MATERIALS OF THE EARTH. 65 



admit of any dispute ; were we even to admit that 

 the unstratified rocks, which every thing in their 

 nature proves to have been originally irregular, had 

 also once formed portions of an universal level. The 

 original forms thus produced by the elevations of the 

 strata and the protrusion of the unstratified rocks, 

 have indeed been modified by the action of running 

 waters, and often to a great extent ; and thus only 

 can rivers be said to have generated their present 

 beds and the valleys through which they now flow. 

 A very slender consideration of a state of things so 

 obviously necessary, might have saved pages of use- 

 less, and often, of sufficiently acrimonious discussion. 

 In thus giving a general sketch of the distribution 

 of strata, and of their different elevations and posi- 

 tions, as influencing the forms of land, it is yet neces- 

 sary to remark, that these, hitherto distinguished into 

 antient and recent, or primary and secondary, are, in 

 some parts of the world, followed by a third set, 

 which have been produced under peculiar circum- 

 stances. These, indeed, are distinctly divisible into 

 two, arising from two distinct sources ; the one 

 having been formed after the secondary strata, in the 

 basins of antient lakes and in sestuaries, and the 

 others elevated from the bottom of the sea by the 

 power of volcanoes, producing islands or portions of 

 continents. 



Volcanic products form the last, and are among the 

 most recent of the rocks on the surface of the globe ; 

 though differing much in point of antiquity, and being, 

 even now, formed under our eyes. These are, inva- 

 riably, independent productions, although widely 

 scattered over the surface of the earth. 



Veins formed of rock, are either independent, or 

 VOL. i F 



