2,6o THE HISTORY OF CREATION. 



separated and far distant chains of mountains ? It is diffi- 

 cult to believe, and in many cases quite inconceivable, that 

 these inhabitants of fresh water should have in any way, 

 actively or passively, migrated over the land lying between 

 the lakes, or that the inhabitants of mountains in any 

 way, actively or passively, crossed the plains lying between 

 their mountain homes. But here geology comes to our help, 

 as a mighty ally, and completely solves these difficult pro- 

 blems for us. 



The history of the earth's development shows us that the 

 distribution of land and water on its surface is ever and 

 continually changing. In consequence of geological changes 

 of the earth's crust, elevations and depressions of the ground 

 take place everywhere, sometimes more strongly marked in 

 one place, sometimes in another. Even if they happen so 

 slowly that in the course of centuries the seashore rises or 

 sinks only a few inches, or even only a few lines, still they 

 nevertheless effect great results in the course of long periods 

 of time. And long — immeasurably long — periods of time 

 have not been wanting in the earth's history. During the 

 course of many millions of years, ever since organic life ex- 

 isted on the earth, land and water have perpetually struggled 

 for supremacy. Continents and islands have sunk into the 

 sea, and new ones have arisen out of its bosom. Lakes and 

 seas have slowly been raised and dried up, and new water 

 basins have arisen by the sinking of the ground. Peninsulas 

 have become islands by the narrow neck of land which con- 

 nected them with the mainland sinking into the water. 

 The islands of an archipelago have become the peaks of a 

 continuous chain of mountains by the whole floor of their 

 sea being considerably raised. 



