690 Professor Sedgwick and R. I. Murchison, Esq ., on the 



of the old red sandstone. We were aware, indeed, that several of the South 

 Devon fossils conformed nearly, perhaps specifically, to the type of the carbon- 

 iferous limestone. But on the other hand, no one was able to define the de- 

 scending range of such organic forms; especially as it was asserted, that they 

 reappeared in the south of Ireland, in beds alternating with true greywacke — 

 or rocks supposed to be older than the old red sandstone. Hence we placed, 

 provisionally , but with no satisfaction to ourselves, or confidence in our evi- 

 dence, all the older fossil groups of Devon and Cornwall in that great but ill- 

 defined interval that exists between the Caradoc sandstone and the older 

 slates of North Wales. Since 1836 we have received repealed proofs of the 

 insecurity of our first hypothesis. Thus, Mr. De la Beche (1837) exhibited 

 fossil plants from the quarries of Marwood (PI. LI., sec. 2.) one of which 

 Professor Lindley identified with Sligmaria ficoides, a very common coal- 

 plant ; and near the same place we had ourselves found a Belleropkon, not to 

 be distinguished from B. lobatus of the old red sandstone. Again, Mr. 

 Lonsdale, after an extensive examination of the fossils of South Devon, had 

 pronounced them, more than a year since, to form a group intermediate be- 

 tween those of the Carboniferous and Silurian systems, and hence he con- 

 cluded that the fossiliferous rocks of South Devon were subordinate to the 

 old red sandstone. This view could be effectually maintained only by one 

 who knew the fossils of the Silurian system. The work in which those fossils 

 are described, proves that the fossils of the Silurian and carboniferous systems 

 are quite distinct. It also proves that the fossils of the old red sandstone of 

 Herefordshire are of a peculiar type ; and, at the same time, it points out a want 

 of zoological continuity in the development of organic forms between the 

 epochs of the carboniferous and Silurian deposits. There is, indeed, a true 

 zoological transition between the highest group of the Silurian system and 

 the lower part of the old red sandstone ; but between the middle and upper 

 groups of the old red sandstone and any part of the carboniferous limestone 

 no such transition had been discovered. These facts were well known to Mr. 

 Lonsdale, and hence his conclusion respecting the age of the South Devon 

 limestone was based on incomparably better evidence than the mere specific 

 resemblance of some of its fossils to those of the carboniferous limestone: 

 for he contended, as above stated, that the organic remains of South Devon 

 formed a connecting link between the carboniferous and Silurian fossils ; and 

 thus supplied that zoological continuity which before had been sought for, 

 but never found. 



But this is not the whole of the evidence by which we were gradually led 



