Notwithstanding its being fed by so many rivers, Lake Superior has but one outlet by the Straits of St. Mary. At the upper end of these straits, there is a rapid which cannot be ascended, but has sometimes been descended, although the descent requires both skill and caution, and perhaps not a little good fortune. A canal has been cut by the North-West Company, along the northern banks, for the purpose of facilitating their commerce, and they have here a considerable establishment; but their chief fort and storehouses are situated at Kamenestiquia, on the banks of a river which flows into Lake Superior, on the north-west side, and affords an easy communication with the interior. The Strait of St. Mary, it is supposed, does not discharge one tenth of the waters which the lake receives from its numerous rivers; part of the remainder escapes by evaporation, but how the whole is discharged is yet a secret. It does not appear, however, that an exact calculation has hitherto been made, either of the quantity discharged or the quantity received. This lake lies between forty-six and fifty degrees north latitude, and eighty-four and ninety-three degrees west longitude. _Lake Huron_, into which you enter by the Straits of St. Mary, is next in magnitude to Lake Superior. It lies between forty-three and forty-six degrees north latitude, and between eighty and eighty-five degrees west longitude; in shape it is nearly triangular, and its circumference is about a thousand miles. On the Canada side of this lake is an island one hundred miles in length, and no more than eight in breadth; it is called Manataulin, signifying a place of spirits, and is considered as sacred by the native Indians. About the middle of the south-west side of the lake is Saginaw Bay, about eighty miles in length, and twenty broad; Thunder Bay, so called from the continual thunder heard there, lies about half way between Saginaw Bay and the north-west corner of the lake: it is about nine miles across either way. The fish are the same as in Lake Superior. The promontory that separates this lake from Lake Michigan is a vast plain, more than one hundred miles long, and varying from ten to fifteen miles in breadth. At the north-east corner, this lake communicates with Lake Michigan by the Straits of Michilimackinac. It is very remarkable, that although there is no daily flood or ebb to be perceived in the waters of these straits, yet from an exact attention to their state, a periodical alteration in them has been discovered. It has been observed that they rise by gradual, but almost imperceptible degrees, till in seven years and a half they had reached the height of about three feet; and in the same space of time they gradually fell to their former state; so that in fifteen years they had completed this revolution. This, however, is not well established.[19]