J. B. Hill— The Palceozoics of West Cornwall. 215 



of Meneage, etc.^ Mr. Green's conclusions were criticized by 

 Mr. Ussher, who contended that the superposition of the Dartmouth 

 slates to the Mylor, Falmouth, and Portscatho Series was not 

 supported by proofV'^ Mr. Ussher recalled that although he formerly 

 correlated the Grampound grits with the Gedinnien, he would 

 now hesitate to do so, the inference apparently being that they 

 might occupy a higher horizon. In that paper Mr. Green refers to 

 the Portscatho and associated series as consisting "chiefly of grits 

 varying much petrologically, but mostly felspathic," and correlates 

 them with arkose or felspathic grits that occur next- to the con- 

 glomerate on the Continent. As the conglomerate is now shown 

 to be unconformable to the Portscatho Beds, it is of little importance 

 to point out that the latter are more properly defined as siliceous 

 grits, in which felspathic constituents play only a subordinate part, 

 so that their correlation with the Continental arkose referred to 

 cannot he supported on petrological grounds. In 1894 Mr. Clement 

 Eeid pointed out that towards Gorran Haven " shore conglomerates, 

 belonging probably to upper part of Lower Devonian, rest directly 

 on Ordovician or still older rocks." ^ 



Finally, the researches of Mr. Howard Fox on the Eadiolarian 

 cherts of West Cornwall, and the assistance he has received in their 

 determination by Dr. Hinde, must be referred to. Mr. Fox has 

 shown that not only are these organisms confined to the horizon of 

 the pillow lavas, which indicates such a remarkable association with 

 Lower Silurian horizons in the south of Scotland and elsewhere, but 

 he has proved their existence throughout the Silurian sequence of 

 West Cornwall. The fact, moreover, that the most patient search 

 has failed to detect their presence in the Devonian strata has 

 furnished additional evidence in support of the differentiation of 

 those systems in this region. On the assumption that the Old Red 

 Sandstone was deposited in great inland basins it is possible that the 

 British Devonian rocks, being so closely adjacent to the Welsh lake 

 basin, were laid down in a partially enclosed sea like the Medi- 

 terranean, from which the oceanic organisms might have been almost 

 entirely excluded. 



Summary and Conclusion. 



The main conclusions may be epitomised as follows : — 



1. The Lower PalaBozoio divisions, including the Veryan, Port- 

 scatho, Falmouth, and Mylor groups, form a natural sequence. 



2. The Upper Palasozoio, represented by the Manaccan Series, rests 

 unconformably on the Lower Paljeozoics, and its constituents have 

 been largely derived from the Veryan and Portscatho groups. 



3. The Veryan and Portscatho groups were consolidated and 

 veined with quartz, prior to their denudation and incorporation 

 in the Manaccan conglomerate. 



1 Geol. Mag., 1904, p. 403. 



2 Geol. Mag., 1904, p. 590. 



* Surnmar}' of Progress of Geological Surrey for 1904, pp. 22-23. 



