36 ON CHANGES IN THE DISPOSITION 



out this wide space, the base varies in height, or un- 

 dulates, so that the lower portions of the sandstone 

 occupy different levels, the summits of all the moun- 

 tains range at an average general height of about 3000 

 feet. Among these, Ben More forms a solid and ex- 

 tensive mass; while Coul beg, Suil veinn, and others, 

 the first a mere peak, are separated by many miles 

 from all the other portions. It is impossible to avoid 

 inferring that a continuous bed of sandstone once 

 covered the whole: the divisions of the strata in these 

 separate mountains corresponding accurately in level, 

 while no instance of a position more angular occurs ; 

 and the summits, every where, bearing the usual marks 

 of waste. They have all therefore been shaped out 

 of a continuous mass; or the intermediate country 

 has been denudated, and that to a great extent. 



This kind of denudation is, in other cases, rendered 

 sensible by the correspondences of peculiar strata, in 

 a particular order, at considerable distances. Thus, 

 at Pittsburgh in Pennsylvania, whatever the cause 

 may there have been, coal is found occupying distant 

 summits, or opposite sides of a valley; but we need 

 not go further than our own islands for a very striking 

 instance of this fact. In Morven, several mountain 

 summits of gneiss are covered with insulated masses, 

 consisting of slender portions of secondary horizontal 

 strata with coal, surmounted by trap; the whole 

 having been evidently connected, before that land to 

 the loss of which they owe their present extraordinary 

 position was removed. 



In other instances, we find indications of similar 

 losses, without such marks of the spaces and depths 

 they once occupied. In such cases, the denudations 

 are sometimes inferred from the absence of the super- 

 ficial strata in a particular district, when they are pre- 



