ACADEMY OF SCIENCES. 127 
The immediate effect of this relief of lateral pressure would be the settling 
down of the broken, folded, and dislocated crust with nearly its full weight 
upon the molten mass of the interior. This would cause the outflows of 
lavas throngh the broken lines, until the fluid and solid portions of the globe 
were balanced according to their relative densities and weights, just as water 
will ascend in the fissures of broken ice to the points of equal weight. It 
would appear from this line of reasoning, that the greatest outflows of lava - 
ought to have occurred where the greatest downward folding took place; and 
this is strongly indicated, if not proved, by the islands of the oceans being 
nearly all of voleanic origin, and the lower flanks and plateaus of the conti- 
nents having the greatest lava outflows. 
While we must admit that the changes of level over large areas of the globe 
were very slow, and extended through long geological periods, we are still 
forced to the conclusion that sudden changes of vast extent have taken place 
at the close of the principal eras. These convulsive movements not only 
changed the relative positions of the land and ocean levels, but also swept 
away all living forms peculiar to the geological age that was terminated by 
such changes. The general results following such violent terminations -of 
geological ages would be— 
Ist. The escape of enormous quantities of interior heat, accompanied by 
great lava outflows along all the principal lines of disturbance. 
2d. The consequent vaporization of large quantities of water, continued 
through the period of disturbance, and until the lavas were cooled and all 
the principal vents of escaping heat were closed. In the earlier geological 
periods, when the average temperature of the earth and atmosphere was 
much higber than it is now, the waters vaporized during periods of volcanic 
or igneous activity would descend in floods of rain; but in later times the 
general temperature became so much reduced by the radiation of heat, and 
the crust of the earth had become thickened to such an extent, that the 
atmospheric temperature was dependeht mainly upon the influence of the sun. 
Under these conditions, the vaporization of the waters by the outflows of 
lava and hot gases, at the close of the tertiary age, would give results greatly 
modified by atmospheric temperature. Near the points of igneous outbreak, 
the lower zones of vapor would descend in floods of rain; but those portions 
of the continents lying east of and remote from the lines of volcanic activity 
would be buried in enormous depths of snow. Prof. Tyndall says, ‘‘To 
produce a glacier, we must first vaporize the waters.’’ I think I have indi- 
cated how the waters were vaporized. The next thing to demonstrate is the 
freezing of the vapors, and their distribution over the continents, especially 
over those portions remote from active igneous disturbances. 
A careful study of the wind currents at this point becomes an essential part 
of the problem to be solved. The currents of the lower portion of the atmos- 
phere are modified in their movements to a great extent by the mountain 
ranges and continents, but their general tendency is toward the west, as 
they approach the equator. The upper currents are more uniform in their 
movements, and they have a general tendency toward the northeast and 
southeast, moving spirally from the equator toward the poles, in curves of 
great length around each hemisphere before the polar regions are reached, 
