246 Prof. Sedgwick and Mr. Murchison 07i the Classification 



part of the limestones and slates of South Devon : and lastly, 

 he found near South Petherwin what appeared an unequivocal 

 passage between the fossiliferous slates and the overlying culm 

 series. From these facts it follows; 1st, that the fossiliferous 

 slates of Barnstaple, on the north side of the great culm 

 trough, must be nearly of the same age as those of South 

 Petherwin on its southern side; for certainly the inferior 

 strata of the culm series are the same, or very nearly the 

 same, at the two localities ; 2nd, either that the culm series 

 was older, or the fossiliferous slate of North Cornwall newer 

 than we had supposed in our memoir of June 1837. Under 

 . these circumstances, it became doubly important to examine 

 large suites of fossils, before we could arrive at a correct con- 

 clusion as to the true place of the older Devonian strata in 

 the geological series*. 



The n)ost extensive collection of fossils which had been 

 made in South Devon, were from the Plymouth limestone bj' 

 the Rev. R. Hennah, and from the limestones of the neigh- 

 bourhood of Newton Bushell by Mr. Austen. The latter 

 was sent to the Geological Society to illustrate a memoir by 

 that gentleman; and the inspection of its contents convinced 

 Mr. Lonsdale, that i&v/, il' any, of the organic remains could 

 be strictly identified with species of the carboniferous limestone 

 to which Mr. Austen compared them ; for although there 

 were some which had a close resemblance, still there wei'e 

 many which bore the impress of a distinct type, while others, 

 particularly the corals, seemed to approach to certain forms 

 of the upper Silurian group; and hence Mr. Lonsdale was 



* The fossils of South Petherwin, from the first, presented a great diffi- 

 culty. One or two of them very nearly resembled mountain lime fossils; 

 and as a group they were not identical with any series we had before ex- 

 amined. This induced one of the authors to join Mr. Austen (in Jul)', 

 1837) in an excursion to that neighbourhood ; thinking it possible that the 

 South Petherwin limestone might form a part of the base of the culm- 

 measures. An unseasonable interruption compelled them, after two or 

 three days, to leave the country : but they ascertained, 1st, that the lime- 

 stone in question did not form a part of the culm series; and 2nd, that the 

 fossils of South Petherwin, &c., were, as a group, nearly the same with the 

 fossils of South Devon ; thus confirming a previous conclusion (drawn 

 from less perfect evidence), that the fossiliferous systems of South Devon 

 and of Cornwall were the same. They also found one junction (since 

 visited and sketched by Mr. De la Beche, Report, &c. p. 107.) in which the 

 culm beds appeared to rest unconformably on the older slates. This kind 

 of junction seems to form the exception and not the rule ; and does not, 

 we think, invalidate the statement made above. Many such junctions might 

 indeed be found in the very heart of the culm-measures, where the beds 

 are all of one age. Such an appearance of want of conformity does not 

 therefore invalidate the fact of a true passage from the Petherwin slates 

 into the culm-measures. 



