84 bulletin: museum of comparative zoology. 



further details concerning the African Permian sea it is possible to 

 admit a shallow sea in the Atlantic area as far north in that district 

 as the southern tropic, but this at a later stage than the epoch of 

 principal glaciation in x\frica. Both in Africa and South America, 

 the marine beds of the Permian demand land near sea-level immedi- 

 ately before and after the invasion by the sea. Little else can at 

 present be argued from their occurrence. 



The volcanic islands which stake out the mesial line of the Atlantic 

 and its connection with the Arctic Ocean hug the shores of Europe 

 and Africa rather than those of the Americas. Since those volcanoes 

 whose substructure is known are associated with crustal displacement 

 involving either horizontal or vertical motion or both and particularly 

 the latter mode of derangement, it is probable that we see in these 

 islands the indirect evidences of a geologically recent movement of the 

 Atlantic bottom which we know from Iceland was well under way in 

 Miocene times. Along the shores of North and South America which 

 trend northeast and southwest we find traces of downsinking of the 

 land in Cretaceous times. In the North Atlantic region, the Pan- 

 Appalachian mountain-chain extending from the dislocated structures 

 of the Rocky Mountains across the southern United States to the 

 coast in Newfoundland can be traced north of the Alps in Europe 

 into Asia but is interrupted in the Mississippi embayment and by the 

 North Atlantic basin which cuts across the folded structures as if they 

 had sunk to form the present ocean floor. These and other indicated 

 changes of depth and outline of the Atlantic province make it in- 

 credible that in Permian times the basin had much of its present 

 length, breadth, and depth. We may conclude therefore that the 

 geologist is free to converge the coasts of Africa and South America in 

 Permian and earlier Carboniferous time as closely as any biological 

 facts and geological evidences of land may demand for their explana- 

 tion. 



In south Brazil all the known facts from the Atlantic border demand 

 an extension of land beyond the present coast in late Palaeozoic time, 

 but how far towards the coast of Africa we can not say. The dis- 

 covery of the Gondwana flora in the Falkland Islands makes it possible 

 to effect the distribution of these plants from .\ustralia into South 

 America by way of the Antarctic continent. Possibly Africa also 

 received its population by this route or more likely from India. 

 The revealing of the geology of the Antarctic continent receives from 

 this state of the problem of Gondwana-land a renewed interest. 



The Permian Glacial Problem.— In the foregoing account of the 



