242 



3IR. T. ROBERTS ON THE UPPER JURASSIC ROCKS 



The Callovian presents but a feeble development in this district, 

 as compared with that of the northern area. The fer sous-oxfor- 

 dien, which is so constant in the latter, is scarcely, if at all, repre- 

 sented in the southern district. Its total thickness does not exceed 

 16 feet, and it is usually considerably less. It is, however, pos- 

 sible to distinguish two zones in it : — 



2. An upper one, composed of grey clay, poor in fossils, and some- 

 times containing pyrites. 

 1. A lower limestone, which is ferruginous and rich in fossils. 



In the ' Combe Grede,' near St. Imier, a somewhat peculiar 

 development of the Callovian is seen : it consists of a bed of 

 greyish chert 8 inches thick. The underlying Dalle nacree, how- 

 ever, is very well developed here, and may, in part, represent the 

 Callovian of other areas. 



A better exposure of it is shown in the eastern side of the quarry 

 at Pouillerel, near Chaux-de-Fonds, where the following section was 

 observed : — 



1. Oxfordien. 



2. Callovien, 10 ft. f b. Blue sandy clays with fossils. 



thick [a. Thin band of ferruginous marl. 



3. Dalle nacree. 



A thicker development of the ferruginous marl occurs in a quarry 

 a little further north, and consists of a brown limestone and marls 

 with ferruginous oolitic grains, 

 from this bed : — 



The following fossils were obtained 



Belernnites hastatus, Blainv. 

 Ammonites hecticus, Rein. 



■ convolutus, Quenst. 



athleta, Phit. 



Nucula ornata, Quenst. 



Lima rigida, Sow. ? 

 Hinnites abjectus, Mor. § Lyc. 

 Terebratula dorsoplicata, Suess. 

 Collyrites ellipticus, Ag. 

 Holectypus, sp. 



The Callovian was also seen below the ' Spongitien ' on the 

 roadside opposite Brenets, as a clayey bed with Bclemnites hastatus, 

 Ammonites convolutus, and A. hecticus. 



The Occfordien Calcaire is divided by Jaccard into : — 



2. Pholadomien. 

 1. Spongitien. 



The 4 Spongitien ' is composed of alternations of limestones and 

 clays, having a total thickness of about 15 metres (49 feet). In 

 some localities these beds contain numerous sponges ; in others, again, 

 such fossils are either absent altogether or very rare. 



In the ' Combe Grede ' this lower division of the Oxfordian consists 

 of grey compact limestones with some marly beds in its upper part. 

 Further west, near the railway-station at Convers, the 'Spongitien' 

 is worked for cement ; the beds exposed in the quarries are thin- 

 bedded, grey, argillaceous limestone with partings of clay. 



Overlying the Callovian, in the quarry at Pouillerel, referred to 

 above, about 10 feet of Oxfordian are exposed, of much the same 



