«0 , KEronT~1886. 



the existence of this land as far back as the Trias, while Mr. Slarkie 

 Gardiner lias insisted on connecting links to the southward 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 raost remarkable of all, one in which nearly 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 were 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 forma^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 Silnro- 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 causedjby these movements 

 and by subsequent denudation constitute what Le Conte has called ' lost 

 intervals,' and one of the most iL.portant 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 regu- 

 lar pulsations of the continental areas, giving ns 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. 



But I must here call your attention to still another geological parodox, 

 namely, that the deep sea, which is so great a barrier to the passage of the 

 shallow-water animals, seems, under certain conditions, to afford facilities 

 for the transmission of land animals and plants. The connections esta- 



' 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. 



2 Arcadian Geology, 1865, 



