648 THE ANCIENT LAKES OF WESTERN AMERICA : 
period in the history of our continent, and that geologically 
speaking quite recent, the region under consideration was 
thickly set with lakes, some of which were of larger size 
and greater depth than the great fresh-water lakes which now 
lie upon our northern frontier. Between these lakes were 
areas of dry land covered with a luxuriant and beautiful 
vegetation, and inhabited by herds of elephants and other 
great mammals, such as could only inhabit a well-watered 
and fertile country. In the streams flowing into these lakes, 
and in the lakes themselves, were great numbers of fishes 
and mollusks of species, which, like the others I have enu- 
merated, have now disappeared. At that time, as now, the 
great lakes formed evaporating surfaces, which produced 
showers that vivified all their shores. Every year, however, 
saw something removed from the barriers over which their 
surplus water flowed to the sea and, in the lapse of time, 
they were drained to the dregs. In the Klamath lakes, and 
in San Francisco, San Pablo and Suisun bays, we have the 
last remnants of these great bodies of water; while the 
drainage of the Columbia lakes has been so complete, that 
in some instances, the streams which traverse their old basins 
have cut two thousand feet into the sediments which accumu- 
lated beneath their waters. 
The history of this old lake country, as it is recorded in 
the alternations of strata which accumulated at the bottoms 
of its water basins, will be found to be full of interest. For 
while these strata furnish evidence that there were long in- 
tervals when peace and quiet prevailed over this region, and 
animal and vegetable life flourished as they now do nowhere 
on the continent, they also prove that this quiet was at times 
disturbed by the most violent volcanic eruptions, from 4 
number of distinct centres of action, but especially from the 
great craters which crowned the summit of the Sierra Ne- 
vada. From these came showers of ashes which must have 
covered the land and filled the water so as to destroy im- 
mense numbers of the inhabitants of both. These ashes 
