SCIENTIFIC LITERATURE. 



439 



SCIENTIFIC LITEEATUEE. 



GEOLOGY. 

 In accordance with the general re- 

 sults of Mr. G. K. Gilbert's investiga- 

 tion of recent earth movements in the 

 Great Lakes region — that the whole dis- 

 trict is being lifted on one side or de- 

 pressed on the other, so that its plane 

 is bodily canted toward the south- 

 southwest, and that the rate of change 

 is such that the two ends of a line one 

 hundred miles long, running in a south- 

 southwest direction, are relatively dis- 

 placed four tenths of a foot in one hun- 

 dred years — certain general conse- 

 quences ensue. The waters of each 

 lake are gradually rising on the south- 

 ern and western shores, or falling on 

 the northern and eastern shores, or 

 both. This change is not directly ab- 

 vious, because masked by temporary 

 changes due to inequalities of rainfall 

 and evaporation and various other 

 causes, but it affects the mean height 

 of the lake surface. In Lake Ontario 

 the water is advancing on all shores, the 

 rate at any place being proportional to 

 its distance from the isobase through 

 the outlet. At Hamilton and Port Dal- 

 housie it amounts to six inches in a 

 century. The water also advances on 

 all shores of Lake Erie, most rapidly at 

 Toledo and Sandusky, where the change 

 is eight or nine inches a century. All 

 about Lake Huron the water is fall- 

 ing, most rapidly at the north and 

 northeast; at Mackinac the rate is six 

 inches, and at the mouth of French Riv- 

 er ten inches a century. On Lake Su- 

 perior the isobase of the outlet cuts the 

 shore at the international boundary; 

 the water is advancing on the American 

 shore, and sinking on the Canadian. At 

 Duluth the advance is six inches, and 

 at Huron Bay the recession is five inches 

 a century. The shores of Lake Michi- 

 gan are divided by the Port Huron iso- 

 base. North of Oconto and Manistee 



the water is falling; south of these 

 places it is rising, the rate at Milwau- 

 kee being five or six inches a century, 

 and at Chicago nine or ten inches. 

 Eventually, unless a dam is erected to 

 prevent it, Lake Michigan will again 

 overflow to the Illinois River, its dis- 

 charge occupying the channel carved by 

 the outlet of a Pleistocene glacial lake. 

 The summit in that channel is now 

 about eight 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 dis- 

 charge of the Niagara will be intermit- 

 tent, 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 Are- 

 quipa Railroad, Peru, to Lake Titicaca. 

 That remarkable sheet of water is four- 

 teen times the size of the Lake of Gen- 

 eva and twelve thousand feet above the 

 sea, and might be regarded as the rem- 

 nant 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 



