EISE OF CHEONOLOGY 493 



the fact that the Permian of Knssia is constituted 01 three series of 

 strata — two zones of mechanically made deposits separated hy a lime- 

 stone — just as is the Triassic of north Europe. The great significance 

 of this announcement was not appreciated by the geologists of the time, 

 and it is probable that even its author did not see its full import. John 

 Strong Newberry, however, read the statement, and after 1860 proposed 

 the theory of "cycles of deposition," an idea which he came to hold largely 

 through his explorations in 1857-1858 with Lieutenant Ives up the Colo- 

 rado Eiver of the West, the region that has inspired so many American 

 geologists, and in 1874 he stated clearly the theory of periodicity of sea 

 invasion. Although we no longer hold so firmly to the theory of cycles 

 of sedimentation, out of it has grown much of our modern conception of 

 periodic diastrophism. In turn, Newberry's writings reacted on the Irish 

 geologist, Hull, who in 1862 applied the theory mainly to the Carbonifer- 

 ous sequence, and in 1872 Godwin Austen directed attention to the fact 

 that "the marine series is again and again interrupted, over large areas, 

 by continental deposits, like the Old Eed sandstone, for instance, the 

 Coal Measures of the Carboniferous system, and the fresh-water deposits 

 of the Weald." 



These ideas came to fruition in Suess (1885-1888), who did not think 

 that the periodic invasions of the sea were necessarily caused by the move- 

 ments of the earth's crustas exemplified in the making of great mountain 

 ranges, for, after all, these are comparatively local and culminate rapidly, 

 while the transgressions are far more widely spread and decidedly slower 

 in attaining their climax. There are, therefore, according to him, "inde- 

 pendent movements of the sea — that is to say, changes in the form of the 

 hydrosphere." In these movements lies the valuable fact of world-wide 

 spread similar events and the possibility of employing almost everywhere 

 the same terminology relating to periods and eras. This general correla- 

 tion would have been impossible if the limits of the periods had not been 

 drawn by natural processes simultaneously in operation over much of the 

 earth's surface. 



PERMANENCY OF CONTINENTS AND OCEANS 



Most of the older geologists held that the continental and oceanic areas 

 had repeatedly changed places, and Lyell taught that all parts of the 

 ocean bottoms had been land. James D. Dana was the first to assail this 

 conclusion, and shortly after his trip around the world with the Wilkes 

 Exploring Expedition announced, in 1846, that the continents and ocean 

 basins have been practically permanent. That the continents are on the 

 whole permanent is proved by the fact that their marine deposits are 

 almost entirely of shallow seas. Where deep-sea formations occur they 



