414: PAL^ONTOLOGICAL RELATIONS. [Ch. XX, 



but little information in regard to the condition of marine life, hav- 

 ing yielded at present only 22 mollusca, as before mentioned (p. 412). 

 While, therefore, the break between two great members of the Lower 

 Oolite is expressed by saying that the proportion of species in common 

 only amounts to 12 per cent., we have seen that there is a connection 

 of 24 per cent, between the Upper and Middle, and 21 per cent, be- 

 tween the Middle and Lower Oolite ; hi other words, there is twice as 

 great a connection between our larger divisions as between two separate 

 members of one of them. * 



In illustration of shells having a great vertical range, it may be 

 stated that in England 4 species, and 4 only, are known to pass up 

 from the Lower to the Upper Oolite, namely, Rhynchonella obsoleta, 

 Lithodomus inclusus, PJioladomya ovalis, and Trigonia elongata. • 



Of all the Jurassic Ammonites of Great 

 Fig. 434 Britain, A. Macrocephalus, Schloth, which is 



common to the Great Oolite and Oxford Clay, 

 has the widest range. 



That most of the sudden changes of species 

 were due to migration, may be inferred, as 

 Prof. Kamsay remarks, from the fact that, after 

 disappearing from an intermediate formation, 

 Ammonites macrocephalus, tne y often reappear in a higher one. But the 

 Schioth. | nat. size. phenomena, on the whole, indicate a constant 



Great Oolite and Oxford -> . , £ .. . ,. . -, 



Clay# dying out ot preexisting species and a coming 



in of new ones. We have every reason to con- 

 clude that the gaps which occur, both between the larger and smaller 

 sections of the English Oolites, imply intervals of time, elsewhere 

 represented by fossiliferous strata, although no deposit may have 

 taken place in the British area. This conclusion is warranted by the 

 partial extent of many of the minor and some of the larger divisions 

 even in England. " Thus, the Inferior Oolite," says Prof. Ramsay, 

 " attains its maximum development near Cheltenham, where it can 

 be subdivided into at least three parts. Passing north, the two lower 

 divisions, each more or less characterized by its own fossils, disappear, 

 and the rag-stone, northeast of Cheltenham, lies directly upon the 

 Lias, apparently as conformably as if it formed its true and immediate 

 successor. In Dorsetshire^ on the coast, the series is again perfect, 

 though thin. Near Chipping Norton, in Oxfordshire, the Inferior 

 Oolite disappears altogether, and the Great Oolite, having first over- 

 lapped the Fuller's Earth, passes across the Inferior Oolite, and in its 

 turn seems to lie on the Upper Lias with a regularity as perfect as if 

 no formation anywhere in the neighborhood came between them. In 

 Yorkshire the changed type of the Inferior Oolite, the prevalence of 

 sands, land-plants, and beds of coal, leave no doubt of the presence 

 of terrestrial surfaces on which the plants grew, and all these phe- 

 nomena lead to the conclusion that various and considerable oscilla- 

 tions of level took place in the British area during the deposition of 





