EXCURSIONS OF AN EVOLUTIONIST 



the earth. The greatest physical geologists now 

 living, however, such as Mr. Croll and the 

 brothers Geikie, are convinced that there has 

 been no considerable change in the positions of 

 the great oceans from the very beginning ; and 

 this view is ably sustained by Mr. Wallace 

 who is probably the highest living authority on 

 the distribution of plants and animals in his 

 profound and fascinating treatise on " Island 

 Life," lately published. 



Though the general relative positions of deep 

 sea and continent have not altered, however, 

 there have been frequent and striking changes in 

 the superficial contour of land and sea. Every 

 continent has been several times wholly or in part 

 submerged, while shallow portions of what is now 

 sea-bottom have been thrust up high and dry ; 

 and in this way the climate and the mutual rela- 

 tions of floras and faunas have been variously and 

 vastly affected. Thus, during the Silurian period, 

 the dry land of Europe lay mostly in the north, 

 over Finland, Scandinavia, and the German 

 Ocean, covering also the British Islands, and 

 stretching more than two hundred miles out into 

 the Atlantic. The central and southern parts of 

 Europe were then covered by a shallow sea, with 

 islands on the sites of Bavaria and Bohemia. 

 The duration of this state of things may be dimly 

 imagined when we consider the enormous quan- 

 tity of sediment worn off from this northern con- 



