

SUCCESSIVE STAGES IN THE EARTH'S PROGRESS. 739 



by the waters of the ocean, — especially if the crust beneath the 

 ocean were originally thinner than the continental portion, as may 

 be inferred from its being the portion which subsided most during 

 the earth's contraction. A small change in the ocean would have 

 produced great effects over the globe, through the oceanic currents. 



The cooling of the climate of the earth is probably due to all 

 three of these causes ; but the exact effect of each in bringing 

 about the result, it is impossible, in the present state of science, to 

 estimate. 



3. Progress in the earth accords -with the universal law of 

 development. — The general law at the basis of all development is 

 strikingly exhibited in the earth's physical progress, as has been 

 well shown by Guyot. The law is simply this : — Unity evolving 

 multiplicity of parts through successive individualizations, proceed- 

 ing from the more fundamental onward (see page 599). 



The earth in igneous fusion had no more distinction of parts 

 than a germ. Afterwards, the continents, while still beneath the 

 waters, began to take shape. Then, as the seas deepened, the first 

 dry land appeared, low, barren, and lifeless. Under slow intestine 

 movements and the concurrent action of the enveloping waters, 

 the dry land expanded, strata formed, and, as these processes 

 went on, mountains by degrees rose, each in its appointed place. 

 Finally, in the last stage of the development, the Alps, Pyrenees, 

 and other heights received their majestic dimensions, and the con- 

 tinents were finished to their very borders. 



Again, as to the history of fresh waters. The first waters were 

 all salt, and the oceans one, the waters sweeping around the 

 sphere in an almost unbroken tide. Fresh waters left their mark 

 only in a rain-drop impression. 'Then the rising lands commenced 

 to mark out the great seas, and the incipient continents were at 

 times spread with fresh-water marshes, into which rills were flowing 

 from the slopes around. As the mountains enlarged, the rills 

 changed to rivers, till at last the rivers also were of majestic ex- 

 tent, and the continents were throughout covered with streams 

 at work channelling mountains, spreading out plains, opening lines 

 of communication, and distributing fertility everywhere. 



Again, the first climates were all tropical. But, when mountains 

 and streams were attaining their growth, a diversity of climate 

 (essential to the full strength of the latter) was gradually evolved, 

 until winter had settled about the poles as well as the earth's 

 loftier summits, leaving only a limited zone — and that with many 

 variations — to perpetual summer. 



The organic history of the earth, from its primal simplicity to 



