252 



CHANGES SINCE THE TERTIARY PERIOD. 



[Ch. XII. 



I was anxious, even in the title of this map, to guard the 

 reader against the supposition that it was intended to repre- 

 sent the state of the physical geography of part of Europe at 

 any one point of time. The difficulty, or rather the impossi- 

 bility, of restoring the geography of the globe as it may have 

 existed at any former period, especially a remote one, consists 

 in this, that we can only point out where part of the sea has 

 been turned into land, and are almost always unable to de- 



termine what land may 



All maps, there- 



fore, pretending to represent the geography of remote geo- 

 logical epochs must be to a great extent ideal. The map 

 under consideration is not a restoration of a former state of 

 things, at any particular moment of time, but a synoptical 

 view of a certain amount of one kind of chai 

 sion of sea into land) known to have been brought about 

 within a given period. 



The vertical movements to which the land is subject in 

 certain regions, consist of the alternate subsidence and up- 

 rising of the surface ; and by such oscillations at successive 

 periods, a great area may have been entirely covered with 



vhole may never have been 



marine 



time 



tive proportion of land and sea may have continued unaltered 

 throughout the whole period. I believe, however, that since 

 the commencement of the Tertiary period, the dry land in 

 the northern hemisphere has been continually on the increase, 

 both because it is now greatly in excess beyond the average 

 proportion which land generally bears to water on the globe, 



and because a 



compar 



son of the Secondary and Tertiary 

 strata affords indications of a passage from the condition of an 

 ocean interspersed with islands to that of a large continent. 

 But supposing it were possible to represent all the vicissi- 

 tudes in the distribution of land and sea that have occurred 

 during the Tertiary period, and to exhibit not only the actual 

 existence of land where there was once sea, but also the ex- 

 tent of surface now submerged which may once have been 

 land, the map would still fail to express all the important 

 revolutions in physical geography which have taken place 

 within the epoch under consideration. For the oscillations 





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