418 GEOLOGICAL CHANGES 



" First, a continental period, towards the close of which the 

 forest of Cromer flourished ; when the land was at least 500 

 feet above its present level, perhaps much higher, and its 

 extent probably greater than that given in the map, fig. 41." 

 In this map the British Isles, including the Hebrides, Orkneys, 

 and Shetlands, are connected with one another and with the 

 Continent, the whole German Ocean being laid dry. 



" Secondly, a period of submergence, by which the land 

 north of the Thames and Bristol Channel, and that of Ireland, 

 was gradually reduced to such an archipelago as is pictured 

 in map, fig. 40 ; and finally to such a general prevalence of 

 sea as is seen in map, fig. 39, only the tops of the mountains 

 being left above water. This was the period of great submer- 

 gence and of floating ice, when the Scandinavian flora, which 



i 



overspread the lower grounds during the first continental 

 period, may have obtained exclusive possession of the only 

 lands not covered with perpetual snow. 



" Thirdly, a second continental period, when the bed of the 

 glacial sea, with its marine shells and erratic blocks, was laid 

 dry, and when the quantity of land equalled that of the first 

 period." During this period perhaps Spitzbergen, Greenland, 

 Iceland, and the Faroe Islands, received their present vege- 

 tation, the existence of which can hardly be accounted for 

 without a period of continuous or nearly continuous land. 



It is evident that such changes as these would require a 

 great lapse of time. Sir Charles Lyell admits that the average 

 change of 2J feet in a century is a purely arbitrary and con- 

 jectural rate, and that there are cases in which a change of as 

 much as six feet in a century appears to have taken place : 

 still it is in his opinion probable that the rate assumed in a 

 century is, if anything, above the average, and in this I believe 

 most geologists would be disposed to agree with him. On 

 this hypothesis the submergence of Wales, to the extent of 

 1400 feet, would require 56,000 years ; but " taking Prof. 



