240 



MR. T. ROBERTS 0~N THE UPPER JURASSIC ROCKS 



Pterocerian Fossils (continued). 



Pholadomya recurva, Ag 



paucicosta, Ag 



Tbracia incerta. Thurm 



Ceromya excentrica, Ag 



Lucina substriata, Bom 



Cardium bannesianum, Thurm 



axino-obliquum, Thuwn. (cf. dis 



simile) 



Trigonia muricata, Bom 



Mytilus jurensis, Mer 



subpectinatus, U Orb 



Modiola subasquiplicata, Gold/. 



Trichites, sp 



Gervillia tetragona, Bom 



Avicula Gessneri, Thurm 



Lima spectabilis, Contj 



Hinnites maequistriatus, 2?' Orb 



Ostrea semisolitaria, Et 



Terebratula subsella, D" 1 Orb 



humeralis, Bom 



Rhynchonella inconstans, Sow 



semi-inconstans, Et 



Cidaris florigemma, Phil 



Hemicidaris Thurmanni, Ag 



Acrosalenia aspera, Ag 



Holectypus Meriani, JDesh 



o 



a 



O 

 CD 



s 



o 



a 

 © 



3 



O 



O 



* 



* 

 * 



Virgulian. — The rocks of this stage occur only in the western and 

 southern portions of the district, its eastern boundary being a sinuous 

 line running from Soleure to Seprais (Jura Bernois). Greppin (op. 

 cit. p. 115) points out that the northern part of the Jura was under- 

 going upheaval during Pterocerian times, and that land existed in 

 the north-eastern portion of the district under consideration at the 

 time when the Virgulian beds were being deposited; in this way he 

 accounts for the absence of rocks of this stage in the north-east Jura. 



The "Virgulian was at one time well exposed in the neighbour- 

 hood of Porrentruy ; at present, however, the quarries are filled up 

 and no section is visible. A section in these beds at Pichoux is 

 described as follows (Greppin, op. cit. p. 116) : — 



feet. 



Whitish limestones , 65 



Yellowish or grey clays and shelly limestones with 



Exogyra virgula 19^ 



Thick beds of hard compact limestone 65 



Fragments of Virgulian were seen on the surface at Waldeck, 

 near Porrentruy ; they consisted of a reddish-brown limestone with 



