226 Professor Sedgwick and Mr. Murchison on the 



in its structure and its fossils the perfect counterpart of the great limestone of 

 South Devon. 



We also assumed on the authority of the best geologists who had recently 

 visited the country, that the Eifel limestone was the exact equivalent of the 

 Wenlock limestone of the Silurian system. Hence we were led also to con- 

 clude, before we exammed this deposit, that it must form a saddle, rising from 

 under rocks which we had regarded as Devonian or upper Silurian. The ex- 

 treme perplexity of the Rhenish sections, and the, entire reversal of the forma- 

 tions in the neighbourhood of Miinster Eifel (where we first saw the hmestone) 

 confirmed us in this error*. But we soon afterwards found that the Eifel 

 limestone formed an undoubted trough reposing on the system of beds before 

 alluded to — that it was very nearly the equivalent of the lower limestone of 

 the systeme anthraxifere of Professor Dumont — and that it was in like man- 

 ner the equivalent of the lower of the two Westphalian limestones above men- 

 tioned. 



The great importance of determining the true age of the Eifel limestone was 

 therefore evident. For if it were the exact equivalent of the Wenlock limestone, 

 then would there be an end of the greater part of the Devonian system ; which, 

 during our labours in the earlier part of the summer, we thought we had so firmly 

 established on the right bank of the Rhine, in the Hartz, and in Upper Franconia. 

 We were, however, staggered, not merely by all the authorities which seemed 

 combined against our first views ; but, we may also add, by the many undoubted 

 Silurian fossils, especially corals, which are found in the Eifel limestone ; so that 

 we returned to England in considerable uncertainty as to the exact result of our 

 summer's labours. We had, however, established certain base-lines to which we 

 could refer our numerous and laborious sections ; and for their further illustration 

 we had a large coordinate series of fossils ; and out of such elements it was hardly 

 possible to fail in establishing a true sequence of geological groups, whatever might 

 be their classification when put in comparison with the older formations of this, or 

 any other distant country. 



Without anticipating, unnecessarily, the details of this communication, we may 



state, that an examination of our fossil evidence has now led to a satisfactory 



conclusion, viz. that there is a group of rocks, characterized by an appropriate 



group of fossils, in a position, geologically as well as zoologically, intermediate 



between the carboniferous and Silurian systems. The supposed " Ludlow Rock " 



of Belgium passes into the mountain limestone, and even in its lower portions 



does not, as far as we know, contain a single Silurian fossil : and our Eifel mol- 



* It was while we were labouring under this error that one of the authors examined the inferior strata 

 of the Boulognais. See ' Bull, de la Soc. Geol. de France,' vol. x. p. 404 et seq. 



