OOLITIC FORMATIONS. 



11 



Pig. 2. 



1. Rubbly limestone (Cornbrasli). 



2. Clay with Terebratulites. 



3. Limestone rock. 



4. Blue clay. 



5. Oolitic rock. 



6. Blue clay. 



7. ' Rag,' or Oolitic limestone. 



8. Sandy bed, containing the ' Stonesfield slate.' 



To this succeed other Lower Oohtes, leading to the Lias. Prof. Sedgwick^ was 

 the first to point out the removal of the upper members' of the OoUtic or Jurassic series 

 from the locaUty, near Oxford, where the above shaft is sunk. 



It may be acceptable to some readers to have a brief statement of the generalisations 

 from the exhaustive survey of mandibular and dental characters of Vertehrata required 

 for an effectual grappling with the question discussed, in 1838, before the Academy of 

 Sciences in Paris and the Geological Society of London. 



The mandible in Mammalia consists of two symmetrical halves or ' rami,' which in 

 some coalesce at the symphysis. Each ramus is a single or continuous bone, and offers 

 a convex or flattened surface for the joint with the cranium ; not a concavity, as in lower 

 Vertebrates. In most placentals the lower and hind part of the ramus projects backward 

 and is called the ' angle.' In some Caruivora {Hyeena crocuta, e.g.) the angle is excavated 

 on its upper and inner surface with a semblance of inflection, but the sharp inner 

 margin is not produced beyond the vertical plane of the coronoid. In the Hare the 

 lower border of the angle expands, so as to project a little beyond both the outer and 

 inner surfaces of the ' ascending ramus : ' viewed from the inner side, it appears to be 

 shghtly inflected. But the inward bending of the part answering to the ' angle of the 

 jaw ' in higher Mammals is peculiar to the Marsupialia, and in some species [Phascolomys, 

 e.g.) to a remarkable extent. 



' 'Trans, of the Geol. Soc.,' 2nd series, vol. iv (1835), p. 26, note. 



