ON THE UPPER JURASSIC ROCKS OE THE SWISS JURA, ETC. 



229 



21. On the Correlation of the Upper Jurassic Eoces of the Swiss 

 Jura with those of England. By Thomas Eoberts, Esq., M.A., 

 F.G.S., "Woodwardian Museum, Cambridge. (Read January 

 26, 1887.) 



In the summer of 1884 the author was sent out by the University 

 of Cambridge, with a grant from the Worts Eund, to study the 

 Jurassic rocks of the Jura. He was accompanied by Mr. E. W. 

 Small, M.A., Christ's College. Some of the results then obtained 

 are given in the present paper. 



The Jura range of mountains is formed in great part of rocks of 

 Jurassic age, which have been thrown into a series of folds running 

 more or less parallel to each other in a north-east and south-west 

 direction. These folds are usually quite simple, and it only rarely 

 occurs that the foldings have gone on to such an extent that the 

 beds are inverted. 



If one examines a geological map of the district, it will be seen 

 that thesur^ce of the ground is occupied principally by Upper 

 Jurassic^Kocks ; indeed all the higher ground is so formed, and it is 

 only in the valleys and gorges which run transversely across the 

 folds, or in the centre of the folds where the upper portion has 

 been removed by denudation, that older beds are seen. 



In this paper it is proposed to deal only with the Upper Jurassic 

 Eocks. In this term are included all the beds which lie between the 

 base of the Callovian and the summit of the Purbeckian, and as 

 such it is generally understood by English geologists. This classi- 

 fication, however, differs from that given by many foreign authors, 

 since what is here included in the Upper Jurassic is equivalent to 

 their Middle and Upper J urassic. 



It is proposed to give, first of all, a general description of these 

 rocks as seen in the district visited, and then to attempt their corre- 

 lation with the Upper Jurassics of England. The Jura itself has 

 been fully described by Swiss geologists and others, and the follow- 

 ing memoirs refer more particularly to the geology of the portion of 

 the Jura with which it is proposed to deal : — 



(1) Greppln, J. B. Essai geologique sur le Jura Suisse. Dele- 

 mont, 1867. 



(2) Greppln, J. B. Materiaux pour la Carte Geologique de la 



Suisse (Jura Bernois et districts adjacents). Berne, 1870. 



(3) Jaccard, A. Materiaux pour la Carte Geologique de la 



Suisse (Jura Yaudois et Neuchatelois). Berne, 1869. 



(4) Desor and Gressly. Etudes Geologiques sur le Jura Neu- 

 chatelois. 



A complete list of papers on the geology of the central part of 

 the Jura is given by Jaccard (op. cit. p. 331). 



