CONTINENTAL CREEP 359 



peared is that of Wegener. In this hypothesis the crust of the earth is 

 viewed in mnch the same way as in the Taylor hypothesis and is con- 

 cluded to have moved freely for enormous distances. The direction of 

 movement, according to AVegener, was from east to west instead of Tay- 

 lor's north to south movement. While Taylor appealed to the outlines 

 of Greenland to show separation of the mobile from the stationary crust, 

 Wegener cites the shape of the western coastline of the Atlantic as com- 

 pared with its eastern coast as an indication that the western hemisphere 

 parted company from Europe and Africa and slid westward some 2,000 

 or 3,000 miles. The resemblance of outline on opposite shores of the 

 Atlantic has been noted for centuries, but it is very crude and general 

 and its discrepancies in detail are so huge — 700 miles in the ISTorth At- 

 lantic, for instance — that its value as evidence must be very slight. Be- 

 fore it can be accepted as any kind of proof it must be shown that there 

 is no other explanation of the similarity. 



Wegener's conception of the relations of land and sea is as follows : 

 The continents consist mainly of masses of light rocks, sial, resting on a 

 lower mass of heavy rocks, sima, which form a sort of shell beneath the 

 seas and the continents. The rigid sial is supposed to be pulled over the 

 yielding sima towards the equator by gravity acting on sial. In moving 

 equatorward the continents acquire a westward lag or drift as they pass 

 into belts of higher speed of revolution. 



The reader may well wonder why the continents are not all near the 

 equator, after some hundreds of millions of years of this process, instead 

 of occupying their actual positions away from the equator. Yet the 

 continents could not escape the equator in the end, because there would 

 be no westward lag at all unless there were first some actual motion 

 toward the equator. The combined movement must, therefore, have 

 some southerly component which could end only at the equator. It is 

 also questionable whether there would be any westward lag. If the south- 

 erly movement were rapid there would, of course, be a lag, but the motion 

 must have been very slow, as the forces were very slight, and the entry 

 of inertia and friction into the equation might well overcome all the 

 tendency to lag. 



The force called on to produce the southward motion is the slight pull 

 of gravity on the protuberance of the continental sial over the sima. 

 This has recently been calculated by Lambert from the respective densi- 

 ties and found to cause a horizontal pull of one millionth of an atmos- 

 phere. In his opinion, this amount should be between one million and 

 one hundred million atmospheres in order to be effective. 



XXIV — Bull. Geol. Soc. Am., Vol. 34, 1922 



