SUMMARY OF THEORIES 363 



injurious results. It further indicates the wisdom of the selection of 

 central Africa as the site of the Garden of Eden. 



The hypothesis of a change in rate of revolution must account for a 

 probable lateral shortening of the crust of about 10 per cent, according 

 to W. B. Taylor. This would necessitate an enormously higher initial 

 speed, such that the day would have been only four hours long. If, for 

 the sake of argument, this were granted in the case of the Tertiary fold- 

 ing, what would be left of the day, for a similar change would be re- 

 quired for the Carboniferous, and still other changes for the Precam- 

 brian ? The hypothesis advocated by W. B. Taylor in 1885 (slower revo- 

 lution and raising of the poles) depends on this very factor. Postulating 

 an increased revolution, F. B. Taylor, in 1909, attributed to it an east- 

 west belt of folding around the world with the motion southward from 

 the north pole. W. B. Taylor, however, attributes a set of north-south 

 folds greatest near the equator. Chamberlin sees, as a consequence of 

 such a factor, north and south folds near the equator and also tension 

 cracks near the pole, and concludes from the absence of such phenomena 

 that the slowing down has not affected mountain-building. Willis fig- 

 ures an outward thrust from the oceans in all directions against the . 

 continents. 



Hobbs views the same outlines of the Tertiary ranges as Taylor, and 

 concludes that the motion was northward, directly the opposite of Tay- 

 lor's conclusion. Taylor supports his conclusion by the pattern of the 

 •Greenland and near-by coastlines; these, he thinks, show a separation of 

 500 to 1,000 miles, the movement being southward from the polar area. 



Wegener, reasoning from similar features — that is, coastlines which 

 have a rough similarity of outline — postulates that what is now the 

 Western Hemisphere moved westward from 2,000 to 3,000 miles. This 

 motion, according to him, was progressive from the Paleozoic to the 

 present time. Geologists can not believe, however, that the continents 

 should have slid for thousands of miles during the Quaternary and have 

 left no record in the attitude and character of the sediments. Even if 

 the minute forces appealed to by Wegener did become operative, their 

 pull would have been southward toward the equator and not westward 

 along it. Thus Wegener sees certain outlines resulting from westward 

 continental movements, while Taylor sees them resulting from south- 

 ward movements. In both cases the facts can be explained as well or 

 better in other ways. No attempt is made to explain why the sial of 

 Africa did not feel the pull of gravity. 



Another great obstacle which must be overcome by all of these theories, 

 and particularly by those of continental creep, is that of friction due to 



