445 



We will Inquire into the materials from which this fuperficial cover- 

 ing is formed and repaired, when we have taken a flight view of our 

 naked rocks, to difcover if they be really mouldering away, as thefe 

 gentlemen fuppofe. 



Mr. Kirwan confiders the rocks on the fea-fliore, expofed to the 

 breach of the fea, and almoft conftantly wet, as not fuffering the 

 flighteft diminution. I have examined many parts of our rocky coaft 

 with an eye to this queflion, and am clear that Mr. Kirwan is right : 

 I find no difference between the fpots where the fea breaks with the 

 greateft violence, and thofe which by fome local proteftion are left tran- 

 quil ; not the leaft appearance of wearing away is to be obferved at 

 either of them. 



The degradation of the dry inland rocks is more queftionable ; their . 

 furface is often well protefted by a covering of Lichen and Byffiis Saxa- 

 ii/is. The Trappe, I find, on our high grounds and mountains, are for 

 half an inch within the furface, fomewhat lefs found, and vary a little 

 in colour from the interior of the ftone; but I do not find, nor believe, 

 that they decompofc further, fo as to crumble down ; but if they do, the 

 materials only fall to the foot of the rock, where (at leaft in our moift 

 climate) they are foon covered with verdure, and arrefted for ever. 



Mr. Play/air fpeaks very pofitively on this fubjeft. He fays, "The 

 " atmofphere is the region where flones are decompofed, and again 

 " refolved into earth. This decompofition of all mineral fubflances ex- 

 ♦■' pofed to the air, is continual." [Illus. page 97.] 



" The law of decay is one that fuffers no exception." [Page 11 6. J 



I can by no means accede to thefe pofitions to the extent Mr. Plaf- 

 fair would carry them ; the calcareous rocks, it is true, that bound the- 

 valley of the Nile, are, as we are told by Denon, perpetually decompofing ; 

 but, on our northern fhore of Antrim, the atmofphere does not appear 

 to make the leaft impreffion on our immenfe facades of white limc'- 

 Ilone; and in Egypt, the granite has withftood decompofition above 

 4000 years. " The marks (fays Denon) of thefe firft operations, are pre- 



" ferved 



