VOL. LXXXI.] PHILOSOPHICAL TRANSACTIONS. 17 



whole western side of our island has probably been raised by the basal tes on which 

 the superficial strata now rest, though from particular circumstances the fused 

 mass has now and then crystallized into granite ; and as it has been conjectured, 

 that the basaltes of Ireland once joined that of the Scotch isles and the main land 

 itself, so perhaps the basaltes of North Wales joined the Irish coast till the sea 

 worked its way or broke in, and destroyed the continuation. As limestone is 

 sometimes said to rest immediately on granite, so at the foot of the Wrekin, and 

 at Lilleshall Hill, no slate is interposed between the limestone and basaltes ; so 

 that the analogy extends even to the exceptions. 



But another series has been observed, which seems to connect granite by a 

 closer tie with the operations of subterraneous fire. In Italy lava stands to slate 

 and limestone in the same relation as granite and whinstone in other countries. 

 Whole ridges of mountains in the Venetian territory consist of solid lava, some- 

 times almost bare, sometimes retaining the super-incumbent strata, with several 

 local variations ; all of which are reducible to a greater or less degree of lifting 

 force. These chains have a totally different form from the common conical shape 

 of volcanos or heaps of loose ejected matters. They seem to afford a clear in- 

 stance of the manner in which long continuations of mountains have been ele- 

 vated ; for it is not easy to admit the supposition of the observer, who has so ac- 

 curately described them, that the limestone has been converted into lava ; and 

 that the ridges existed, such as they appear at this day, before this change was 

 produced by subterraneous fire. Chemical and mechanical considerations are un- 

 Jfavourable to this hypothesis ; and " since most of these branches, whether ma- 

 rine, volcanic, or mixed, preserve nearly the same external characters, directions, 

 and parallelism ;" it appears highly probable, that they have not pre-existed as 

 hills in another state, but owe their elevation to the expansive force of fire ; and 

 that the same lava which appears in so many places lies also under all the lime- 

 stone hills, of which indeed there are evident indications. 



Several modern travellers have described the strata of granite mountains ; but 

 neither in their descriptions nor drawings do we find satisfactory evidence of this 

 arrangement ; nor do we observe it in nature. A liquid mass swelled by heat 

 must crack in cooling. Granite seems to have cracked most frequently like the 

 basalte en tables ; and these flat masses have been taken for strata. A stratum, 

 consisting of proper materials to form whinstone or granite, may have been ex- 

 posed to the necessary degree of heat, and possibly have undergone this change 

 without much relative local derangement. Should such a stratum be discovered, 

 it would afford no proof of the stratification of the great mountains of granite or 

 shapeless whinstone, which, in consequence of its numerous fissures in all direc- 

 tions, sometimes assumes enough of this appearance to impose on an un- 

 wary eye. 



VOL. XVII. D 



