144 Fossil Shells from the Colorado Desert. [ March, 
as periods of convulsive action, recurring cycles of sudden and 
of gradual changes, operating through different but succeeding 
geologic ages or periods of geologic time. Prof. Whitney has 
pointed out the coincidence of mountain peaks of extraordinary 
elevation and areas of extraordinary depression (below the sea 
level), which are a part of the peculiar characteristics and striking 
topographical features of the same general area. 
During the pliocene epoch the site of the present desert was 
occupied by the sea or was, perhaps, a part of the Gulf of Cali- 
fornia. 
* Hediot I7 ss Me Miocene and possibly Pliocene 
fossils are found at the mouth of Kern River cañon, showing that 
the sea then washed freely against the foot of the Sierra; there is 
even reason for believing that it extended far up the Colorado River 
basin; and certainly it deposited a thick bed of the enormous 
Miocene oyster (0. é#¢an), with other remains along the west shore 
1 For most interesting information as to the height of mountains, the depression of 
Death and other seme saline plains, alkaline lakes, mud volcanoes and other phe- 
nomena which mark the physiognomy and relate to the general aspect of this won- 
derful region, attention is directed to Vol. i, Geol. Survey of Cal. (by Prof. Whit- 
ney), also Whitney in Proc. Cal. Acad., Vols. ii, iii eiss iv; Veitch in Vol. i, zd. 
Col. Williamson in Vol. iii, ¿ď.; Cooper in Vol. ., and Liew. Wheeler’s Asta a 
Report for 1876. Another author, Dr, J. P, cenas Groin whose interesting article 
in the Overland pai Poor 1873) I have previously quoted, writes as fol- i 
lows of the do Des 
Crossing om the San se Pass, the continuation of the Sierra Nevada range 
back of San TETA the men leaves e faeije coast mioys po ver 
* the 
and enters upon t appears remains 
of some ancient world As he came ee the. T * pass, upon his right 
towered San Gorgonio Peak, * 7 0,500 feet in a ie the left 
forming the other wall of the pass, pine-clad tis Bernardino eaches 
an altitude of 11,500 feet. But leaving now the mountains behind he descent es 
what seems the scorched, blasted bed of sume old cyclopean furnace 
San Gorgonio and San Bernardino on this side have lost their pines, and brown, barren 
and desolate, frown down upon yet greater desolation. Upon the west * : 
stretch the Sierra in an unending line—a forbidding rugged wall. At the north,a 
spur from this main chain turns off eastward, and then curving around bears to the 
south, parallel to the Sierra, making another abrupt wall, which at last drops down 
and is lost near Fort Yuma, Inclosed by these mountains, open only toward the | 
south, where 200 miles away it faces out upon the waters of the Gulf of Califerste: a 
is the Colorado Dese > 
Surrounded upon euri side by mountains, except in one direction, and there 
opening out upon the head of the Gulf of ake it shows that the desert is a 
portion of the old gulf which then extended 200 miles above its present limit. The 
cause of the separation of the upper end of pas gulf, making what is now the Colo- 
tido I Desert, is so apparent, that a moment’s examination reveals it. The same- 
