214 J. B. Hill — The Palceozoics of West Cornwall. 



Worlc of oilier observers in the district. 



The geological litei-ature of West Cornwall is so voluminous that 

 it would be impossible within the compass of this paper to do justice 

 to the work of previous observers. In 1821 the Nare Point con- 

 glomerate was referred to by Sedgwick, who noted its mechanical 

 origin and its passage into the ordinary grauwacke of the district.^ 

 It is evident from a perusal of De la Beche's Report, that had he 

 differentiated the Silurian strata from the Devonian, he would have 

 included among the former some of the killas in the Meneage 

 peninsula. As already remarked, Murchison expressed the opinion 

 in 1846 that much of the strata between Gerrans Bay and Falmouth 

 would prove to be of Silurian age. The killas of West Cornwall 

 has formed the subject of various papers by Mr. J. H. Collins, 

 whose researches, extending over many yeai's, prove the zeal and 

 enthusiasm with which he attacked this thorny problem. In 1881 

 Mr. Collins published a sketch-map with his paper on the Geology 

 of Central and West Cornwall,^ in which he not only divided the 

 killas into numerous units, but assigned them respectively to 

 the Devonian, Upper Silurian, Lower Silurian, and Cambrian 

 formations, that were separated from each other by unconformities. 

 Although Mr. Collins' general conclusions cannot be sustained, he 

 subsequently correlated the conglomeratic series of Meneage with 

 the Ladock Beds (the latter being, in part at least, equivalent to the 

 Grampouud and Probus grits), and assigned them to the Lower 

 Devonian.^ He recognized also that the killas of West Cornwall 

 was mainly of Lower Palasozoic age, and had he confined himself 

 to that broad generalization his paper would have ensured a more 

 lasting recognition. He also placed the Ponsanooth Beds, which 

 to some extent represent the Mylor Series, at the base of the 

 killas, which may probably be correct. Mr. A. Somervail * contro- 

 verted some of Mr. Collins' conclusions, but agreed with him as to 

 the Pre-Devonian age of a large part of the killas, and assigns 

 a Lower Silurian age to the slates from Gerrans Bay to the vicinity of 

 Penryn, most of which had been siniilaidy classified by Mr. Collins, 

 and Mr. Somervail suggested that they were of Llandeilo age. In 

 1891 Mr. Ussher published a sketch-map with his paper,* dealing 

 with the Devonian rocks as described by De la Beche and supple- 

 mented by his own researches on that formation. In that map 

 Mr. Ussher has likewise shown the western killas (now representing 

 the Mylor, Falmouth, and Portscatho Series) as (?) Pre-Devonian, 

 and has placed the Grampound grits at the base of the series classed 

 as undoubted Devonian. Mr. Upfield Green has claimed the beds 

 represented by the Mylor, Falmouth, and Portscatho Series as 

 Lower Devonian, of which the Dartmouth slates represent the 

 upper member, while the base is marked by the conglomerate 



* Trans. Cambridge Phil. Soc, vol. i. 



2 Journ. Eoy. Inst. Cornwall, vol. vii, p. 17. 



* Journ. Roy. Inst. Cornwall, vol. viii, p. 186. 



* Jouni. Roy. Inst. Cornwall, vol. ^ii, pp. 262-273. 

 5 Trans. Roy. Geol, Soc. Cornwall, 1891. 



