1879. ] Fossil Shells from the Colorado Desert. 149 
sidiary ranges upon its western flank on the other, spreading lat- 
erally as well as in the direction of what may be regarded as the 
great highways furnished by the main stream and its principal 
confluents. 
That we may have a better idea of the Colorado river and its 
tributaries, and of the regions traversed by the latter, I will quote 
the eloquent description of Prof. Powell. 
“There are two distinct portions of the basin of the Colorado. 
The lower third is but a little above the level of the sea, though 
here and there ranges of mountains rise to an altitude of from 
two to six thousand feet. This part of the valley is bounded on 
the north by a line of cliffs, which present a bold e tenn 
step, hundreds or thousands of feet to the table lands a 
e upper portion of the basin rises from four to eight thou- 
sand feet above the level of the sea. This high region on the 
east, north and west, is set with ranges of snow-clad mountains 
attaining an elevation above the sea varying from eight to fourteen 
thousand feet. All winterlong on its mountain crested rim, snow 
falls, filling the gorges, half burying the forests, and covering the 
crags and peaks with a mantle woven by the winds from the waves 
of the sea—a mantle of snow. When the summer sun comes, 
this snow melts, and tumbles down the mountain sides in millions 
of cascades. Ten million cascade brooks unite to form ten thou- 
unite to form the Colorado, which rolls, a mad, turbid stream, 
into the Gulf of California.” 
Anodonta. Owen’s River, Cal, 
While the specimens from Washoe lake are in every feature so- 
close to those from Bear river in the distant Wahsatch range, the 
mussels inhabiting Owen’s river at an elevation of es € on 
