398 THE LA W OF EVOLUTION CONCLUDED. 



periodic winds, caused by the varied heating of wide tracts 

 of land at different seasons. Rhythmical motions of a con- 

 stant and simple kind, were, by increasing multiformity of 

 the Earth's surface, differentiated into an involved com- 

 bination of constant and recurrent rhythmical motions, 

 joined with smaller motions that are irregular. 



Parallel changes must have taken place in the motions of 

 water. On a thin crust, admitting of but small elevations 

 and depressions, and therefore of but small lakes and seas, 

 none beyond small local circulations were possible. But 

 along with the formation of continents and oceans, came the 

 vast movements of water from warm latitudes to cold and 

 from cold to warm movements increasing in amount, in 

 definiteness, and in variety of distribution, as the fea- 

 tures of the Earth's surface became larger and more con- 

 trasted. The like holds with drainage waters. 

 The tricklings of insignficant streams over narrow pieces of 

 land, were once the only motions of such waters ; but as fast 

 as wide areas came into existence, the motions of many tribu- 

 taries became massed into the motions of great rivers; and 

 instead of motions very much alike, there arose motions con- 

 siderably varied. 



Nor can we well doubt that the movements in the 

 Earth's crust itself, have presented an analogous progress. 

 Small, numerous, local, and very much like one another, 

 while the crust was thin, the elevations and subsidences 

 must, as the crust thickened, have extended over larger 

 areas, must have continued for longer eras in the same 

 directions, and must have been made more unlike in differ- 

 ent regions by local differences of structure in the crust. 



142. In organisms the advance towards a more inte- 

 grated, heterogeneous, and definite distribution of the re- 

 tained motion, which accompanies the advance towards a 

 more integrated, heterogeneous, and definite distribution of 

 the component matter, is mainly what we understand as the 



