Sir R. I. Murchison on the Silurian Rocks of Cornwall. 343 



zoic sediments, as like rocks have done in Norway. Cornwall 

 may also be compared to large portions of Siberia, and notably 

 to the Ural mountains, whose chief eruptions have taken place 

 through deposits of Silurian, Devonian, and carboniferous age. 

 In both countries the eruptive rocks are granites, porphyries, 

 greenstones and serpentines : even in their superficial accumula- 

 tions there is this striking resemblance, that the Cornish detritus 

 and gravel (as clearly pointed out by Mr. Carne) is purely local, — 

 the county being cjuite as exempt from all far-transported mate- 

 rials as the Ural mountains and Siberia. With this absence of 

 all foreign transport or drift, Cornwall is as instructive as the 

 Ural in never exhibiting those " roches moutonnees " and those 

 polished and striated surfaces which have (in my opinion) been 

 so erroneously referred to the action of land glaciers, in all those 

 low regions of the earth, where they have clearly been caused by 

 the action of powerful aqueous drift, in the manner I have else- 

 where attempted to explain ^\ - 



Your stanniferous gravel bears, indeed, precisely the same re- 

 lations to yom- granite and killas, as the auriferous deposits of 

 the Ural to the eruptive and schistose rocks of that chain. Both 

 are mere local, shingle accumulations, derived from veinstones 

 which have been denuded from the surface of adjacent crystalline 

 rocks. With these analogies there is however a marked distinc- 

 tion between Siberia and Cornwall. All richly auriferous chains 

 (Humboldt first remarked the fact) have a meridian direction, as 

 in the Ural, and various north and south parallel ridges in Si- 

 beria and other parts of the globe. The axis of Cornwall, on the 

 contrary, is transverse to that direction, viz. from E.N.E. to 

 W.S.W. ; and though containing copper ore in common with 

 the Russian mountains, it differs from them in not producing 

 gold or platinum ; whilst it is peculiarly distinguished by con- 

 taining tin, which is unknown in the Ural. Let us hope that 

 the day is fast af)proachiug, when the cause of the production of 

 such striking phieuomena as these will receive some explanation 

 at the hands of those physical philosophers, who are advancing 

 a line of research in which your own countryman Mr. R. W. Fox 

 has already so distinguished himself. But if gold does not exist 

 (in any aj)])reciablc quantity at least) in your otherwise richly 

 endowed mineral county, there are, 1 am happy to say, good 

 grounds for hojie, that in their most distant great colony English- 

 men may find it abundantly. In an address to the Royal Geo- 

 graphical Society, delivered in INIay 1845, when conuncnting 

 upon the valualjle labours of Count Strzelecki in decijjhering the 

 structure of th(! great north and south cliain which ranges along 



• See Russia in Europe and Ural Mountains; and Journal of" the (icol. 

 Soc, No. 8. 



