332 Sir R. I. Murchison on the Silurian Roch of Cornwall. 



the strong resemblance between the Mounts St. Michael in the 

 two countries ; and no one can have traversed these two regions, 

 without perceiving that, just as they evidently belong to the 

 same mineral type, so are their respective inhabitants descended 

 from a common stock, whose names of places have passed down 

 to their French and English descendants. The existence of 

 Caradoc sandstones and other Silurian rocks in that part of 

 France having been already indicated (Devonian and carboni- 

 ferous strata being also abundantly developed), their discovery 

 in Cornwall is a happy addition to that union of geological and 

 historical records, by which these widely-separated residences of 

 the Celtic race are illustrated. 



With regard to the highly mineralized or metamorphosed 

 conditions of great portions of the killas and sandstone of Corn- 

 wall, I can do little more than refer you to the few observations 

 I made at your anniversary meeting, and of which a brief abstract 

 has appeared in your newspapers. There are, as you well said 

 in your anniversary discourse, many analogies between the me- 

 tamorphic rocks of Cornwall on the one hand and those of Scan- 

 dinavia and the Ural mountains on the other ; whilst the paral- 

 lel is now drawn closer by the recent discovery of the Cornish 

 Silurian rocks. Your last erupted granites, elvans, and porphy- 

 ries, have played exactly the same part in traversing your Palseo- 

 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 quite 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 your 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 



* See Russia in Europe and Ural Mountains ; and Journal of the Geol. 

 Soc, No. 8. 



