28 HISTORICAL GEOLOGY 



signified an awful catastrophe (physical and organic) which devas- 

 tated the earth and destroyed all organisms, after which came a 

 period of tranquillity when a new set of organisms was created. 

 This has been called the doctrine of catastrophism. In opposition 

 to this view Sir C. Lyell promulgated the doctrine of uniformita- 

 rianism which holds that the evolution of the earth and its in- 

 habitants has progressed practically uniformly, and that missing 

 records in one place are to be found in other places. Today 

 Lyell's view is generally accepted with the modification that times 

 of comparatively more rapid earth disturbance, and probably 

 changes in organisms, have occurred. 



Trangressions and Retrogressions of the Sea 



During our study of the clearly recorded portion of the earth's 

 history we shall find positive evidence of repeated transgressions 

 and retrogressions of marine waters over various portions of what 

 are now the continental areas. Since subsidences or elevations 

 of the lands are not the only known causes of sea transgressions 

 and retrogressions, we shall, in the following pages, refer to sub- 

 mergences and emergences of the lands unless there is good evi- 

 dence for more specific statement in any case. 



Submergence may be caused either by (1) sinking of the land; 

 (2) rise of the sea; or (3) both together. "Both the lowering of 

 the land and the rise of the sea may be due to gradation, to dias- 

 trophism, or to the two combined. Gradation is perpetual and 

 inevitable where land and sea exist. ... It has been computed that 

 if the earth, in its present condition, were to remain without defor- 

 mation long enough for the continents to be base-leveled, the 

 deposition of the sediments thus derived in the sea would raise the 

 sea-level about 650 feet. This would submerge a large part of 

 the base-leveled land. . . . Base-leveling implies a nearly undis- 

 turbed attitude of the land and sea, and hence in itself favors the 

 view that no great deformation affected the continent while it was 

 going on." * Much submergence of lowlands would take place 

 long before such wide-spread base-leveling had been accomplished. 

 Sinking of the land (see below) would of course cause submergence, 

 but whether submergence of the land, in any given case, has been 



1 Chamberlin and Salisbury: College Geology, p. 479. 



