JURASSIC OF THE PARIS BASIN". 



525 



dian, though the facies is too different to permit us to compare it 

 directly with the portion of the English Kimmeridge Clay corre- 

 sponding to it. The next portion of the series, called by Tombeck 

 the zone of Gyprina Brongniarti, consists of three subdivisions, each 

 of which has sufficiently marked lithological characters to be recog- 

 nized without fossils ; and they are admirably shown to the north of 

 Joinville. The thickness of this portion is estimated at 160 feet, and 

 it is far more fossiliferous than the lower group, as we have seen it 

 to be near Bar-le-Duc. Still the line between the two may be con- 

 sidered arbitrary, and very probably does not correspond to the 

 subdivisions in the Department of the Yonne. Pinna suprajurensis, 

 after which the series is named in that locality, occurs here in 

 abundance in some beds above the Bure Oolite, which are not cari- 

 ous. The whole is well seen above Rachecourt, as Tombeck says. 

 The chief fossils observed in this series are Gyprina Brongniarti, 

 Mytilus icaunensis, Anatina incequilatera, Corbula mosensis, Gardium 

 Dufrenoycum, Gyprina implicata, Pecten nudus. These beds are 

 here better developed than in the Meuse, and yield more data for 

 comparison. They are succeeded by a small thickness of unfossili- 

 ferous, dirty-coloured stones, which form the possible representative 

 of the " Middle Portland " of Boulogne. 



Above all these rocks, and seen in several places to continue 

 without discordance into them, are the remarkable beds placed as 

 the " Zone of Gyrena rugosa" They partly consist of grey flags, 

 sparkling with minute crystals and crowded with Corbula! infleoca, 

 and partly of vacuolar oolite, worked in thick beds free from fossils, 

 having here and there bands of shells, the principal of which are 

 Astarte rugosa, Corbula injiexa, and Avicula rhomboidalis . The 

 beds have the appearance of having been formed in shallow water. 

 These rocks, of which the 16 feet worked at Chevillon may be a 

 maximum, appear to be separated from all below them, both in 

 character and the greater number of the fossils ; and under these 

 circumstances, perhaps, the single shell (Astarte rugosa) which they 

 have in common may suffice for a bond of union with the English 

 Portland rocks. The development here is extremely restricted, these 

 rocks not having a range of more than 30 miles. 



4. Department of the Aube. — We here come under the guidance of 

 Leymerie (7), whose work, though now old, is admirable ; and very 

 little attention appears to have been paid to the department since 

 his time. His classification of the rocks is as follows : — 



Upper Jurassic. 



1. Portland limestone, 330 feet. 



2. Marls and limestones, with Exogyra virgula, 250 feet. 



Middle Jurassic. 



1. Astartian limestone, 320 feet. 



2. Nodular white limestones = Coral Eag, 40 feet. 



3. Lower Coral limestone. 



a. Compact limestone, 80-100 feet. 



b. "Levique" limestone, 50 feet. 



c. Oolitic shell-limestone, 80-100 feet. 



