250 



CHANGES IN THE EAETH'S GEOGRAPHY 



[Ch. XII. 



changes in the height of European lands have occurred- 

 what was formerly the bed of the sea having been raised, 

 together with its marine shells, to elevations of 500 and 

 even 1,400 feet, and corresponding subsidences, attended by 

 the submergence of much ancient land, having taken place 

 within an era so modern in the history of the earth. In 

 one part of this Glacial Period we find proofs that England 

 and Ireland were united to each other, and to the continent, 

 while at other times they were broken up into an archipelago 

 of small islands ; we also find that large parts of Northern 

 Germany, and Russia, were beneath a sea often covered with 

 floating ice ; and that the Desert of the Sahara was under 

 water between lats. 20° and 30°, so that the eastern part 

 of the Mediterranean communicated with that part of the 

 ocean now bounded by the west coast of Africa. The Atlantic 

 also penetrated far into what is now the basin of the St. 

 Lawrence, and the White Mountains in New Hampshire con- 

 stituted an archipelago. In short, a map of the Northern 

 Hemisphere, even in glacial times, would bear but a distant 

 resemblance to our present maps of the same region, and so far 

 as we are acquainted with the geology of equatorial countries, 

 they have undergone an equal amount of alteration. This 

 may be seen by anyone who will consult Darwin's map of 

 coral reefs and active volcanos, which shows how many large 

 areas have been the theatres, some of subsidence, others of 

 elevation on a great scale, while the species of shells and 

 corals of the Atlantic and Pacific have remained unchanged. 

 The continent of South America, from lat. 34° S. to Pata- 

 gonia, appears also to have been upraised throughout its 

 entire width, since the beginning of the Post-tertiary 

 period. The geographical distribution of the quadrupeds, 



Mai 



Mr. Wallace 



union 



of those islands with each other and with the mainland, 

 since the present species were in being. He has shown that 

 the Indian fauna exhibits an abundance of species common to 

 both sides of those straits wherever the depth does not ex- 

 ceed 100 fathoms, whereas if the soundings are deeper, even 



