124 PROCEEDINGS OF THE CALIFORNIA 
writers on the subject have failed to account, satisfactorily to my mind, for 
the most important facts observed. Many of these theories are based upon 
an assumption of conditions and causes that cannot be maintained by logical 
deductions from the general laws governing the progressive development of 
the planet. 
I will review briefly some of the theories put forth by eminent scientists, by 
which they attempt to account for the great changes in the climate at the 
close of the tertiary age. 
THE FIRST THEORY 
Is, that there occurred a great upheaval of land in the Northern Hemisphere, 
by which the currents of the ocean and of the atmosphere were greatly 
changed or modified, and that this great elevation above the ocean level was 
the primary cause of the change of temperature. This line of reasoning 
appears to me untenable, for the following reasons: Ist. If the elevation of 
the land surface had of itself sufficient influence on the climate to produce 
the Glacial epoch, it ought by the same law to have continued that condition 
until the present time, and to an indefinite period into the future ages. As 
this supposed cause has not been sufficiently potent to continue glacial condi- 
tions, it therefore follows that it was not the primary cause of climatic 
changes, but was merely a modifying influence, in so far as it changed toa 
limited extént the direction of the air currents. 
2d. The thermal effect of the sun’s rays upon land surfaces is much 
greater than upon water surfaces. Hence the atmosphere becomes heated by 
its contact with the land even at great altitudes. The land surface of the 
North American continent will probably not exceed an average altitude above 
sea level of more than two thousand feet. Compare this altitude with the 
different heating power of the sun’s rays upon land and water, and the change 
would in all probability be an increase of atmospheric temperatures. 
3d. The effects of the elevation of the continents would be to largely 
increase the land surfaces, and correspondingly decrease the areas covered by 
water. The interior basins or inland seas would be drained off, the water- 
sheds steepened, so that the surplus rainfall would be rapidly drained into 
narrow, swift-running streams, thus reducing the sources of vapor to very 
narrow limits as compared with the water surfaces in the beginning of the 
tertiary age. It therefore follows that a largely decreased evaporating surface | 
and a correspondingly increased thermal effect of the sun’s heat, could not 
supply the conditions for a continental glacier system. Hence I conclude 
that the elevation of land surface in the Northern Hemisphere was not an 
adequate or primary cause of the Ice period. 
SECOND THEORY. 
Some investigators suppose that, by some means, the relative positions of 
the poles of the earth have been changed, so as to bring the then frozen zone 
jnto the range of the now temperate and tropical latitudes. Asa proof of 
this, they cite the facts that the remains of vegetable and animal life, that are 
