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Show 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 Mountains, 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 reduced 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 Volney. These meteorological stations or observatories extend from the point of Florida and Thompson'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 oflongitude of 40°. It cannot be affirmed that, on the whole, the mean annual temperature of the second or middle region is higher than that of the first or Atlantic region. The further advance of certain plants towards the north, on the west of the Alleghany mountains, depends partly on the nature of those plants, and partly on the different distribution 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° 53'1 at the confluence of the river St. Peter's with the Mississippi, the mean winter temperature of Fort Snelling is-7°.2 Reaumur, 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 600-530 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 |