Scientific Intelligence — Geology. 397 



The Modern Epoch — Reign of Man. — The present epoch suc- 

 ceeds to, but is not a continuation of, the Tertiary age. These 

 two epochs are separated by a great geological event, traces of which 

 we see everywhere around us. The climate of the northern hemi- 

 sphere, which had been, during the Tertiary epoch, considerably 

 warmer than now, so as to allow of the growth of palm-trees in the 

 temperate zone of our time, became much colder at the end of this 

 period, causing the polar glaciers to advance south, much beyond 

 their previous limits. It was this ice, either floating like icebergs, 

 or, as there is still more reason to believe, moving along the ground, 

 like the glaciers of the present day, that, in its movements towards 

 the south, rounded and polished the hardest rocks, and deposited the 

 numerous detached fragments brought from distant localities, which 

 we find everywhere scattered about upon the soil, and which are 

 known under the name of erratics, boulders, or greyheads. This 

 phase of the earth's history has been called by geologists the Glacial 

 or Drift period. 



After the ice that carried the erratics had melted away, the sur- 

 face of North America and the North of Europe was covered by the 

 sea, in consequence of the general subsidence of the continents. It 

 is not until this period that we find, in the deposits known as the 

 diluvial or pleistocene formation, incontestable traces of the species 

 of animals now living. 



It seems, from the latest researches of geologists, that the ani- 

 mals belonging to this period are exclusively marine ; for, as the 

 northern part of both continents was covered to a great depth with 

 water, and only the summits of the mountains were elevated above 

 it, as islands, there was no place in our latitudes where land or fresh- 

 water animals could exist. They appeared, therefore, at a later pe- 

 riod, after the water had again retreated; and as, from the nature 

 of their organization, it is impossible that they should have migrated 

 from other countries, we must conclude that they were created at a 

 more recent period than our marine animals. 



Among these land animals which then made their appearance, 

 there were representatives of all the genera and species now living 

 around us, and besides these, many types now extinct, some of them 

 of a gigantic size, such as the Mastodon, the remains of which are 

 found in the uppermost strata of the earth's surface, and probably 

 the very last large animal which became extinct before the creation 

 of Man. 



It is necessary, therefore, to distinguish the two periods in the 

 history of the animals now living ; one in which the marine ani- 

 mals were created, and a second, during which the land and fresh 

 water animals made their appearance, and, at their head, Man. — 

 (Principles of Zoology by Louis Agassi:: and Augustus A. Goidd, 

 Part i., p. 203.) 



VOL. XLV. NO. XC. — OCTOBER 1848. 2 D 



