276 M. BttONGNiAiiT on the Calcareo-trappem 



other, the author names the conglomerate, trappean brecciola 

 (brecciole trappeenne). This brecciola, which is not a 

 basalt, nor even a compact lava, alternates with a limestone 

 containing nummulites and some fossil shells, the analogy of 

 •which to those of the calcaire grossier of Paris is remarked 

 by M. Brongniart. Higher up, towards the commencement 

 of the valley, the basalt appears and seems to rise from the 

 midst even of the Brecciola. 



This formation of brecciola and upper sediment limestone, 

 commonly named tertiary limestone, appears to fill the bot- 

 tom of a great valley, formed, previously to this deposite, in 

 a compact and much more ancient limestone, occurring in 

 an oblique and unconformable stratification with the brecci- 

 ola formation. The author refers this limestone to the Jura 

 limestone ; as also a great part of that which occurs at the 

 foot of the Alps in the same geological situation. 



2. The Val Ronca, celebrated for the great abundance of 

 shells found there, in general presents the same structure ; 

 but the alternation is less regular, the brecciola is in a thicker 

 mass, and the basalt more abundant ; the yellowish lime- 

 stone, which even mineralogically resembles the calcaire 

 grossier of the environs of Paris, is filled with a multitude 

 of nummulites. These fossil shells, which have rendered 

 the place so celebrated, are scattered in the brecciola be- 

 neath the limestone beds. The author gives a very detailed 

 enumeration of these shells, with descriptions and very exact 

 figures of all those which he has not found described, or 

 which have not been so well figured as to be recognised. 

 The shells, to the number of more than eighty species, 

 principally described and figured from specimens and the 

 information of M. Manischini, of Schio, are all so similar, 

 even as to species, to those of the calcaire grossier of the 

 environs of Paris, that we may, in many cases, regard them 

 only as simple varieties; more than tweuty are even analo- 

 gous to the species found in the Paris basin, and the author 

 has then contented himself by mentioning them by the names 

 given them, either by M. de Lamarck, or other concholo- 

 gists. Among the analogous species are the following : 



