126 PROCEEDINGS OF THE CALIFORNIA 
outflows and other points of escaping heat. 4th. The ascent of the vapors to 
a height sufficient to penetrate the return trade winds, or upper currents of 
the atmosphere. 5th. The general depression of the ocean beds, and cor- 
responding elevation of the continents, and development of the great mount- 
ain chains of the globe. 
That such conditions and facts did occur at the close of the tertiary age, 
substantially in the order named, is well known to every practical student of 
Geology. That such conditions and facts, in conjunction with the upper 
currents of the atmosphere, were ample of themselves to produce and would 
of necessity cause the glacial epoch, cannot, in my opinion, be seriously 
questioned. 
To bring this subject clearly before the mind, it will be necessary to make 
a brief survey of the physical geography of the continents.during the tertiary 
age. The geological records, so far as science has been able to trace them 
out and interpret their true meaning, show that, in the beginning of the 
tertiary age, the continents over their largest areas presented low, undulating 
surfaces, but slightly raised above the ocean level; that large districts were 
covered by fresh-water lakes and inland seas, some of them at one period 
presenting the forms of life peculiar to marine and brackish waters, and at 
other periods only such living forms as are kuown to exist in fresh water— 
thus proving that slight oscillations of the earth’s surface were sufficient to 
cause the oceans to invade some of the interior basins of the continents and 
fill them with salt water. Hence, in many of the tertiary formations, we 
have presented the various forms of life peculiar to marine, brackish, and 
fresh waters. During the progress of the tertiary times, great changes of level‘ 
were produced over large continental areas, until they became mostly dry 
land. In the later tertiary period, the marine deposits were gradually con- 
fined to the low borders of the continents, and the interior basins became 
filled exclusively with fresh water, and only fresh-water deposits were formed 
in their beds. 
The climate of tertiary times fluctuated from a tropical warmth, that was 
well nigh universal over the globe at the beginnin., to temperate and even 
Arctic cold in the higher latitudes, where great elevations of mountain chains 
occurred in the later periods. At the close of the tertiary age, the disturb- 
ances of the solid crust of the earth were enormous. Great mountain chains 
were elevated on all the continents, accompanied with corresponding de- 
pressions of the ocean beds, thus confining the oceans to narrower limits 
and increasing the land surfaces above the waters. 
This last grand change of land and ocean levels must have occurred mainly 
by sudden convulsions and re-adjustments of the earth’s crust. The con- 
tinued radiation of heat from the fluid nucleus of the globe caused its con- 
tinued shrinkage. The consolidated crust conformed to this shrinkage by 
corrugations and oscillations of level. The sinking down of the ocean beds 
and elevation of the continents went on slowly through the long periods of 
the tertiary age, until the lateral pressure of the earth’s crust became so great 
that it culminated in a series of dislocations an uplifts over all the conti- 
nents of the globe. The ocean beds were doubtless equally disturbed and 
broken, so as to relieve the. lateral pressure caused by the shrinkage of the 
interior. 
