406 Geological Society. 



and exhibits the following descending order: (1.) Calcareous shales, 

 forming the base of and passing into, the limestone ; (2.) Indurated 

 shales, alternating with sandstone and flagstone, occasionally of a 

 reddish colour; (3.) Sandstone, flagstone, arenaceous slate, quartz- 

 ite, &c., gradually passing into a slate formation. The authors re- 

 fer to various lists of fossils, and conclude that, though several spe- 

 cies are in common with those of the overlying Devonian system, 

 yet that as a group they are distinct : 1st. Because the carboniferous 

 species disappear ; 2ndly. Because some of the most characteristic 

 species of the lower limestone (such as the Stnjgocephalus Burtini, 

 &c.) are wanting ; Srdly. Because new (and Silurian) types begin 

 to abound ; more especially shales of the genus Ptennea, several 

 species of Orthis,theHomalonotusKnightii, Calymene JBlumenb(xchiii 

 &c. They further remark, that the species of Silurian fossils which 

 appear in the Eifel lists are mostly derived from the lower shales, 

 which are regarded as beds of passage. Along with known Silu- 

 rian fossils there occur also (as remarked in deposits under the 

 Westphalian limestone. Part I.) many other fossils, Delthyris mi- 

 croptera and D. macroptera, &c., in great abundance. The lower 

 quartzo-schistose rocks of Professor Dumont are therefore placed 

 in the Silurian system, but without any attempt to subdivide it into 

 distinct portions analogous to those of England. And as there is 

 no well-defined separation between this system and the overlying 

 Devonian, still less is there any well-defined separation between its 

 lower limits and the central slate rocks of the Ardennes. 



The slate country of the Ardennes is subdivided into three groups 

 of slate rocks, — Upper, Middle, and Lower. All the fossils ob- 

 tained by the authors from the upper group are of Silurian types. 

 Fi'om the middle and lower groups they obtained no fossils : but as 

 all the groups are linked together, and the upper is placed by its 

 fossils in the lower part of the Silurian system, they assign the two 

 lower groups to the upper Cambrian system. They then enter on 

 some mineralogical details connected with the structure of the slates 

 of the Ardennes ; and among the crystalline beds of the lowest 

 group (which they regard as only an altered portion of that which 

 is next superior), point out some examples of slates derived from a 

 cleavage transverse to the beds, and intersected by a true second 

 cleavage plane, a rare phaenomenon among the slates of England ; 

 but noticed by the authors among some rocks on the south coast of 

 Devon and the north coast of Cornwall. 



§ 2. Formations between the Eifel and the Hundsnick. — Left bank 

 of the Rhine, ^c. — Crossing the strike of the beds from the Eifel to 

 the Moselle, by several distinct traverses, the authors met with the 

 same series of deposits in descending order: viz. 1st. Calcareous 

 shales ; 2nd. Arenaceous flagstones and shale ; the upper part fre- 

 quently exhibiting a reddish tinge, and with portions more or less 

 calcareous, and the lower part passing into a great formation of 

 arenaceous flagstone, indurated slate and coarse slate, and occiision- 

 ally of fine quai'tzite. The series is here and there highly fossili- 

 ferous, containing several species of Pterinaea, Delthyris, Orthis, &c., 



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