250 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



ABSTRACT OF WEGENER'S HYPOTHESIS 



As Dr. van der Gracht has treated the Wegener hypothesis at 

 length ^ it will not be necessary here to go into it again fully ; all 

 that will be needed is to state briefly the main points of the theory : 



(1) The earth is not a shrinking mass. 



(2) The amount of water on the earth's surface has always been 

 the same. 



(o) Early in the history of the earth there was a thin universal 

 granitic shell which before the Silurian had been thrust and folded 

 into a greatly thickened continent that he calls Pangaea. 



(4) The continental blocks (Pangaea) underwent great hori- 

 zontal drifting movements in the course of geological time, and these 

 presumably continue even to-day. The rifting probably began in 

 Paleozoic time, but it was not until the middle Jurassic that Aus- 

 tralia-Antarctica began to separate and drift southeast. In the early 

 Cretaceous, the Americas began to move westward and finally, in the 

 Pleistocene, Greenland-Newfoundland was separated from Norway 

 and Great Britain. 



(5) The separated continents of to-day, when moved together, 

 working on a globe, fit against one another as do the pieces of a 

 jig-saw puzzle. 



(6) The poles of the earth have in the past slowly wandered 

 about, and in Permian time they were as much as 2,500 miles from 

 their present positions. 



(7) The mountains of the earth are in the main not due to a 

 shrinking earth but to the drifting of the continents, one set arising 

 at the edge of the forward-moving granitic continents where they 

 come against the resisting basaltic shell, as best exemplified by the 

 Cordillera of North America and the Andes of South America; while 

 those of the Euro-Asiatic continents are due to a " striving toward 

 the equator of the continental blocks," namely, the movement toward 

 each other of the Euro-Asiatic mass and the African one. 



(8) Wegener holds firmly to the theory of isostasy, and accord- 

 ingly believes that the land masses, large or small, can not sink and 

 vanish into the heavier basaltic layer. He does away with land 

 bridges across the oceans by uniting all lands into a Pangaea. 



(9) Accordingly, Wegener rejects the theory of the permanency 

 of oceans and continents as we see them to-day. 



3 Theory of Continental Drift, 1928, pp. 1-75. 



