96 LAKE SUPERIOR. 



nity to make the following remarks on the causes that influence the 

 outlines of continents : 



" The outlines of continents are not to be considered as fixed, immovable 

 limits, but are variable, and dependent upon the degree of elevation above 

 the level of the sea. For instance, were we to depress certain parts of South 

 America or of the United States, even for a few feet, their outlines would be 

 entirely changed, and immense tracts submerged ; and vice versa, a slight 

 elevation would produce corresponding changes. 



" The west of Asia, comprising Palestine and the country about Ararat 

 and the Caspian Sea, &c., is below the level of the ocean, and a rent in the 

 mountain chains by which it is surrounded, would transform it into a vast 

 gulf. 



" Continents are in fact only a patch-work formed by the emergence and 

 subsidence of land. These processes are still going on in various parts of 

 the globe. Wbere the shores of the continent are abrupt and high, the 

 effect produced may be slight ; as in Norway and Sweden, where a gradual 

 elevation is now going on without much alteration of their outlines. But if 

 the continent of North America were to be depressed a thousand feet, 

 nothing would remain of it except a few islands ; and any elevation would 

 add vast tracts to its shores. 



" Elie de Beaumont, who has occupied himself much with tracing the 

 changes wrought in continents by geological phenomena, has shown that 

 chains of mountains elevated at the same time agree in direction. Thus the 

 mountains of Scandinavia, the Ural chain and the Alps, &c. Before the 

 elevation of the Alps, Europe was not divided into two gi'eat chmatic re- 

 gions. In this country the north and south direction of the mountains has 

 a great influence. Animals migrate more extensively, and the cold winds, 

 penetrating further south, influence the temperature. 



" It would be very interesting to ascertain in detail the dependence of 

 the forms of continents on geological phenomena. I have been struck with 

 the possibility of this in running along the shore of this lake. Tbe general 

 shape of Lake Superior is that of a crescent. But it would be a great mis- 

 take to suppose it bounded by curved lines. Its shores are combinations of 

 successive sets of straight parallel lines, determined in each instance by a 

 peculiar system of trap-dykes. These dykes have flve general directions, and 

 the outlines of the shores are determined by their combinations. One of 

 these directions is east, 30° north. This we find in the islands off Prince's 

 Location, in Isle Royale, &c., and then again in Point Keewenaw and White- 

 Fish Point. This is cut across by one east, 20° north : these two we have 



