404 Tl'pfield Green — The Cornish Beds and the Gedinnian. 



through Fowey and Looe along the coast, and across the Start 

 peninsula as far as Babbacombe, south of Dartmouth in Devonshire. 

 They are referred to by Ussher ' as 'Dartmouth Slates.' They exist 

 also on the north of the Devonian basin, and are mentioned by 

 Etheridge'^ as underlying the Lower Devonian. 



Reference has of course been made to them by various English 

 authors, but few have attempted to assign to them a definite 

 stratigraphical position, and fewer still have studied them in detail 

 or made any investigation of the Continental equivalents occupying 

 a similar position in the Devonian series. 



Literature. 



The earliest reference I can find is by Berger^ in 1811, the next? 

 by Sedgwick^ in 1821-2, who was followed by Conybeare* in 1823. 

 In 1832 Boase*^ published an exhaustive petrological description of 

 the district (according to the light of that time), founded on no 

 less than 1,085 specimens deposited in the Museum of the Royal 

 Geological Society of Cornwall, with a series of sections. He also 

 attempted an extension of the hitherto accepted nomenclature of 

 the components of the rocks (pp. 369-425 of his paper), which he 

 termed 'Ocrynian.' 



In 1838-40 Sedgwick and Murchison,' De la Beche,^ and the 

 Rev. D. Williams ' made the first serious attempts at unravelling the 

 structure of the county, while T. Weaver^" commenced a comparison 

 with Continental areas. Since then no comprehensive description 

 has appeared, but isolated papers may be found in the Proc. Roy. 

 Geol. Soc. Cornwall, Roy. Inst. Cornwall, and the Quart. Journ. 

 Geol. Soc. London, by J. H. Collins, 1872-1903, Howard Fox, 

 1885-1903, and others. 



Collins " considered the whole of the beds at the extreme south- 

 west of the countj% from Penhale to Breage, as pre-Silurian ; a small 

 strip, extending from Penhale to the Van and St. Austell, and the 

 area south of Porthmellin and Gwennap to Mullion and Porthalla, 

 as Lower Silurian; Newquay and Ladock and a small extent of 

 ground on the coast to the north of Porthalla as 'Ladock beds' = 

 Upper Silurian. For a comparison of the northern exposures in 

 Devonshire with other areas, Sharp, Quart. Journ. Geol. Soc. ix 

 (1853) ; Jukes, Quart. Journ. Geol. Soc, xxii (1866), and Additional 



1 Summary Progress Geol. Survey, 1902, pp. 160-165. 

 - Quart. Journ. Geol. Soc, xxiii (1867), p. 585. 

 3 Trans. Geol. Soc, i, p. 93. 



* Trans. Cambridge Phil. Soc, i, pp. 89, 291. 



* Annals Phil., ser. ir, v, p. 184, and vi, p. 35. 

 « Trans. Geo!. Soc. Cornwall, iv, pp. 234-264. 

 ' Trans. Geol. Soc, ser. ii, v, p. 633. 



** Geol. Survey. 



" Proc. Geol. Soc, iii, pp. 115 and 158 ; and Phil. Mag., ser. in, xvi, pp. 59-64. 

 10 Phil. Mag., ser. in, xvi, pp. 59-64. 



" Journ. Eov. Inst. Cornwall, vii (1881), p. 37, and Trails. Eoy. Geol. Soc 

 Cornwall, x (2), 1880, p. 51. 



