272 Professor Sedgwick and Mr. Murchison on the 



or dirty greyish-green, earthy schist or mudstone, extremely resembling many of the most characteristic 

 varieties of Ludlow rock*. Its whole thickness must be very great, though difficult to compute cor- 

 rectly from the number of undulations. Through the intervention of beds of hard grey sandstone it 

 passes, in some places, into the upper division of yellow psammite (above described) : and near the 

 same part of the series are sometimes seen calcareous bands with numerous organic remains, especially 

 Terebratulae and Spirifers. Still lower in this division (for example, on the road from Liege to Spa, 

 and on the road from Liege to Marche-en-Famenne) are found calcareous bands, and beds of calcareous 

 shale, sometimes of a reddish colour, with many calcareous concretions, and associated with these are 

 numerous organic remains. The species are enumerated in the accompanying lists. But we may ob- 

 serve, by the way, that neither in the yellow psammites of the upper division, nor on any part of the 

 calcareous and fossiliferous earthy schists of the lower, did we find a single Upper Silurian fossil. Coupling 

 this fact with the passage of the upper part of the formation into the mountain limestone, we reject any 

 inference which may be drawn from a mere mineral resemblance of the lower beds to certain portions of 

 the Ludlow rock ; especially when we consider how inconstant are these mineral characters in our own 

 country, and how utterly unlike the upper Silurian rocks of Westmorland are to those of Shropshire, 

 Herefordshire, &c. 



3. Having thus, we think, proved that the second member of tlie terrain anthraxifere of Prof. Dumont 

 is clearly not the equivalent of the Ludlow rock of the British Silurian system, we now proceed to notite 

 the two inferior divisions, which are considered by him as the equivalents of the Wenlock limestone and 

 Caradoc sandstone. The lower litnesione of Belgium rises immediately from beneath the formation last 

 described, without any break of continuity or any appearance of interrupted sequence. It is a formation 

 well defined in character and of great thickness. It is distinguished from the mountain limestone by its 

 position, and partly also by its structure ; for it is, on the whole, closer grained, and has often a kind of 

 scaly fracture, resembling, in that respect, certain varieties of South Devon limestone. It sometimes 

 also puts on a kind of slaty structure, often seen in old limestones alternating with schistose rocks, but 

 very seldom found in true mountain limestone. It is also entirely distinguished from that limestone by 

 its corals (Favosites polymorpha, Stromatopora concentrica, &c.) ; in which respect it is identical with 

 the South Devon limestone, and also with the great lower limestone of Westphalia, described in the 

 former part of this paper. Its colours are however very variable ; and it has dark carbonaceous beds 

 (hence its name anthraxifere) which burn to a white lime, and are not distinguishable from common 

 varieties of carboniferous limestone : and moreover it has, in a few places, like that limestone, thin- 

 bedded and close-grained masses of a dark colour and conchoidal fracture, which are polished for black 

 marble. Such is the position, and such are the prevailing characters of the lower Belgian limestone. 

 Its fossils are given by M. Dumont, and have been discussed by Mr. Lonsdale ; and appeared to us un- 

 equivocally the same (considered as a group) with those of the great lower Westphalian limestone (of El- 

 berfeldt, Iserlohn, &o.). Hence all the arguments by which we endeavoured to prove the age of the 

 latter, may here be applied to determine the epoch of the former. In short, it is in position on the sec- 

 tions, in its structure, in its great extent, and in its group of fossils, a true Devonian limestone : and we 

 shall further recur to this subject, after we have, in the progress of this paper, noticed the Eifel limestone. 



4. We must in the next place shortly notice the lowest formation of the anthraxiferous system of M. Du- 

 mont. It is essentially composed of psammites and schists. The psammites pass into beds of hard, siliceous 

 flagstone and strong beds of gritstone ; and in some places (chiefly in the upper portions of the formation) 

 into beds of coarse conglomerate, which are sometimes of a grey, and sometimes of a brownish red 



* It was the lithological resemblance of these beds to the Ludlow rock which induced M. D'Onialius 

 D'Halloy and M. Dumont to identify them with that deposit. 



