It cannot be affirmed that on the whole the second region has a higher mean annual temperature than the first, or Atlantic. The further advance towards the north of certain plants on the western side of the Alleghanys, depends partly on the nature of those plants and partly on the different distribution through the seasons of the year of the same annual amount of heat. The broad valley of the Mississippi enjoys, at its northern extremity, the warming influence of the Canadian lakes, and at the south, that of the Mexican Gulf-Stream. These five lakes (Lakes Superior, Michigan, Huron, Erie, and Ontario,) cover an area of 92,000 square miles. The climate is so much milder and more uniform in the vicinity of the lakes, that at Niagara, for instance (in 43° 15′ north lat.), the mean annual winter temperature is only half a degree below the freezing-point, whilst, at a distance from the lakes, in 44° 53′ north lat. at Fort Snelling, near the confluence of the river St. Peter with the Mississippi, the mean winter temperature is 15°.8 Fahr.[EB] At this distance from the Canadian lakes, whose surface is from five to upwards of six hundred feet _above_ the sea’s level, whilst the bottom of Lakes Michigan and Huron is five hundred feet _below_ it, recent observations have shown that the climate of the country possesses the actual continental character of 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 on the Atlantic side.” At Fort Gibson, on the Arkansas river, which falls into the Mississippi, in lat. 35° 47′, where the mean annual temperature hardly equals that of Gibraltar, the thermometer was observed, in August, 1834, to rise to 117° Fahr. when in the shade, and without any reflected heat from the ground.