STUDY IV. 171 



It is principally on the fliores of the Ocean that 

 the invifible boundary is fixed, which the Au- 

 thor of Nature has prefcribed to its waves. It is 

 there you perceive, that you are at the interfedlion 

 of two different planes, the one of which termi- 

 nates the declivity of the Land, and the other 

 commences that of the Sea. 



It cannot be alleged, that it was by currents of 

 the Sea the bed was hollowed out ; for where 

 could the earth that filled it before be depofited ? 

 They could raife nothing above their own level. It 

 cannot even be alleged, that the channels of rivers 

 have been excavated by the current of their own 

 ftreams, for there are feveral which have found a 

 fubterraneous paflage through maffes of folid rock, 

 fo hard and fo thick, as to bid defiance to the 

 pick-axes and the mattocks of our labourers. Be- 

 fides, on the fuppofition which we are examining, 

 thefe rivers muft have formed, at the place of their 

 falling into the Ocean, banks of fand, and accu- 

 mulations of earthy fubftances, of a magnitude pro- 

 portional to the quantity of ground which they 

 muft have cleared away, in forming their channels. 

 Moft of them, on the contrary, as has been already 

 obferved, empty themfelvesat the bottom of bays, 

 hollowed for the exprefs purpofe of receiving 

 them. 



How 



