On the north side of Lake Ontario, southwest of the Canadian city of Kingston, is a lake situated on a height of land one side of which forms a cliff. It is just south of the arm of Lake Ontario known as Quinte Bay and it stands 180 feet above the bay. There is no opportunity for surface waters to flow into this little lake and no one has the slightest idea whence it derives its waters, which are clear and fresh. The lake is about one and a half miles long with a width of about three-quarters of a mile. Mr. A. T. Drummond recently wrote a letter to _Nature_, in which he said he believed he had solved the mystery of the invisible inflow, which cannot possibly be attributed to springs from any higher ground in the neighborhood. In his opinion the source of the lake is to be found in the Trenton limestone area some twenty-five or thirty miles to the northeast. There is a steady rise in these rocks to the north and their dip is favorable to sending the water that sinks through the soil to them southward to the region of Lake Ontario. Fifty miles away the rocks have a height of 400 feet above the lake. In order to ascertain the bearing of these rocks upon the origin of the inflow, Mr. Drummond last summer made a series of soundings in the little lake. The largest part of the lake is shallow, but along its southern edge he found a great rent in the bottom nearly a mile long and a third of a mile wide. In this rent the depths varied from seventy-five to 100 feet. He says the rent is probably due to a wide fault or breakage in the Trenton limestone, and he believes that the same forces that gave rise to this fault may account for a subterranean connection with the higher ground many miles to the north through which the water finds its way into the little lake that overlooks Ontario. Mr. Drummond’s theory is the most plausible that has yet been suggested to account for the source from which this mysterious lake receives its waters. A BOILING LAKE.