358 A. KEITH OUTLINES OF APPALACHIAX STRUCTURE 



left between them?. The depth of this hole is now 13,000 feet at the 

 most, which is less than the depth of the Triassic floor in the Connecticut 

 Yalle}^ According to this theor}', the j)resent floor of Baffin Bay must 

 be assumed to be somewhat nearly the floor on which Labrador receded 

 from Greenland. This leaves for the thickness of the moving crust some- 

 thing between two and three miles. In order that this mass should slide 

 southward in response to gravity, either the sliding i^lane must have an 

 angle so high as to be inhibited by other facts, or the rocks of Labrador 

 must have been drawn along from regions where the plane was at a high 

 angle and must have been possessed of a tensile strength such as no rocks 

 are known to possess. In short, the value to the theory of this assumed 

 motion of Labrador is only that of a parallelism in outlines, a relation 

 which may equally well have been produced by other means. Therefore, 

 the relations of Labrador and Greenland, being susceptible of other inter- 

 pretations, do not furnish positive proof. 



No other evidence is given by Taylor in support of this theory, and, 

 in fact, some of the ^evidences of direction of motion are set aside by him 

 as immaterial. His case confessedly rests solely on the great trend lines 

 of the Tertiary system, which phenomena can be explained in other ways 

 and are so explained by geologists. A comT)lete acceptance of Ta^dor's 

 theory involves the acceptance of such extreme conclusions regarding 

 amount of crustal transfer and of areas from which the transfer took 

 place that the theory as it stands can not be accepted. It further in- 

 volves a retardation of the earth's speed of revolution between the Car- 

 boniferous and Tertiary, of which there is no known evidence and for 

 which there is no adequate cause. Retardation and slowing down caused 

 by tidal friction have been appealed to by numerous investigators to 

 change the speed of revolution, but critical examination of tidal effects 

 by competent physicists and mathematicians has led to the conclusion 

 that its probable effect is either nil or exceedingly slight. Therefore, to 

 sum up, it seems that Taylor's theory of sliding of the continents from 

 the North Pole down the hill caused by changing revolution of the earth 

 rests on trend lines, which may be explained in other ways : it requires 

 extravagant motions of enormous masses, it does not provide an adequate 

 place from which they may have moved, and it assigns a cause of which 

 there is no evidence and which probably did not accumulate and exert 

 itself during Mesozoic time. Finally, the mechanism which he suggests 

 +o convert the radial pull of gravity into horizontal motion of the crust 

 for hundreds of thousands of square miles meets in friction an obstacle 

 to its acceptance which appears insurmountable. 



The latest form in which the hypothesis of continental creep has ap- 



