258 



ME. T. EOEEETS OX THE T7PPEE JUEASSIC EOCKS 



As stated above, there are 23 species common to the Oxfordian 

 beds in question and the Corallian of England, and further most of 

 the 21 species which range from the Oxford Clay to the Corallian 

 are more characteristic of the latter than of the former. Of the 23 

 species which occur in the Oxfordian of the Jura and the Corallian of 

 England, 10 are found in the Lower Calcareous Grit, 6 of which are 

 peculiar to that horizon, and 11 out of the 21 species which range 

 from the Oxford Clay to the Corallian have not been found above 

 the Lower Calcareous Grit. The 6 species peculiar to the Lower 

 Calcareous Grit are : — 



Ammonites canaliculatus, Munst. 



Henrici, 1)' Orb. 



Pholadomya concinna, Ag, 



cingulata, Ag. 



Rhynchonella Thuroianni, Br. 

 Millericrinus echinatus, Schl. 



The last-named species is one of the most characteristic fossils of 

 the lower beds of the Corallian of England : in the Jura, however, 

 it passes up from the Oxfordian into the Terrain a chailles siliceux, 

 and the same may be said of Rhynchonella Thurmanni. 



The fauna of the Oxfordian of the Jura has certainly a distinct 

 Corallian fades, and appears to be closely allied to the lower part 

 of the English Corallian. Erom palaeontological considerations, 

 therefore, this stage must be regarded as the equivalent of the 

 Lower Calcareous Grit, together with a part of the underlying 

 Oxford Clay. 



In the southern district of the Jura, 68 species are recorded from 

 the Spongitian (Jaccard, op. cit. p. 209), and 24 from the Pholado- 

 mian (ibid. p. 207). Nine species of the former occur in England, 

 7 of which are Corallian and 2 Oxford Clay. The 24 Pholadomian 

 fossils include 4 British species, 2 coming from the Corallian and 

 the same number from the Oxford Clay. The evidence obtained 

 from these fossils points to much the same conclusions as those 

 arrived at above. 



The Terrain a chailles siliceux has yielded 178 species (Greppin, 

 qp. cit. p. 80) ; as already stated, 55 of these are common to the 

 Oxfordian, whilst 11 pass up into the Calcaire a Nerinees, excluding 

 those fossils which range up from older beds. The fossils from the 

 ' Terrain a chailles siliceux ' include 52 English species, 34 of which 

 are exclusively Corallian, 8 range from the Oxford Clay to the 

 Corallian, and the remaining 10 are Lower-Oolite forms. There is 

 little doubt, therefore, that the ' Terrain a chailles siliceux ' of the 

 Jura is on the same horizon as some part of the English Corailiau. 

 The latter has been fully described by Blake and Hudleston (Q. J. G. S. 

 vol. xxxiii. p. 260), and they have made out the following sub- 

 divisions of these beds (op. cit. p. 389) : — 



6. Supracoralline Beds. 



5. Coral Rag. 



4. Coralline Oolite. 



3. Middle Calcareous Grit. 



2. The Lower Limestone or Hambleton Oolite. 



1. Lower Calcareous Grit. 



