Whenever southerly winds prevail--and, in the cycle of the gyration of atmospherical currents, this is certain, and will be reduced to calculation--the great lakes are filled to the edge; and whenever northern and northeasterly winds take their appointed course, then these mediterraneans sink, and the valley of the Mississippi is filled to overflowing. But the most curious facts are, that the different lakes exhibit different phenomena. The Board of Public Works of Ohio states that, in 1837-38, the quantity of water descending from the atmosphere did not exceed one-third of that which was the minimum quantity of several preceding years. Ontario, from the reports of professional persons, has varied not less than eight feet, and Erie about five. Huron and Superior being comparatively unknown, no data are afforded to judge from; but what vast atmospheric agencies must be at work when such wonderful results in the smaller lakes have been made evident! People who live at the Niagara Falls, and I agree with them in observations extending over a period since 1826, believe that these Falls have receded considerably; and, although I do not enter into the mathematical analysis of modern geologists respecting them, as to their constant retrocession, believing that earthquake split open the present channel, yet I have no doubt that the level of Lake Erie is considerably affected by the diminution of the yielding shaly rocks of their foundation. Earthquake, and not retrocession, appears to me, who have had the singular advantage, as a European, of very long residence, to have been the cause of that great chasm which now forms the bed of the Niagara, from the Table Rock to Queenston, in short, a rending or separating of the rocks rather than a wearing; and this is corroborated by the many vestiges of great cataracts which now exist near the Short Hills, the highest summit of the Niagara frontier, between Lakes Erie and Ontario, as well as by the great natural ravine of St. David's. But this is a subject too deep for our present purpose, and so we shall continue to treat of the Great Lakes in another point of view. Chemically considered, these lakes possess peculiar properties, according to their boundaries. Superior is too little known to speak of with certainty--Huron not much better--but Erie, and particularly Ontario, have been well investigated. The waters of these are pure, and impregnated chiefly with aluminous and calcareous matter, giving to the St. Lawrence river a fresh and admirable element and aliment.