NATURAL HISTORY. 45 



ferent parts, twice over the Appenine mountains, and 

 made clivers tours in the environs of these mountains, 

 and in mount Jura, he found that the contours of all 

 mountains hear a striking resemblance to the works of 

 regular fortifications. When the body of the moun- 

 tain runs from east to west, it forms prominences, 

 which face as much as possible to north and south ; 

 tins admirable irregularity is so striking in Tallies, that 

 we seem to walk in a very regular covered way : if, 

 for example, we travel in a valley from north to south, 

 we perceive that the mountain which is on the right 

 forms projections or angles which front the east, and 

 those of the mountain on the left, front the west ; so 

 that, in fact, the prominent and concave angles, on 

 each side, correspond with one another alternately. 

 The angles which mountains form in great vallies are 

 less acute, because the direction is less steep, and as 

 they are farther distant from each other ; and in plains 

 they are not so perceptible as in the course of rivers, 

 which generally take up their elbows ; the middle of 

 them naturally answer to the most striking projections, 

 or the most advanced angles of mountains ; and this 

 is the cause of the serpentine course of rivers. It is 

 astonishing so obvious a fact should have remained so 

 long unobserved, for when in a valley the inclina- 

 tion of one of the mountains which border it, is less 

 steep than that of the other, the river takes its course 

 much nearer the steepest mountain, and does not flow 

 through the middle of the valley. 



These observations might be confirmed by a num- 

 ber of facts. The mountains of Switzerland, for in- 

 stance, are steeper on the south ^iJo than on the north, 

 and on the we.st than on the east side. But the most 

 striking example is afforded by the mountains of 



