322 



PHYSICAL GEOGRAPHY. 



boats have often been in danger of sinking, and could only be extricated by being towed 

 by lighter boats. As for myself, I have never been in danger of foundering, but I have 

 several times had great difficulty in passing this spot with six stout rowers, whose utmost 

 efforts could scarcely overcome the attraction of the mud. A similar phenomenon is 

 observed on the Lake Saginaga, whose bottom attracts the boats with such force that it 

 is only with the greatest difficulty that a loaded boat can be made to advance : fortunately 

 the spot is only about four hundred yards over." This statement has received confirma- 

 tion from the experience of Captain Back, during the recent arctic land expeditions. A 

 part of Lake Huron, likewise, in the same district, appears to be the centre of a remarkable 

 electrical attraction. There is a bay in the lake, over which the atmosphere is constantly 

 highly charged with electricity, and it has been affirmed that no person has ever traversed 

 it without hearing peals of thunder. 



Lakes differ greatly in their colour, clearness, and depth. It is difficult to account in 

 every case for the tints of water. They are referable to a variety of causes. The 

 geological character of the beds of lakes, of the surrounding objects from which shadows 

 are cast, and of the soil drained by them ; their depth, with the nature and quantity of 

 the subaqueous vegetation, have influence in determining the colour of their waters. 

 Those of the Great Bear Lake are a beautiful light blue, especially in the vicinity of the 

 primitive mountains of M'Tavish Bay, where they are very transparent. A piece of white 

 rag, when sunk here, did not disappear till it had descended to the depth of ninety feet. 

 This remarkable transparency belongs to the waters of Lake Superior, which are so 

 pellucid that the fish and rocks are distinctly visible at most extraordinary depths. 

 Those of Lake Huron also are brilliantly crystalline ; and to a voyager on some of the 

 Scandinavian lakes., the density of the medium on which he is floating appears little 

 greater than that of the atmosphere. So completely are the senses here sometimes 

 deceived, that the stranger has recoiled in involuntary alarm from his situation, impressed 

 with the idea of being about to be precipitated among the rocks and chasms disclosed 

 below him. " Nothing," says Elliot, in his letters from the north of Europe, " appears 

 more singular to a foreigner than the transparency & the waters of the Norwegian lakes. 

 At the depth of 100 or 120 feet the surface of the ground beneath is perfectly visible ; 

 sometimes it may be seen wholly covered with shells, sometimes only sprinkled with 

 them ; now a submarine forest presents itself to view, and now a subaqueous mountain." 

 A farthing has been seen at the depth of 120 feet in Lake Wetter in Sweden. The 

 depth of lakes, of which a few examples are given below, is very various ; and all efforts 

 to sound some have failed, owing to the line running out without reaching the bottom. 



Greatest Soundings. 



Feet. 



Lough Neagh - - 102 



Killarney - - - 252 



Lomond, average depth 120 feet 720 



Ness - 810 



Constance - 2334 



Geneva, medium depth 560 - 900 



Neuchatel 



Lucerne 



Zurich 



Maggiore 



Como 



Iseo 



426 



600 



600 



2625 



1698 



984 



Garda 



Nemi 



Wetter 



Wena, average depth 240 



Moela 



Caspian Sea - 



Superior 



Huron 



Erie - 



Ontario 



Michigan 



Greatest Soundings. 

 Feet. 



951 

 2700 



440 



573 

 66 



2800 

 1200 

 1000 



270 



300 



900 



Some lakes are periodical, their waters retiring into subterranean reservoirs through 

 crevices in their beds, from whence they successively re-issue. This is the case with 



