326 GEOLOGICAL CHANGES IN THE 



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 submergence 

 and of floating ice, when the Scandinavian flora, which over- 

 spread 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/' 



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 conjectural rate, 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 that most geologists would be disposed to agree with 

 him. 



On this hypothesis the submergence of Wales to the extent 

 of 1,400 feet, would require 56,000 years; but "taking Prof. 

 Ramsay's estimate of 800 feet more, that elevation being 

 required for the deposition of some of the stratified drift, we 

 must demand an additional period of 32,000 years, amounting 

 in all to 88,000 ; and the same time would be required for 



