76 THE POPULAR SCIENCE MONTHLY. 



and over all the great continents as rapidly as such other portions of 

 the earth became by temperature, climate, and other conditions ready 

 to receive and maintain it ? Is there any one locality answering to 

 these conditions, and yet of which it may be said, in a grander and 

 truer sense than it was said of Rome, that all roads lead to and from 

 it ; not only highways diverging to every part of the world, but with 

 vehicles upon them ; seed-wagons running constantly in the direction 

 of the most favorable distribution and to the remotest parts of the 

 earth ? Any locality so related to the topography of the whole earth 

 as to render such extensive movements of plants and animals from it 

 in all conceivable directions, and to all distances, not only easy and 

 probable, but consistent with their present distribution? Is there 

 anything in similarity of form, anatomy, structure, size, color, food, 

 habits, habitat, longevity, modes of propagation, terms of gestation, 

 and capacity for inter-breeding between certain flora and fauna of the 

 Eastern Continents and the Western, which would suggest that many 

 species and varieties so widely separated might have come originally 

 from the same locality and ancestry ? Are plants and animals always 

 improved, developed, and rendered prolific more by being moved one 

 way than another ? Are the prevailing bottom currents of air and 

 ocean in the direction of such favorable movements ? Are cases of 

 extermination and degeneration the result of a counter-movement, or 

 a failure to make such favorable movements ? 



Many facts and considerations exist and may be presented pointing 

 to a solution of these questions, and fairly answering some of them. 



Let us consider, in the first place, the probable condition of the 

 earth previous to the advent of any sort of life upon its surface. A 

 large portion of those who have formed any intelligent opinions, in 

 the light of modern thought and investigation, upon the subject of 

 cosmogony, believe and hold very firmly that the earth was at one 

 time an intensely hot globe — indeed, a molten mass — and that in the 

 lapse of time it has cooled down by radiation to its present tempera- 

 ture. It is not at all necessary for the purposes of the present inquiry 

 to examine the so-called nebular theory, nor even to ask when or how 

 this globe became so heated, nor to what extent it has now become 

 cooled, nor need we inquire whether the earth is now but a molten 

 mass covered with a comparatively thin crust, or has cooled and hard- 

 ened to its very center. It is important, however, to have it under- 

 stood at the outset that the facts and considerations here presented 

 are addressed to those, and those only, who have reached and adopted 

 the conclusion that this globe, at some time in the process of its forma- 

 tion and development, passed through a fiery ordeal, that the primary 

 rocks are of igneous formation, and that there are many other existing 

 conditions and obvious facts which can not well be accounted for 

 except upon the hypothesis that the whole earth was once a molten 

 mass. 



