POST-TERTIARY PERIOD. 553 



origin. The facts prove that the continent, over at least its colder 

 temperate latitudes, was depressed below its present level, and that 

 this depression extended across it from the Atlantic far towards the 

 Rocky Mountains, and existed also west of the mountains over 

 Oregon and California. 



The amount of depression was 30 feet along southern New Eng- 

 land, as proved by the elevated beaches. It was 30 to 50 in north- 

 ern Connecticut, 100 to 170 in Massachusetts, and from 170 to 200 in 

 New Hampshire, as shown by the height of the upper river terrace 

 on the Connecticut above the lower flats. It was 400 feet about 

 Lake Champlain, and 450 or more in the vicinity of Montreal, as 

 indicated by beds containing marine fossils. The upper terraces of 

 the Great Lakes show a like depression in their vicinity, amounting 

 to at least 330 feet on the north shore of Lake Superior. The ele- 

 vated sea-beaches of the Arctic correspond to a depression there of 

 1000 feet in some regions. There was therefore a marked geogra- 

 phical change over the northern latitudes between the Glacial and 

 Champlain epochs, — a change from a condition of elevation, in which 

 the sea-border lay outside of its present limits, to one of depression, in 

 which the ocean encroached again on the land, making Lake Cham- 

 plain and the St. Lawrence, for a long distance, arms of the sea. 



The subsidence may have affected the southern part of the United 

 States and earned the continent there eight or ten feet below its 

 present level. The evidence is not satisfactory on this point. On 

 the Pacific side of the continent the subsidence amounted to some 

 hundreds of feet. It is probable that the auriferous gravel of 

 California was made from the pre-existing rocks and distributed 

 over the hills and valleys during the Glacial and Champlain epochs. 



Sea-beaches mark the presence of the sea in so many places about New Eng- 

 land and Canada that we admit at once the conclusion they suggest. And, 

 being so common to the height mentioned, we certainly have abundant reason 

 for doubting any depression of the continent beyond this extent. Hence, the 

 submergence in the Glacial period of 4000 or 5000 feet, required to meet the 

 necessities of the Iceberg theory, may well be pronounced altogether im- 

 probable. 



Climate. — (1.) Temperature of the sea. — In consequence of the de- 

 pression of the continent making an extended gulf of the river St. 

 Lawrence, the Labrador or polar current (p. 41) would have carried 

 its waters and temperature westward beyond Montreal. As the 

 species of shells in the elevated beaches are all such as inhabit the 

 present coasts from the Arctic to Maine, the temperature of the 

 waters must have been essentially the same as now. By reference 

 to the Physiographic Chart, it will be seen that the North Frigid tern- 



