Dr. Forry on the Climate of the United States, Sfc. 23 



1. The Noi'thern division. — As this region presents the greatest 

 diversity of physical character, so it exhibits the most marked 

 variety of climate. East of the chain of great lakes, there are 

 several mountain ranges, which, with the exception of a few 

 summits, seldom attain a height of more than 2,500 feet above 

 the level of the sea; and of this elevation, perhaps one half is 

 formed by the table-lands upon which the ridges rest. Above 

 the falls of Niagara, the region of the lakes is elevated 600 to 

 700 feet above the ocean, but there are scarcely any ridges that 

 deserve the name of mountains. This immense tract is, with 

 the exception of the eastern states, nearly altogether in a state of 

 nature, being still covered with its dense primeval forests. But 

 the most striking characteristic in the physical geography of this 

 division, is that produced by its vast lakes or inland seas. We 

 here behold a chain of lakes presenting a superficial area of 

 94,000 square miles, with a mean depth of 1,000 feet in the 

 principal lakes, the details of which have just been given. 



In accordance with the diversity in the physical geography, 

 we find that on the sea-coast of New England, the influence of 

 the ocean modifies the range of the thermometer, thus equalizing 

 the temperature of the seasons. Advancing into the interior, the 

 extreme range of the temperature increases, and the seasons are 

 violently contrasted. Having come within the influence of the 

 great lakes, a climate like that of the sea-board is found ; and 

 proceeding into the region beyond the modifying agency of these 

 inland seas, an excessive climate is again exhibited. And if we 

 continue our route as far as the Pacific Ocean, a climate even 

 more mild and equable than similar parallels in Western Europe, 

 as will be satisfactorily demonstrated, will be presented. The 

 variations of the isotheral and isocheimal curves — the lines of 

 equal summer and of equal winter temperature, as illustrated in 

 Plate I; — thus afford a happy illustration of the equalizing ten- 

 dency of large bodies of water. Hence the former division of the 

 surface of the earth into five zones, as regards its temperature, 

 has been superseded in scientific inquiries, by a more precise 

 arrangement. Places having the same mean annual temperature 

 are connected by isothermal lines, and the spaces between them 

 are called isothermal zones. 



It is thus seen that, notwithstanding the mean annual tempe- 

 rature presents little variation on the same parallels, four striking 



