78 THE WANDERINGS OF ANIMALS [OH. 



was allowed as the utmost speculative limit of sub- 

 sidence. Two or three miles, the average depth of 

 the oceans, seems enormous, and yet it is as nothing 

 in comparison with the size of the earth. On a clay 

 model globe ten feet in diameter the highest moun- 

 tains would be smaller than the unavoidable grains 

 in the glazed surface of our model. There are but 

 few countries which have not been submerged at 

 some time or other, and most of the great chains of 

 mountains, Andes, Rockies, Pyrenees, Alps, Himalayas, 

 are only of Tertiary date. 



Many attempts have been made to construct maps 

 purporting to show the configuration of laud and 

 water at various epochs. Although the results by no 

 means tally with each other, owing to the lamentable 

 deficiencies of geological and fossil data, the hypo- 

 thetical results are sure to be corrective and supple- 

 mentary ; the problems will be solved, since they are 

 not imaginary. The bolder the outlines are drawn, the 

 better, whilst the insertion of detail and the clinging 

 to present coasts give such maps a fallacious look 

 of certainty. Further, when we draw a broad belt of 

 land across an ocean, this belt need never have 

 existed in its entirety at any one time. The features 

 of dispersal intended to be explained by it, would be 

 accomplished just as well by an unknown number 

 of islands which have joined here, whilst others have 

 subsided elsewhere ; like a pontoon-bridge which may 



