OF ROCKS. 247 



under water. In the mountains of granite and 

 porphyry, there are also precipices and cliffs, the 

 formation of which cannot be attributed to any 

 known cause that can act above the level of the 

 sea. They cannot have been produced by the 

 action of water that has fallen in rain, or in any 

 way run in streams; because there is not only 

 now no water at all equal to the producing of the 

 effect which we see, but there is no channel in 

 which water could at any time have run. Many 

 of our highest mountains those which overtop 

 all the country round have horse-shoe precipices 

 in their sides (often in the north-east side), the 

 tops of which are higher than any thing within 

 many miles ; and therefore we cannot suppose 

 them to have been formed by the action of water 

 above the level of the sea, unless on the absurd 

 supposition that the water ran up one side of the 

 mountain for no other imaginable purpose than 

 that it might run down the other that it acted 

 contrary to the law of gravitation on one side of 

 the summit, just in order that it might the more 

 readily and effectually obey that law on the other 

 side. 



Even in plainer cases than that those in which 

 there is only a gradually inclining dell, with a 

 rivulet meandering along we cannot give the 

 rivulet the merit of making the dell, at least not 

 out of the hard strata of primary rock ; because, 

 unless we have the dell at the beginning, we can- 

 not explain why there is a rivulet there; even 

 rivulets, if they are to be permanent, must have 

 permanent causes; and, unless where there is a 

 spring supplied with water from a store farther up, 

 the sloping sides of the dell are necessary to pro- 



