MESOZOIC AND CENOZOIC GEOGRAPHY 471 
growth and volcanic action continued, and the land rose 
higher and higher, while lakes that had been seas dur- 
ing the Cretaceous, were completely enclosed by moun- 
tain barriers. During this time the west was the seat 
of many extensive lakes, in which beds of sediment 
were accumulated. In these, records of animal and 
plant life of the times were preserved, so that from them 
we gain a rather clear knowledge of the life that then 
peopled the earth. Some of these lake beds, which were 
of course deposited in horizontal layers, are now found 
folded and tilted in mountain ranges, of which they 
form a part. Hence we may be certain, that after 
the lakes were formed, mountain development tilted 
and drained them, and built their beds into folds. 
It is probable that this series of changes represents the normal 
mode of development of mountains in the sea. At first a chain, 
like that of the Aleutian islands, rises out of the water as a series 
of peaks. The next stage finds the islands more numerous and 
larger, as in the case of Japan, while between the folds there are 
‘arms of the sea enclosed, as we find in the East Indies. The next 
stage in the development has transformed those open arms of the | 
ocean to nearly closed seas, like the Mediterranean. A very shght 
additional change would cut off the sea entirely, elevate the arm 
above sea-level, and change it to a fresh-water lake. 
The Tertiary volcanoes were remarkably abundant 
and active. Thousands of cones, in all stages of de- 
struction, are now seen dotting the plateaus and moun- 
tains of the west (p. 330), and scores of thousands of 
