Beyond the Ozark mountains, the district between the Red river and the Canadian is occupied by the red sandstone of the salt formation, mentioned when speaking of that region, and is undoubtedly to be considered secondary. How far it extends to the west beyond the sources of Red river and the Canadian, we are unable to determine. At the commencement of the most eastern ridge of the Rocky Mountains, a few south of the high peak, and at no very great distance north from Santa Fé, the boundary again becomes determinate. From this point it runs nearly north one hundred and fifty miles, where it crosses the river Platte. From the narrative of Lewis and Clarke, we are enabled to determine with sufficient accuracy, that it crosses the Missouri not far from the Falls, in longitude 110° west. Beyond this, the little information we have, we owe to Sir Alexander Mackenzie. He informs us, that great quantities of pit coal are found about the sources of the Saskatchawin which lie near the Rocky Mountains, and between 50° and 55° north latitude. The sources of Saskatchawin are placed by this traveller near the base of the Rocky Mountains; and the coal formation which he mentions, lies on the margin of a plain extending far to the north and east. The Saskatchawin running to the east, traverses 15° of longitude, and discharges its waters into Lake Winnipic in {317} latitude 53° north. Lake Winnipic is connected by the Severn and Port Nelson rivers to Hudson's-bay. There is a water communication, interrupted by one portage, from the Saskatchawin, north-west, to the Mississippi or Churchill's river; and from thence, by the Lake of the Hills, Slave Lake, and Mackenzie's river, to the North Sea. Near the Lake of the Hills, in latitude 59°, Mackenzie found several brine springs. This, though not decisive evidence, perhaps justifies the conclusion, that secondary rocks exist in that neighbourhood. A view of the character and direction of the several large rivers which traverse the region about Hudson's Bay, of their numerous inosculations, and the number and position of the small lakes which abound in every part of it, afford, at least, presumptive evidence, that it is an extensive plain little inclined in any direction.