QUATERNARY AGE. — RECENT PERIOD. 561 



sequence of this elevation. Terraces exist along the St. Lawrence, 

 Lake Champlain, the coast of Maine, and other parts of the North 

 American coast excepting its more southern portions ; and these were 

 a consequence of the changes of level, and are testimony as to the 

 amount of this change. The evidences of a Champlain depression be- 

 low the present level (p. 550) are evidences that an elevation of the 

 same amount has since taken place. 



This elevation made important changes in American Geography. 

 The Arctic, Labrador, and New England coasts gained mucli in extent, 

 and so also some parts of the Pacific border. Nova Scotia became 

 again part of the main land. The beds of rivers flowing south had 

 their pitch increased to its present amount. The river channels with- 

 in tidal limits were excavated to a deeper level, corresponding more or 

 less closely with the amount of elevation in the region ; and this ex- 

 cavation, as already explained, gave additional height to the bordering 

 terraces. Many lakes were drained that had been made by the north- 

 ward depression of the land, thus carrying forward the drying of the 

 continent that was commenced with the subsiding of the flood. 



In Europe, the elevation of which the terraces are testimony appears to have ended 

 in a second Glacial epoch. Marks of this epoch may yet be deciphered in America. The 

 destruction of the Elephant or Mammoth of Champlain America, and of the great Sloth- 

 like beasts and their cotemporaries mentioned beyond, may have been a consequence of 

 it. But the Mastodon and some other Champlain species probably survived into the 

 later part of the Recent period. 



On the coast of Maine, there are large Indian shell heaps of the common Clam ( Venus 

 mercenaria, the Qualwg of the Indians) and, in some places, of the Virginia Oyster, spe- 

 cies which are now nearly extinct on that cold-water coast. As made known by Verrill, 

 there is a colony of living southern species in Quahog Bay, near Bath (twenty miles east 

 of Portland), among which are Venus mercenaria Linn., Modiola plicatula Lam., Ilya- 

 nassa obsoleta Stimp , Urosnlpynx cinerea Stimp., Crepiduh fornicnta Lam., Asterias 

 arenicoh Stimp., Eupagurus longicarpus Edw., and others, reminding one strongly, as 

 Verrill says, of the coast fauna of New Haven, on Long Island Sound; and the Venus, 

 llyanassa, Modioli, and other species occur also in Northumberland Straits, in the 

 southern part of the Gulf of St. Lawrence. At the mouth of Damariscotta River, thirty 

 miles east of Portland, there is the only locality of the living oyster north of Massa- 

 chusetts Bay. Shells of Oysters, Clams, and Scallops (the southern Pecten irradians 

 Lam.) are abundant in the deeper portions of the mud of the harbor of Portland, 

 These species are relics of a past abundant southern population; none of the shells are 

 found in elevated beaches; and hence the migration from south of Cape Cod took place 

 in tho Recent period. Such a migration, extending to the St. Lawrence Gulf, was not 

 possible, unless the Labrador current had first been turned aside; and a closing of the 

 Straits of Bellisle would have brought this about. This implies an elevation of about 

 two hundred feet; and it may be that the one which introduced the Recent period car- 

 ried the continent, to the north, to tins height above the present level. Such an event 

 would have been in harmony with the occurrence of a second Glacial epoch. 



m. Recent Period in Europe and Great Britain. 



The fact of a second Glacial epoch, which is still under discussion, 

 is urged by Swiss geologists and others of Europe. The evidence of 



