566 PHYSICAL GEOGRAPHY. 



occurring on the coast north of New York, are found in the interior, dis- 

 tributed as follows: Lower St. Lawrence waters, five; Lake Ontario, 

 nine ; salt region of western New York, seventeen ; Lake Erie, seven- 

 teen; Lake Huron, twelve; Lake Michigan, fourteen; Lake Superior, 

 fifteen; Minnesota, seven; Hudson river, only one; Lake Champlain, 

 three; and Hudson's bay, three. 



Theory. The proper explanation of the distribution of maritime plants 

 has been already shadowed forth in the comments of Messrs. Paine and 

 Drummond. Following the glacial period, geologists believe the land of 

 northern America has been submerged several hundred feet, as shown 

 by the remains of marine animals. Along our coast this submergence 

 exceeded one hundred feet. The proof of this statement will be given 

 under the head of Surface Geology. The St. Lawrence valley has 

 yielded marine shells at the height of 470 feet at Montreal, and at 

 somewhat lower elevations in Ontario. When the St. Lawrence valley 

 was thus covered by salt water, the maritime plants would naturally 

 creep along the shore ; and thus may be explained with certainty their 

 introduction as far as the basin of Lake Ontario. So far, the explana- 

 tion must be satisfactory, especially since no conclusions are involved 

 that cannot be legitimately drawn from other sources. 



If the theory is valid, it may be used to account for the introduction 

 of maritime plants along Lakes Erie, Michigan, Huron, and Superior, 

 and it is difficult otherwise to understand how they could have made 

 their appearance in Minnesota. But Lake Superior is surrounded by 

 terraces up to 330 feet, or 968 feet above the ocean. It is agreed that 

 these terraces indicate former levels of water; and that the period of 

 submergence was essentially coeval with that of depression along the 

 sea border indicated by the fossils. The inference therefore seems 

 legitimate that these high terraces were formed beneath the salt water 

 which introduced the plants. If so, an argument is afforded of a sub- 

 mergence of the land about the great lakes of about one thousand feet. 

 Fossil shells of the Champlain age have been found at the height of 

 1000 feet, on Cornwallis and Beechey islands in Arctic America; and it 

 may be that the depression of the land was uniform over all the northern 

 part of our continent at this time. But at present the arguments from 

 the distribution of the maritime plants and the supposed requirements 



