massive pud- 
dingstone is found, which belongs to the Miocene epoch. Finally, the Tertiary formation is found 
at the mouth of the Rio Colorado ; it ascends the valley of this river , and occurs at several points 
on the Bill William Fork, and also near Lake Preuss in the Mormon country. 
Quarternary formation. — The Quarternary or Diluvial formation covers almost the whole super- 
ficial extent of the Eastern and Western regions, but in the Central or Rocky mountain region 
this formation is but little developed, and lies scattered at the bottom of the vaUeys. This geo- 
graphical distribution renders it impossible to color this formation on the map; a map devoted to 
the Quarternary strata alone would be necessary, in order to give a true and exact idea of it. On 
the whole line of the coast extending from the mouth of the Hudson river. New York, to the 
mouth of the Rio Grande del Norte, in the gulf of Mexico, ancient sea margins are seen, one hun- 
dred and fifty feet above the actual level of the sea , and containing in beds of sand and clay , shells 
in the fossil state, identical with those now living in those waters. Likewise, in ascending the 
rivers, as for instance the Mississippi, Arkansas, Missouri, Ohio, the Rio Grande del Norte, the 
Rio Pecos, the Si Lawrence, etc., we find in banks from fifty to one hundred and fifty feet above 
their actual level, sand beds containing: Vnio, Anodon , Helix, Planorhis, Pupa, etc., all belonging 
to the same species as those now living in the beds of these rivers. Numerous hones of mam- 
malia are also found in this clay and sand of the Diluvial period , as : Bison antiquus , liqmis Ameri- 
canus , I'apirus Americanus, Elephas Americanus, Mastodon giganteus, Megatherium mirabile , Megalonix Jef- 
fersonii, and Mylodon Harlani. 
In the country north of the 41° of latitude, marked on the map by a line (See: Frontispiece-, 
Limite m&idionale du Terrain erratique du Nord.'), the Diluvial formation of sand and clay covers drift, 
boulders, and polished and striated rocks also belonging to the same formation. This formation, 
called by Agassiz the Ice Period, on account of the agency of the ice in removing the materials 
that compose it, is widely developed; it covers the whole country, and is sometimes from four to 
eight hundred feet thick. 
In California and Oregon the drift is very much developed; it covers all the rocks of the valleys 
of the Coast Range and the Sierra Nevada , and contains the rich golden deposits of the American 
Eldorado. We find too, at nearly all points on the Pacific Coast, ancient sea margins, sixty and 
one hundred feet above the actual level of the sea. 
