JURASSIC OF THE PARIS BASIN. 



501 



other by intervals in which older or newer rocks occupy the surface 

 of the ground. These are 



I. From the Ardennes to the Cher. 

 II. The two Charentes. 



III. Normandy, with Orne and Sarthe. 



IV. The Pays de Bray. 

 Y. The Boulonnais. 



The first-named district, though not the nearest to England, nor 

 presenting characters most similar to those of our own country, yet, 

 from its large size, the continuousness of its deposits and the labour 

 that has been bestowed upon them, presents itself as the most typi- 

 cal for France, and the one therefore to be studied first, so that we 

 may better understand the last three, which in some sense are in- 

 termediate between the French and English types. 



I. From the Ardennes to the Cher. 



Although this range has been studied continuously from one end 

 to the other, it is necessary in description to subdivide it into those 

 smaller areas which have been made the subjects of special mono- 

 graphs by French geologists. 



1. The Ardennes Department. — The rocks of this area have received 

 illustration at the hands of MM. Sauvage and Buvignier (2) *, who 

 give the following classification 



1. Upper Group. 



a. Marls with Exogyra virgula, 160 ft. 



b. Calcaire a Astartes, 21 ft. 



2. Coral Rag, 250 ft. 



3. Oxpordian. 



a. Ferruginous oolite, 28 ft. 



b. Marls and limestones, 300 ft. 



(l) Shelly siliceous limestone, (2) marls, (3) ironstone. 



c. Lower marls with ironstone, 30 ft. 



Commencing this series from the base, 3 c may be passed over as 

 Callovian, while 3 b (2) and (3), forming the great mass of the 300 ft. 

 and occupying the valleys, will represent the undoubted Oxford Clay. 

 The series 3 b (1) then commences the group of rocks now under 

 study. If for "siliceous limestone" we read its equivalent, " calca- 

 reous grit," we have the term which will exactly suit the English 

 geologist, who at once recognizes in it a representative of his ' Lower 

 Calcareous Grit.' At the base, as seen in quarries on the road from 

 the station of Launois to Neuvizy, is hard blue calc-grit ; and above 

 this, nodular beds of grit in a subargillaceous matrix. Some of 

 these are very light, like the Upper Calcareous Grit of Yorkshire, and 

 are said by Sauvage and Buvignier to be soluble in potash, indicating 

 a possible organic origin, like the Renulina-grits of Scarborough ; 

 the fossils, however, are in some cases ' beekized.' These nodular 

 beds, which begin to present some of that peculiar feature indicated 



* See list of works above. 



