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 Mississipi 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 neighbourhood 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 Mississipi, 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, p. 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 shewn the climate of the country to possess a proper continental character, _i. e._, hotter summers and colder winters. “It is proved,” says Forry, “by our thermometrical data, that the climate west of the Alleghany Chain is more excessive than that of the Atlantic side.” At Fort Gibson, on the Arkansas River which falls into the Mississipi in lat. 35° 47′, with a mean annual temperature hardly equal to that of Gibraltar, the thermometer in the shade, and without any reflected heat from the ground, has been seen, in August 1834, to rise to 37°.7 Reaumur, or 117° Fahrenheit.