The Evolution of Climates. — Manso/i. \\y 
siliferous rocks of the pre-Cambrian and Azoic ages — the bor- 
der land between geology and cosmology. The minerals com- 
posing the rocks of these earlier ages like those of later ages, 
are presumably worked over materials of previous ages, the 
traces of which are buried beneath the strata of all subsequent 
time* and a study of which carries us into the pre-geological 
ages of cosmology. 
We are taught alike in the text-books of the common 
schools and in the profound treatises of geologists and physi- 
cists that during these ages, the earth "was a melted fiery ball, 
surrounded by a thick atmosphere of gases and vapors. In 
the course of ages this fiery ball cooled ofif, and the solid crust 
of rock wrinkled and cracked and was thrown into ridges and 
valleys." 
"Meanwhile the waters condensed and ran into the hol- 
lows. The interior is still hot but the crust is now so thick 
that but little of the interior heat escapes. The present heat 
of the surface is derived almost entirely from the sun."f 
Of this stage of the earth's climatic development. Sir. A. 
Geikie says: "At an early period in the earth's history, the 
water now forming the ocean, together with the rivers, lakes 
and snow-fields of the land, existed as vapor, in which were 
mingled many other gases and vapors, the whole forming a 
vast atmosphere surrounding the still intensely hot globe."]; 
We therefore accept the view that the first recorded period 
of the history of a planet is one during which its own interior 
*It is well to note here that of the total land area less than 3 per 
cent is covered by lava, or molten materials from which the heat has 
partially escaped by conductivity. Beneath these lava covered areas 
lie all strata antedating the Quaternary period. From but a small 
fraction of the known geological strata has the earth heat finally 
escaped except by denudation. How far beneath present limits of 
geological investigation these worked over materials form the crust of 
the earth is a matter of conjecture — yet elaborate and profound 
mathematical calculations of the duration of earth heat are based 
upon the loss of that heat by "the thermal conductivity of rock 
masses" and the "rate of increased heat toward ilie earth's center." 
And largely upon these calculations is based the idea that earth heat 
by reason of being shut up beneath a non-conducting crust could not 
have sensibly affected surface temperatures. 
tThis quotation is introduced from an elementary textbook on 
Physical Geography. Warren's New Physical Geography, p. 11. Ed- 
ited by Dr. Wm. H. Brewer of Yale. 
tText Book of Geology, p. 33. Sir A. Geikie, London, 1882. See 
also Essays, Prof. T. S. Hunt, p. 40. 
