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DYNAMICAL GEOLOGY. 



areas, times of great precipitation to alternate with times of prevailing 

 drought ; times of full lakes and of large hard-working rivers, with 

 times of dwindled or feeble waters ; times favoring the wide distribu- 

 tion of forests and abundant vegetation with times of lessening forests 

 and widening barrens, and of exterminations among both vegetable 

 and animal species. All attempts therefore to find, in the results of 

 aqueous action, a definite measure of any part of the geological past 

 are necessarily futile ; as another has recently said, " it is the duty of 

 geologists to point out the impossibility of correlating historical and 

 geological time." 



7. Accordance with the Universal Law of Progress. — The general 

 law at the basis of all development is strikingly exhibited in the 

 earth's physical progress. The law is simply this : Unity evolving 

 multiplicity of parts, through successive individualizations, proceeding 

 from the more fundamental onward. 



The earth in igneous fusion had no more distinction of parts than a 

 germ. Afterward, 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 ex- 

 panded, 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 continents 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 extent ; and the continents 

 were throughout covered with streams at work, channeling mountains, 

 spreading out plains, opening lines of communication, and distributing 

 fertility everywhere. 



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

 final diversity, has been shown to exemplify in many ways the same 

 great principle. 



Thus the earth's features and functions were successively individ- 

 ualized, — first, the more fundamental qualities, and finally, those 

 myriad details in which its special characteristics, its magnificent per- 

 fection, and its great purpose of existence and fitness for duty, largely 

 consist. 



