62 The Rev. D.Williams on theGeology of Devon S^- Cornivall, 



to the other, we have nothing more than one great wave (of 

 probably some far extended undulation) consisting simply of 

 two convex arcs inclosing a central trough, apparently the 

 result of the same system of forces acting on a vast floor of 

 matter, successively and regularly accumulated; either an 

 overlying mass, or a fractured section of an original continua- 

 tion of the Cambrian and Silurian deposits; for if we compare 

 the precipitous and vertical cliffs of Nos. 2, 3, 4 and 5, of 

 Exraoor (in echellon arrangement beetling over the deep tide 

 way of the Bristol Channel) with the carboniferous limestone 

 and secondary rocks of the opposite coast of Wales, we have 

 all the evidences of an enormous fault. 



But what are the results if we compare the positive testi- 

 mony afforded by gradation, alternation, succession, and con- 

 formable supi-aposition, with that afforded by organic re- 

 mains? The Pethervvin fossils near Launceston, and those 

 of the coral limestones of South Devon, I include without 

 doubt or hesitation in a lower horizon, or subdivision of the 

 floriferous series, No. 9, above the Posidonia limestones ; so 

 that if we suppose the ratio of extinction of vegetable species 

 not to have been governed by the causes which effected that 

 of marine zoophyta and testacea, the exceptions afforded by 

 the Posidonia limestones are but as dust in the balance of or- 

 ganic evidence; and in this respect alone, geologists will in- 

 volve themselves in inextricable difficulties and contradictions, 

 if they reject the maximum and rely on the minimum amount 

 of organic evidence. I repeat the fact, that the lower flori- 

 ferous, and Coddon Hill grit series are overlaid in the south 

 by the slates of Cornwall, which comprise in their ascending 

 terms, first, the St. Germans, and lastly, the Plymouth lime- 

 stones ; so that it appears to me, that the great consecutive 

 series from No. 2 to 10, evidences a transition of organic type, 

 in progress, as it were, from the grauwacke towards the car- 

 boniferous limestone; that the latter, or its coal-field, is not ' 

 represented here at all, but that the coarse slaty and red 

 arenaceous beds which overlie the Plymouth limestones, ex- 

 tending thence to Rame Head on the south, probably do ap- 

 pertain to the early period of the Old Red Sandstone pro- 

 per. 



The relations of the floriferous. No. 9, to the coral lime- 

 stones, and kiilas. No. 10, are explained with the greatest 

 clearness and simplicity at and around Chudleigh ; to aid my 

 brief description 1 refer your readers to the accurate and 

 faithful sections of Mr. De la Beche. (See Report, Plate IV. 

 fig. 7 and 8). But why that able observer should assign a 

 different position to the many other groups of coral limestone 



