116 STEPPES AND DESERTS. 



1, the Atlantic States east of the Alleghanies ; 2, the Western States 

 in the wide basin between the Alleghanies and the Rocky Mount- 

 ains, through which flow the Mississippi, the Ohio, the Arkansas, 

 and the Missouri ; 3, the high plains between the Rocky Mountains, 

 and the Maritime Alps of New California through which the Oregon 

 or Columbia River finds a passage. Since the highly honorable 

 establishment, by John C. Calhoun, of uninterrupted observations of 

 temperature, made on a uniform plan at 35 military posts, and re- 

 duced to daily, monthly, and annual means, we have arrived at more 

 just climatic views than those which were so generally received in 

 the time of Jefferson, Barton, and Yolney. These meteorological 

 stations or observatories extend from the point of Florida and Thomp- 

 son's Island (Key West), lat. 24 33', to the Council Bluffs on the 

 Missouri ; and if we reckon amongst them Fort Vancouver, lat. 45 

 37', they include differences of longitude of 40. 



It cannot be affirmed that, on the whole, the mean annual tem- 

 perature^ of the second or middle region is higher than that of the 

 first or Atlantic region. The further advance ( of certain plants to- 

 wards the north, on the west of the Alleghany mountains, depends 

 partly on the nature of those plants, and partly on the different dis- 

 tribution of the same annual quantity of heat. The wide valley of 

 the Mississippi enjoys at its northern and southern extremities the 

 warming influence of the Canadian Lakes, and of the Mexican Gulf 

 Stream. The five lakes (Superior, Michigan, Huron, Erie, and 

 Ontario) occupy a space of 92,000 English square miles. The 

 climate is much milder and more equable in the neighborhood of 

 the lakes; for example, at Niagara (lat. 43 15') ; the mean winter 

 temperature is only half a degree of Reaumur (1.2 Fahrenheit) 

 below the freezing point, while at a distance from the lakes, in lat. 

 44 53', at the confluence of the river St. Peter's with the Missis- 

 sippi, the mean winter temperature of Fort Snelling is 7. 2 Reau- 

 mur, or 15. 9 Fahrenheit (see Samuel Forry's excellent Memoir on 

 " the Climate of the United States," 1842, pp. 37, 39, and 102). . 

 At this distance from the Canadian \Lakes (whose surface is from 

 500 to 600530 to 640 English feet above the level of the sea, 

 whilst the bottom of the Lakes Michigan and Huron is about five 

 hundred feet below it), recent observations have shown the climate 



