FORM OF THE CONTINENTS— WATTS IgQ 



It became necessary for him to replace or supplement oscillations 

 of the earth crust by a world-wide periodic ebb and flow of the 

 oceans, to and from the continents; positive movements of trans- 

 gression carrying the sea and its deposits over the lands, drowning 

 them and their features under tens or hundreds of fathoms of water ; 

 and negative movements or regressions when the oceans retreated 

 to the deeps, leaving the continents bare or encrusted with recently 

 formed sediments. 



Although the facts cried out for this generalization Suess was at 

 a loss to supply any mechanism competent to produce the wonderful 

 rhythm. The problem was difficult because a liquid must maintain 

 a horizontal, i. e., an equipotential, surface. It was manifestly im- 

 possible to withdraw from the earth, and later to replace upon it, the 

 vast quantity of water that would be required ; and, though a shifted 

 water level, or even a varied water surface relative to the continents, 

 might be caused by polar ice caps, by redistribution of the continents 

 carrying their local effects on gravitation, by variations in the rate of 

 the earth's rotation, or other far-reaching causes, none of these would 

 Fupply an explanation that fitted all the facts. Regressions of the 

 sea could be to some extent explained if Suess's main postulate, that 

 the great ocean basins had been slowly sinking throughout geo- 

 logical time, were granted. But this explanation only rendered 

 more impotent the raising of ocean levels by deposits of sediment, 

 and this was almost the only valid cause for transgressions that he 

 had been able to suggest. 



Further, it is not possible to ignore the definite relationship that 

 exists between the pulsation of the oceans and the raising of moun- 

 tains by lateral or tangential stress. Periods of positive movement 

 or advance of the seas were times of comparative tranquillity, when 

 tangential pressure was in abeyance. Periods of negative movement 

 and retreat were invariably marked by the operation of great stresses 

 by which the earth's face was ridged and wrinkled in the throes of 

 mountain birth. 



The theory that continuous cooling and shrinkage of the interior 

 of the earth afforded an explanation of mountain ranges and other 

 rugosities on its surface was a legacy from the nebular hypothesis. 

 In spite of the homely simile of a shriveling apple, this explanation 

 has never received a very enthusiastic welcome from geologists, 

 though, in default of other resources, they had to make use of it. 

 As knowledge has grown the difficulties have become insurmountable 

 to them. 



First, there is its inadequacy to explain the vast amount of lateral 

 movement required to account for the greater mountain ranges; 

 their rocks, originally spread over a wider area, having been folded 



