Oh. XX.] OOLITIC STKATA. 413 



in their turn, repose upon the lias in the south and west of England. 

 Among the characteristic shells of the Inferior Oolite, I may instance 

 Terebratula fimbria (fig. 425), Rhynchonella spinosa (fig. 426), and 

 Pholadomya fidicula (fig. 427). The extinct genus Pleurotomaria is 

 also a form very common in this division as well as in the Oolitic sys- 

 tem generally^ It resembles the Trochus in form, but is marked by a 

 deep cleft (a, fig. 428 and 429) on one side of the mouth. The Col- 

 ly rites ringens (fig. 430) is an Echinoderm common to the Inferior 

 Oolite of England and France, as are the two Ammonites of which 

 representations are here given (figs. 431, 432). 



Fig. 432. Fig. 433. 



Ammonites BraikenHdgvi, Sow. Ostrea Marshii. \ rtat. size. 



Oolite, Scarborough. Middle and Lower Oolite, or ranging 



Inf. Ool., Dundry ; Calvados ; &c. from Coral Bay to Cornbrash. 



Palceontological relations of the Oolitic strata. — Observations have 

 already been made, p. 345, on the distinctness of organic remains of 

 the Oolitic and Cretaceous strata, and at pp. 398 and 401 of the 

 proportion of species common to the Upper and Middle, and to the 

 Middle and Lower Oolite. Betweenthe latter and the Lias there is a 

 somewhat greater break, for out of 120 mollusca of the Upper Lias 13 

 species only pass up into the Inferior Oolite. Professor Ramsay has call- 

 ed our attention to an important generalization not yet alluded to, name- 

 ly, that there are at present wider breaks between some of our minor sub- 

 divisions, and especially between the Inferior and the Great Oolite, palse- 

 ontologically considered, than between what we generally regard as 

 divisions of a higher order, such as the Lower, Middle, and Upper 

 Oolites. Thus, for example, there are, according to Mr. Etheridge's 

 tables, 518 species of mollusca known in ^he Great Oolite and 370 in 

 the Inferior, and of these only 93, or about 12 per cent., are common 

 to the two ; and, what is very remarkable, of 39 species of Cephalopoda 

 known in the Inferior Oolite, only one passes upwards into the Great 

 Oolite, namely, Belerftnites giganteus, and it has been questioned by 

 some palaeontologists whether even this Belemnite has really been 

 found in the Upper of the two formations. This distinctness of the 

 Cephalopoda is the more striking, because both the Great and Inferior 

 Oolites are calcareous formations, and we cannot, therefore, account 

 for the difference of species by any marked dissimilarity in the nature 

 of the sea-bottom. As to the intervening Fuller's Earth, it affords us 



