feet above the mean level of the lake, and the time before it will be overtopped may be computed. For the mean lake stage such discharge will begin in about one thousand years, and after fifteen hundred years there will be no interruption. In about two thousand years the Illinois River and the Niagara will carry equal portions of the surplus water of the Great Lakes. In twenty-five hundred years the discharge of the Niagara will be intermittent, failing at low stages of the lake, and in thirty-five hundred years there will be no Niagara. The basin of Lake Erie will then be tributary to Lake Huron, the current being reversed in the Detroit and St. Clair channels. _GEOGRAPHY._ Relating to the Royal Geographical Society the story of his exploration of the Bolivian Andes, Sir Martin Conway spoke of his journey by way of the Arequipa Railroad, Peru, to Lake Titicaca. That remarkable sheet of water is fourteen times the size of the Lake of Geneva and twelve thousand feet above the sea, and might be regarded as the remnant of a far greater inland sea, now shrunk away. Driving from Chililaya, he reached the snowy mountain called the Cordillera Real--the backbone of Bolivia--which he had come especially to visit, and in the region of which he spent four months. To the east the mountains fell very rapidly to a low hill country and the fertile valleys that send their waters to the river Beni. On the other side lay a high plateau, at a uniform altitude of from twelve thousand to thirteen thousand feet, from which the tops of low rocky hills here and there emerged. This plateau had obviously been at one time submerged; evidence was plentiful that in ancient times the glaciers enveloped a large part of the slopes that led down to it from the main Cordilleras and reached down many miles farther than now. In the immense pile of _débris_ left by the glaciers deep valleys were afterward cut by the action of water, and into these valleys the glaciers of a second period of advance protruded their snouts, depositing moraines that could still be traced _in situ_ as much as four or five miles below the present limit of the ice. Contrary to the apparently general impression that the peaks of the Cordilleras were volcanic, the author had not been able to find any trace of volcanic action along the axis of the range. The Cordillera Real had been elevated by a great earth movement, and the heart of the range consisted of granites, schists and similar rocks. The whole range might be described as highly mineralized. Gold was found at several points, but the chief auriferous valleys were those on the east side of the range. Just below the snowy mass of Cacaaca on the west was a really enormous vein of tin; and antimony, cobalt and platinum have been found in different parts. The great copper deposits were not in this range, but farther west. The flora of the high regions of the Cordillera Real was apparently sparse, but is probably more abundant in the rainy season.