ON THE GBOLOOICAL STRUCTURE AND AGE OF THE STRATA 

 OF SOUTH CORNWALL, 



Bx ALEXANDER SOMERVAIL. 



In a Paper published in the Journal for August, 1881, Mr. 

 Collins has entered into considerable detail regarding the 

 Greological Structure and Age of the Strata of South Cornwall ; 

 he differs very widely from the conclusions of De la Beche, 

 who surveyed the county and published his report thereon in 

 1839, in which he described the entire strata of this portion of 

 Cornwall as belonging to the Grauwacke group, or that group 

 of strata which underlies the coal, or whatever else that term 

 may include. 



Mr. Collins also differs very widely from the results laid 

 down on the most recently published maps of the Greological 

 Survey, which represent the whole area as of Devonian age, 

 with the exception of a small strip of strata on the coast at 

 Veryan Bay, coloured as Lower Silurian, mainly due to the 

 researches of Mr. C. W. Peach, and subsequently corroborated 

 by Murchison and Sedgwick, who visited the various localities, 

 and from fossil evidence, were able to refer the beds in question 

 to the Caradoc division, a member of the Lower Silurian 

 formation. 



The anomalous position of these Caradoc beds, overlying 

 the Devonian, was explained by Sedgwick as being due to an 

 inversion of the strata, and this explanation of a seeming 

 reversal in the order of succession appears to have sufficed up 

 to the present time. 



Subsequent to the researches of De la Eeche, Peach, 

 Murchison, and Sedgwick, much good work has doubtless been 

 done, and the results published in various Journals and Transac- 

 tions, especially in the Transactions of theEoyal Geological Society 

 of Cornwall, but I am not aware that the views entertained by 

 the above workers and the results published in the most recent 

 issues of the Geological Survey Maps have been much modified, 



