DIASTROPHISM AND THE FORMATIVE PROCESSES 133 



nized, they do not alter the great fact that the abysmal bottoms are 

 mantled almost universally by a characteristic deposit, nor is there 

 ground to suppose that these inequahties of deposition are sufficient 

 to conceal any great deformation that has affected the abysmal 

 bottoms since the earth came to mature form. Mountain ranges, 

 if they once existed on the sea bottom, can scarcely have been 

 seriously obscured by deep-sea deposits, and, if there have been 

 protrusions from the sea bottom of a continental order, their con- 

 figurations should still be visible. 



Among the characteristics of the deep-sea deposits that have 

 diagnostic value in our study are those especially which imply that 

 given deposits must have been formed at given abysmal depths. 

 There is need to consider the following factors: 



(•i) The rehcs of fife that lived in the surface waters of the 

 clear ocean or within photosynthetic depths or depths that have 

 distinct relations to surface conditions, the pelagic life or plankton. 

 Where the surface life mingled freely with terrigenous silt, as it 

 generally did near extensive land, the silt tells the tale of its rela- 

 tionship. Where the surface life made deposits essentially free from 

 admixture with terrigenous silts, open oceanic conditions are gener- 

 ally implied, blit the deposits in themselves do not imply any special 

 depth of sea. They do not even necessarily imply distance from 

 land, for if the set of the ocean currents is constantly and steadily 

 toward the land, the pure oceanic waters may effectively keep back 

 the land silts and give origin to a pure oceanic deposit close up to 

 land. So too, measurably, if currents of pure oceanic waters set 

 steadily and persistently into mediterranean bodies of water, 

 relatively pure pelagic deposits may be formed when the conditions 

 are such that basal and marginal agitation is held in abeyance. 

 When the land has been well base-leveled and is densely clothed 

 with vegetation and bordered by sea-encroaching plants, the con- 

 ditions are favorable for relatively pure oceanic deposits even in 

 waters that indent or intersect the land. Some of the earher 

 extravagances in the interpretation of chalk deposits have found a 

 check in considerations of this kind. The measure of shallowness 

 of the bottom in such cases is likely to be revealed by the nature 

 of the bottom life. Submerged platforms, however, when isolated 



