ACADEMY OF SCIENCES. 125 
now peculiar to the tropics, are found in abundance in the polar regions of 
our time. By what means a self-balanced rotating globe could change the 
position of its mass, without changing its line of rotation, is not shown by 
the advocates of the theory; and unless the cause of such change can be 
clearly shown by facts that cannot be accounted for in any other way, the 
theory cannot be accepted as even probable. t 
If the general proposition is true, that the earth was originally incandes- 
cent, and has been slowly cooling through past ages by radiation, it follows 
that the conditions for tropical life must have begun near the poles, and 
progressed toward the tropical zone, in harmony with the changes of climate. 
If no violent disturbances of level had taken place, the change would have 
been slow and almost imperceptible; but we know that violent changes in the 
earth’s crust have taken place, and have produced rapid if not sudden 
changes in the temperatures and climates of its surface. These changes 
have been sufficiently violent to destroy the characteristic types of life exist- 
ing at the time, and mark a distinct period in the progress of the globe 
toward its present condition. I therefore conclude that the theory of a 
change of the poles of the earth is not susceptible of proof, and therefore 
unworthy of serious consideration. 
THIRD THEORY. 
Another class of investigators, failing to apprehend the true causes which 
produced the Ice period, have proposed the theory that the solar system, in 
its sweeping circle throngh space, has encountered or passed through frigid 
zones in the stellar spaces that reduced the surface or atmospheric tempera- 
ture to an extent sufficient to give an Ice period to our climate. 
This theory, like the one above considered, has not been proved by any 
well considered facts, neither is it susceptible of proof by any known means 
within reach of human investigators. If this theory were true, the waters of 
the globe would have been frozen where they now are, and could not have 
been transferred to any considerable extent, by evaporation and condensation, 
upon the land surfaces. 
The extinction of life would have been a slow, starving and ‘‘ freezing out’’ 
process, that could in no reasonable way account for the facts of glacial 
times. The conclusion therefore follows, that cosmical influences had nothing 
to do directly, in producing the Glacial epoch at the close of the tertiary age. 
The facts, so far as I have been able to trace them out, all seem to indicate 
that the geological disturbances and volcanic eruptions that occurred at the 
close of the tertiary age, together with the return trade winds, were the only 
causes, ample and sufficient to produce the facts and phenomena of glacial 
times. 
The question then may be asked here: What are the conditions necessary 
to produce a glacial period? The answer is plain and simple: 1st. A folding 
and dislocation of the earth’s crust along great longitudinal lines (N.-S.) 
along the western borders of one or more continents. 2d. The issue of in- 
terior heat, followed by great outflows of lava along such lines of fracture. 3d. 
The local vaporization of the waters of the surface by contact with the lava 
