﻿FRAAS ON THE JURA FORMATION. 



63 



from these quarries are worked out of the Great-oolite, and in order to 

 get to them, the Forest-marble, of 10-12 feet thickness, is removed ; 

 the latter is here filled with Corals, Echinodermata, and Apiocrinites. 



In the south of England the Great Oolite is in force, presenting 

 all the varieties of the rock ; and at several localities it is rich in 

 small and elegant shells. This is the case near Bath, Stonesfield, 

 &c. Hence the name " Bath Oolite," which the French adopted, 

 because even on the other side of the Channel the same stratum is to 

 be found, near Luc for instance. This bed is a local formation of the 

 Great Oolite ; it is a snow-white, soft, oolitic limestone, very inco- 

 herent, and consisting almost entirely of shells and fragments of 

 shells. This bed can be best observed between Luc and Langrune, 

 three leagues north of Caen, near the sea-shore. The tide here eats 

 into the shore, and the ebb-tide clears away the debris ; towards the 

 top of the 20-25 feet thick bed we find an immense abundance of 

 Terebratulce ; T. digona, T* biplicata, T. reticularis, T. plicatella, 

 T. concinna ; also Echinodermata, as Ilemicidaris, Echinus, Gale- 

 rites, &c. ; further down, there is a bed of bivalves, generally with 

 the valves separate, such as Nucula, Area, Lima, Corbula, &c. The 

 whole bed is interlaced with Corals, with a strong base of Astrcea, Mce- 

 andrina, Lithodendron, Madrepora, and Scyphia ; Serpulce are found 

 in great quantities upon the shells, which are often entirely covered 

 with parasites ; small Gasteropoda and Patellce are also present. On 

 the other hand, the Cephalopoda seem to have become extinct, not 

 a trace of them being found. Upon this local deposit of the Bath 

 Oolite, there appears in the south of England another local forma- 

 tion, the " Bradford Clay," situated between the Great Oolite and 

 the Forest-marble, full of the most beautiful fossils ; this bed, how- 

 ever, does not find any parallel in other countries. In Wiltshire, 

 especially in the neighbourhood of Bradford, we meet with a quantity 

 of grey unctuous clays, with their organic remains in a most perfect 

 state of preservation. Here are found Apiocrinites intermedins, A. 

 rotundus, A. elongatus, A. dichotomies, with crown, stem, and root ; 

 also Terebellaria ramosissima, Avicula costata, Terebratula coarc- 

 tata, T. concinna, T. digona, Serpula triangulata, Lima, Gervillia, 

 Modiola, Cidaris, and others. The Forest-marble rests on the top 

 of the Bradford clay. Stonesfield, already famous for its Great Oolite, 

 exhibits a fine development of this stratum also [?] ; we here find 

 Clypeus and Galerites, Millepora straminea and Ceriopora, Trigonia 

 pullus, Pecten similis, Modiola imbricata, Ostrea, Pleurotomaria, 

 &c. But this bed already shows evidence of the general inclination 

 of the English Jura to form sandstone, and at many places we find 

 the hard marbles replaced by clay- and sand-beds. Towards the 

 north especially do these sand-beds gain in force (Upper sand), in 

 which Pentacrinites vulgaris and Plants are abundant. The sand- 

 stones in the Forest-marble of Wiltshire, near Castlecombe, fre- 

 quently bear the markings of the tracks of small animals upon their 

 greyish yellow lamin£e. In Yorkshire these sandstones obtain at last 

 such a development, that they surpass the whole Great Oolite for- 

 mation, and resembling the " lower coal," now hold a separate place, 

 as " upper coal" or " upper moorland sandstone," containing innu- 



