L A K E 217 are Lake Titicaca and the Desguadero in South America, and Lake Tiberias and the Dead Sea on the Jordan. Distribution of Lakes. Although there are few countries where lakes are entirely absent, still it requires little study to see that they are much more thickly grouped in some places than in others. Of the larger lakes, for instance, we have the remarkable group in North America, which together form the greatest extent of fresh water in the world. A similar group of immense lakes is found in Central Africa : -Lakes Victoria Nyanza and Albert Nyanza, whose overflow waters go to form the Nile ; Lake Tanganyika, at the source of the Congo; and Lake Nyassa, on a tributary to the Zambesi. In Asia the largest fresh water lake is Lake Baikal, on the upper waters of the Lena. All these freshwater lakes of great size are at the sources of large and important rivers ; the salt lakes in which Asia also abounds are at the mouths of large rivers, as the Caspian at the mouth of the Volga, and Aral Sea at the mouth of the Oxus. Passing from the consideration of these larger lakes, which from their size may be considered inland oceans, and which therefore necessarily occur in small number, we find large numbers of lakes of comparatively small dimen sions, and when we consider them attentively we find that they are reducible to a small number of species, and, as in the case of plants and animals, the distribution of these species is regulated chiefly by climate, but also by geolo gical conditions. Perhaps the most important and remark able species of lakes is that to which the Scottish lakes belong. They are generally characterized by occupying long narrow depressions in the valleys of a mountainous country in the neighbourhood of the sea, and in a temperate climate. On the sea-coast, lakes of this character are found in Norway, Scotland, Newfoundland, Canada, the southern extremity of Soutli /Ymerica, and the south end of the middle island of New Zealand ; somewhat removed from the sea we have the Alpine lakes of Switzerland and Tyrol, and the great Italian lakes, all of which display the same features as those of Scotland or of Norway. In many flat countries lakes are extraordinarily abundant, as for instance in the north part of Russia and Finland, in the southern part of Sweden, in the northern parts of Canada, and on a small scale in the Hebrides. Lagoons, found on all low sandy coasts, owe their origin to the shifting of the sand under the influence of the wind and tide. They are found at the mouths of large rivers, as on the Baltic and at the mouth of the Garonne. In volcanic regions lakes are not uncommon, generally of a more or less circular form, and either occupying the site of extinct craters or due to subsidences consequent on volcanic eruptions ; such are the Maare of the Eifel in Germany, and many lakes in Italy and in the Azores. Lakes are not only widely distributed in latitude and longitude, they also occur at all elevations. Indeed, as a certain elevation above the sea produces an effect as regards climate equivalent to a certain increase of latitude, we find lakes existing in the centre of continents, and on high plateaus and mountain ranges, in latitudes where they would be speedily dried up if at the level of the sea, Many of the lakes in Scotland (as Lochs Lomond, Morar, Coruisk), of Norway, of British Columbia, and of southern Chili are raised only by a few feet above the level of the sea, and are separated from it often by only a few hundred yards of land, while in the Cordilleras of South America we have Lake Titicaca 12,500 feet, and in Asia Lake Kokonor 10,500 feet above the sea. Many lakes whose surface is raised high above the level of the sea are so deep that their bottom reaches considerably below that level. Dimensions of Lakes. The principal measurements con nected with a number of lakes in different parts of the world, presented in the following table, will give a more precise idea of the size of the lakes than could be given by description alone : Xame of Lake. Mean Lati tude. Sl O ~A c o a 2 ** e-2 rf Height in Feet al>ovu the Sea of Tempera ture of Water at Hottom. Surface. Hottom. t745 X. 14 N. 1230 X. 12 X. 16 30 S. r t x. VJ X. 16 X. 42 X 3130 X. c s. 40 N. 4625 X. +7 40 X 1 ^ g ( o 5 Miles. 350 320 18 220 90 01 330 280 600 45 330 48 45 35 20 11 23 10 7 14-5 9 4 14-5 2-5 Miles. 100 80 22 48 30 42 40 25 50 10 40 2-5 8-7 8 4 1-5 1-8 1 0-8 1 1 0-8 0-5 0-3 Feet. 978 840 20 204 924 4,080 238 3.600 1,308 1,000 1,356 1,092 394 630 1.020 774 480 480 450 378 330 120 102 627 694 570 564 12.500 io.. c .oo 1,300 72 -85 1.272 -351 -246 + .150 + 360 + 11.576 -2.720 + 166 -3.685 -2,580 -TR6 + 126 +906 -605 - 9flO -724 -887 -116 -60 + 290 +823 +330 + ],2-:s F. 88-8 5PG 44-6 41-7 to 43 . . 39-6 41-4 to 42 40-8 to 41 -4 41-2 to 42 -: 42 to 44 41-4 43-9 43-9 44-7 45-5 53-9 Erie Baikal Uulkash Dead Sea 2,700 670 1,218 1,300 25 30 50 S3 364 390 6C8 1,163 450 1,330 Lomond 1 Katrine Tav Ericlit Garry . . From this table it will be seen that by far the largest continuous sheet of fresh water is the group of North American lakes, and of these Lake Superior is more than double the size of any of the others ; this is principally due to its great breadth, as it is very little longer than Lake Michigan. Lake Superior communicates with Lakes Michigan and Huron, which are really branches of one and the same lake, by the St Mary s river, the fall being 4 ( J feet from Superior to Huron. Huron empties itself into Erie by the St Clair river, Lake St Clair, and finally the Detroit river. Lake Erie overflows by the Niagara river and falls into Lake Ontario, whence the water finally is conveyed to the sea by the St Lawrence. The area of the lakes together is in round numbers 100,000 square miles, and, if that of the St Lawrence and its estuary be added, the water area will be about 150,000 square miles, whih; the whole drainage area is only 537,000 square milet. Hence of the water conveyed by the St Lawrence to the sea, rather more than one-fourth falls on the surface of tin- water itself. Looking to their great extent, we should have- suspected them to be much deeper than is found to be the case. The deepest, Lake Superior, is no deeper than Loch Morar in Inverness-shire. Comparatively shallow, however, as they are, the bottoms of them all, with the exception of Erie, are several hundred feet below the level of the sea. It has been supposed that in former times this chain of lakes formed an arm of the sea similar to the Baltic in Europe, and in support of this view we have the fact of the discovery of marine forms in Lake Michigan. In Asia Lake Baikal is in every way comparable to the great Canadian lakes as regards size. Its area of over 9000 square miles makes it about equal to Erie in super ficial extent, while its enormous depth of over 4000 feet makes the volume of its waters almost equal to that of Lake Superior. Although its surface is 13GO feet above the sea-level, its bottom is 2720 feet below it. A former connexion with the ocean has been claimed for this lake, owing to the fact that seals inhabit its waters. Other large lakes in Asia are mostly salt, and some lie wholly below the level of the sea. Thus the Caspian lies 85 feet below the Black Sea, and the bottom at its greatest depth is 3000 feet deeper. The Dead Sea is over 1300 feet deep, and its surface is 1272 feet below the Mediterranean, so that its bottom is 2580 feet below the level of the sea. In the Caspian seals are found. A former connexion with the Red Sea has been claimed for the Dead Sea, but this XIV. 28
