404 Geological Society. 



in England, e, ^9. Hysterolites of Schlotlieim, and two species of Del- 

 thyiis, — D. macroptera and D. microptera (Goldfuss). The same 

 groups of fossils are found on the banks of the Rhine ; and in a 

 quarry near Unkel are many fossils of the genus Orthis, among 

 which were O. pecten, O.flahellula, 0. ruffosa. Along with them 

 was Terebratula Stricklandii, and the group was considered charac- 

 teristic of the lower Silurian rocks of England. 



On a review of the whole evidence, the authors place this vast 

 succession of strata in the Silurian system, without professing to 

 separate the several parts into distinct groups, on a parallel with the 

 several groups of the Silurian system of England. This is forbid- 

 den by the absence of distinct calcareous bands, and also by the 

 great vertical range of some of the fossil species, which are found 

 almost from the highest beds to the lowest of the whole series. 

 Several lists of fossils are then given, in confirmation of these gene- 

 ral views ; and it is thence concluded, that the great sequence of 

 coarse earthy schists, calcareous bands, arenaceous flagstones, psam- 

 mites, &c., are the representatives of the ujjper Silurian system, and 

 that the lowest quartzose, graywacke, flagstone, roofing-slate, &c., 

 which in some places have no fossils, and in others have numerous 

 repetitions of a few species of the genus Orthis, belong to the lower 

 Silurian, or upper part of the Cambrian Systems. 



Part II. Older formtdions on the left bank of tlie Rhine. — The 

 Hartz. — Upper Franconia, Sfc. 



§ 1. The authors commence with a short description of the phy- 

 sical region extending from the coal-field of Belgium to the south- 

 eastern flank of the Ardennes, and then in like manner describe the 

 country between the same coal-field and the limestone of tlie Eifel. 

 They afterwards discuss, at some length, the methods used by Pro- 

 fessor Duraont to determine the superposition of the natural groups; 

 and partly from considerations derived from the symmetrical ar- 

 rangement of the mineral masses, and partly from the direct evi- 

 dence of sections, especially in the Eifel country, show that the 

 geological sequence has been correctly determined. So far adopt- 

 ing the views of Professor Dumont, the descending order in the 

 provinces above-mentioned is as follows : — 



(1.) Coal country Terrain Houillier. 



(2.) Anthraxiferous country. Terrain Anthraxifere. 



(3.) Slate country Terrain Ardoisier. 



The second of these divisions is subdivided into four natural 

 groups or systems, viz. Upper calcareous sj'stem ; Upper quartzo- 

 schistose system ; Lower calcareous system ; Lower quartzose-schi- 

 stose system. 



The slate country is also divided into three groups, — Upper, 

 Middle, and Lower. 



The order being assumed as fixed, the next question is as to the 

 British equivalents of the successive divisions or subordinate sy- 

 stems. 



Respecting the Belgian coal-field, there is no doubt : it is on the 

 same horizon with the great coal-fields of England. Through a 



