120 THE RELATIVE POSITION OF THE [Ch. VII. 



divided into two parts by the slate which ascends very near to 

 the summit even of Kit Hill, the highest part of this range : 

 and one of the projecting granitic hills near Redruth is said 

 to be separated from the main mass by a narrow and shallow 

 band of slate, which passes over the concave curve south of 

 that town. 



Thus we learn how difficult it is, even in a country compara- 

 tively so well known as Cornwall, to trace the precise bound- 

 aries of the rocks, since even the distinctly characterized 

 granite and slate cannot be accurately laid down, unless mi- 

 nutely examined step by step. It is, therefore, very probable 

 that every succeeding enquirer will find the granitic masses 

 of Cornwall more penetrated and intersected by slate than his 

 predecessor. This circumstance, combined with the facts, 

 that the thin and superficial portions of slate are often com- 

 pletely disintegrated, and therefore subject to be obliterated 

 by the next current of water which may pass over them ; and 

 that in many primary districts the granite is almost entirely 

 concealed, only appearing here and there in small conical 

 masses, which, in consequence of their greater durability, must 

 increase in extent by the progressive removal of the adjacent 

 decomposing slates resulting from the action of the elements ; 

 all these things tend to indicate that the granitic masses were, 

 at one time, more extensively enveloped in slate than at pre- 

 sent; and to render it probable that they were originally 

 entirely surrounded thereby, and that therefore their present 

 protrusion must, in some measure, be attributed to the subse- 

 quent decay and removal of the stratified rocks by the 

 operation of causes now in action. 



This explanation of the relative position of these rocks is, 

 however, only considered as applicable to the more recent and 

 subordinate changes which have taken place : but this subject 

 will be discussed hereafter ; we must, for the present, confine 

 ourselves to a description of the situation of these rocks near 

 their junction. 



" The mountain of Lugnaquilla, in the east of Ireland," says 



