Geological Society. 425 



The authors next institute a comparison of the formations of 

 Westphalia and Nassau with those of Liege, the Ardennes, and 

 Eifel on the left bank of the Rhine. Starting from the country 

 around Liege, which M. Dumont has rendered classic bj' his illus- 

 trations and his map, Messrs. Sedgwick and Murchison confinn the 

 views of that author, and bear testimonj' to the great value of the 

 method employed by him in bringing into symmetrical condition 

 that highly tortuous and convulsed tract. They admit that he has 

 most successfully demonstrated the replicatures of the diffei'ent 

 members of the Carboniferous and infra-carboniferous systems, and 

 established on clear physical evidence, the fact that whole basins 

 liave been inverted. They differ from him, however, in the compa- 

 rison he has made between the older rocks of his own countiy and 

 those types of classification which the authors have established in 

 the British Isles. In his table of comparison, M. Dumont supposes 

 that the Old red sandstone of England has no equivalent in Belgium, 

 and that the formations which thei'e occur beneath the Carbonife- 

 rous limestone (his terrain anthraxifere^ are the equivalents of the 

 Silurian system ; our authors show that the psammites, schists, and 

 limestones next below the coal-field and cai-boniferous limestone of 

 Liege are the exact equivalents of the series which in Westphalia 

 represent tlie Devonian system. The fossils are the same as those 

 of Elberfeldt, Paff'rath, and Devonshire. These beds also contain 

 fishes of the genus Holoptijcliius, which Agassiz has identified with 

 types of the old red sandstone; and on all these grounds, as well as 

 by complete lithological and stratigraphical passage into the over- 

 lying carboniferous group, our authors establish that the terrain 

 anthraxifere of D'Omalius and Dumont is, like the schistose rocks 

 of Devonshire, the true equivalent of the old red sandstone. 



The mountains of the Ardennes consist in their upper members of 

 equivalents of the Silurian system, as indicated both by order of in- 

 fraposition to the Devonian rocks, and by containing the same types 

 of fossils which characterize the Silurian strata on the right bank of 

 the Rhine ; whilst the oldest slaty rocks, in which no fossils have 

 been discovered, are presumed to be in the parallel of the Upper 

 Cambrian group. 



Tiie limestones of the Eifel, well known by their fossils, lie in 

 a basin supported by Silurian rocks, and are identical M'itli the 

 lower Devonian limestones of Liege, Westphalia, and Nassau; whilst 

 the shales beiu;ath them graduate into Silurian grauwacke, and con- 

 tain so many Silurian species tiiat (together with the well-known 

 sciiistsof Wisscnbacii on the right bank of the Rhine) they are con- 

 sidered to form the uppermost members of the Silurian division. 



A similar succession to that from the Eifel to the Ardennes is 



Devonshire, with the very peculiar trilobite, Brontes flahellifer of Goldfuss. 

 'ITie upper members of the Silurian system arc distinguished by Orthocc- 

 ratites, Ilomalonoti, and other Trilol)ites, Pterinotc, Orthis, &c., some of 

 which arc identical with species found iu the Silurian region ; with these 

 arc some remarkable forms not yet detected in the British Isles, such as 

 Delthyris macroplcra and D. micruplcra. 



