248 



ME. T. ROBERTS ON THE UPPER JURASSIC ROCKS 



of quartz scattered about the surface of the ground, which had 



been washed out of the clay. The clayey beds with carbonaceous 



material and gypsum were seen in the railway-cutting near Locle. 



Marly beds of Purbeckian age were also observed north of Ste. 



Croix ; and further south, near Vallorbes, the following section 



occurs : — 



3. Valangian. 

 2. Purbeckian: — 



(d) Vesicular aud some compact limestones. 



(<?) Compact grey limestone. 



(b) Scoriaceous limestone. 



(a) Grey marls. 

 1. Portlandian. 



The section on the road towards Yalangin, already referred to, 

 was also visited ; and here again the succession was not clear, but 

 the beds of Purbeckian age which were seen consisted of grey lime- 

 stones and marls. 



The Purbeckian of the Jura is said to be conformable to the Port- 

 landian beds below, and to pass up without any physical break into 

 overlying Valangian ; and our own observations support this view. 



Prom the description of the beds in the two districts under con- 

 sideration it will be seen that the various stages differ considerably 

 in their lithological character and, to some extent, in their fossil 

 contents. On account of these differences it is not always easy to 

 correlate exactly the beds in these two parts of the Jura. In the 

 accompanying Table (p. 249) a correlation is given which is pro- 

 bably approximately correct. 



In both areas we find the Callovian underlain by the ' Dalle 

 nacree.' The Callovian itself is, as already stated, but feebly repre- 

 sented in the southern district, and the Per sous-oarfordien, so well 

 marked in the northern parts of the Jura, is scarcely represented in 

 the Central Jura, unless it be by the clayey bed in the upper part 

 of the Callovian, which sometimes contains pyritous nodules. 



In the ' Combe Grede,' near St. Imier, where the Callovian consists 

 of a thin cherty band, the Callovian of the northern district may be 

 represented in part by the uppermost portion of the ' Dalle nacree.' 



The Oxfordian presents much the same palaaontological character 

 in both districts, and the correlation indicated in the table is, as 

 far as can be gathered from the study of the fossils, correct. 



The Corallian of the southern district, according to Desor and 

 Gressly (' Etudes Geol. sur le Jura Neuchatelois, p. 75), represents 

 only the Terrain a chailles siliceux of the Northern Jura, and they are 

 of opinion that the Oolithe corallienne and Calcaire a Nerinees are 

 wanting in the Jura Neuchatelois. About 50 per cent, of the 

 fossils from the Corallian of the Central Jura are found in the Terrain 

 a chailles siliceux, whilst only about 8 species (out of 54) occur in 

 the Oolithe corallienne of the Northern Jura, and most of these 

 appear also in the Terrain a chailles siliceux. It is highly probable 

 therefore that the correlation given by Desor and Gressly is correct. 

 If this be the case, the question arises whether any part of the 

 Astartian of the southern district is the equivalent of the Calcaire 



