)4 2 HISTviRY OF 



irmke itself a new channel, but spreads over the adjacent land 

 " Tlius," says he, " men are obliged to direct its course ; or, 

 otherwise. Nature would never have found one." He enume. 

 rates many rivers that are certainly known, from history, to have 

 been dug by men. He alleges, that no salt-water rivers are 

 found, because men did not want salt-water ; and as for salt, 

 that was procurable at less expense than digging a river for it. 

 However, it costs a speculative man but a small expense ot 

 thinking to form such an hypothesis. It may perhaps engrosg 

 the reader's patience to detain him longer upon it. 



Nevertheless, though Philosophy be thus ignorant as to the 

 production of rivers, yet the laws of their motion, and the na- 

 ture of their currents, have been very well explained. The 

 Italians have particularly distinguished themselves in this res- 

 pect ; and it is chiefly to them that we are indebted for the 

 improvement. ' 



All rivers have their source either in mountains, or elevated 

 lakes ;* and it is in their descent from these that they acquire 



1 S. Guglit'lmini della Natura de Fiumi, passim. 

 • Extensive accumulations of water, surrounded on all sides by the 

 land, and having no direct communication with the ocean, or with any sea, are 

 called lakes. Lakes are of four distinct kinds. The first class comprehends 

 those which have no issue, and which do not receive any running water. These 

 pools'are generally very small, and do not merit much attention. Some of 

 these, as the Arendt, in Vieille Marche, are formed by the sinking down of 

 the circumjacent lands : otliers, like the lake Albano, near Rome, appear to 

 be old craters of volcanoes filled with water. The second class consists of 

 those lakes which have an outlet, but whicli do not receive any running 

 water. Such a lake is formed by a spring, or rather by a multitude of springs, 

 which, placed on a lower level in a kind of reservoir, are obliged to fill thai 

 before they find an outlet for their own waters. These lakes are neverthe. 

 less fed by little streams of water, almost invisible, which descend from the 

 surrounding lands, or from subterraneous canals. Some great rivers have 

 lakes of this kind for their source. These lakes are naturally situated on 

 great elevations ; there is one of this kind on Mount Rolando, in Corsica, 

 which is l)29i feet above the level of the sea. The third class of lakes is very 

 numerous, consisting of all such as receive and discharge streams of water. 

 Each of the lakes of this class may be looked upon as forming a basin for 

 receiving the neighbouring waters ; they have in general only one opening, 

 which almost always takes its name from the principal river which flows into 

 it. But it cannot, in strict propriety, be said that thnse rivers traverse the 

 lakes, as their waters mingle with those of the basin over which they are 

 diffusi'd. These lakes have often sources of their own, either near the bor- 

 ders, or in their bottom. There are four or five lakes of this class in North 

 America, which, in point of extent, resemble seas, and which, notwitlisland. 



