22 BEPOBT— 1886. 



Bonney has directed attention to the evidence of the existence of 

 this land as far back as the Trias, while Mr. Starkie Gardner has 

 insisted on connecting links to the sonthward as evidenced by fossil 

 plants. So late as the Post-Glacial, or early human period, large tracts 

 now submerged formed portions of the continents. On the other 

 hand the internal plains of America and Europe were often submerged. 

 Such submergences are indicated by the great limestones of the Paleo- 

 zoic, by the chalk and its representative beds in the Cretaceous, by the 

 Nummulitic formation in the Eocene, and lastly by the great Pleistocene 

 submergence, one of the most remarkable of all, one in which nearl}^ the 

 whole northern hemisphere participated, and which was probably sepa- 

 rated from the present time by only a few thousands of years.' These 

 submergences and elevations were not always alike on the two sides of 

 the Atlantic. The Salina period of the Silurian, for example, and the 

 Jurassic, show continental elevation in America not shared by Europe. 

 The great subsidences of the Cretaceous and the Eocene wei'e proportion- 

 ally deeper and wider on the eastern continent, and this and the direction 

 of the land being from north to south cause more ancient forms of life to 

 survive in America. These elevations and submergences of the plateaus 

 alternated with the periods of mountain-making plication, which was 

 going on at intervals at the close of the Eozoic, at the beginning of the 

 Cambrian, at the close of the Siluro-Cambrian, in the Permian, and in 

 Europe and Western America in the Tertiary. The series of changes, 

 however, affecting all these areas was of a highly complex character, and 

 embraces the whole physical history of the geological ages. 



We may note here that the unconformities caused by these move- 

 ments and by subsequent denudation constitute what Le Conte has called 

 ' lost intervals,' one of the most important of which is supposed to have 

 occurred at the end of the Eozoic. It is to be observed, however, that as 

 every such movement is followed by a gradual subsidence, the seeming 

 loss is caused merely by the overlapping of the successive beds deposited. 

 We may also note a fact which I have long ago insisted on,^ the regn- 

 lar pulsations of the continental areas, giving us alternations in each 

 great system of formations of deep-sea and shallow- water beds, so that 

 the successive groups of formations may be divided into triplets of shal- 

 low-water, deep-water, and shallow-water strata, alternating in each 

 period. This law of succession applies more particularly to the forma- 

 tions of the continental plateaus, rather than to those of the ocean margins, 

 and it shows that, intervening between the great movements of plication, 

 there were subsidences of those plateaus, or elevations of the sea-bottom, 



' The recent surveys of the Falls of Niagara coincide with a great many evidences 

 to which I have elsewhere referred in proving that the Pleistocene submergence of 

 America and Europe came to an end not more than ten thousand years ago, and was 

 itself not of very great duration. Thus in Pleistocene times the land must have been 

 submerged and re-elevated in a very rapid manner 



* Arcadian Geology, 1865. 



