Ill LECTURES ON EVOLUTION 71 



millions or in billions of years. For my purpose, 

 the determination of its absolute duration is 

 wholly unessential. But that the time was enor- 

 mous there can be no question. 



It results from the simplest methods of inter- 

 pretation, that leaving out of view certain patches 

 of metamorphosed rocks, and certain volcanic 

 products, all that is now dry land has once been 

 at the bottom of the waters. It is perfectly 

 certain that, at a comparatively recent period 

 of the world's history the Cretaceous epoch 

 none of the great physical features which at 

 present mark the surface of the globe existed, 

 It is certain that the Rocky Mountains were not. 

 It is certain that the Himalaya Mountains were 

 not. It is certain that the Alps and the Pyrenees 

 had no existence. The evidence is of the plainest 

 possible character, and is simply this : We find 

 raised up on the flanks of these mountains, ele- 

 vated by the forces of upheaval which have given 

 rise to them, masses of Cretaceous rock which 

 formed the bottom of the sea before those moun- 

 tains existed. It is therefore clear that the 

 elevatory forces which gave rise to the mountains 

 operated subsequently to the Cretaceous epoch ; 

 and that the mountains themselves are largely 

 made up of the materials deposited in the sea 

 which once occupied their place. As we go back 

 in time, we meet with constant alternations of 

 sea and land, of estuary and open ocean ; and, 



