384 J. P. BLAKE AND W. H. HUDLESTON ON 



ferruginous marls. This nearly total absence of higher beds and 

 the comparatively feeble development of any beds but those con- 

 taining Cidaris florigemma above the Lower Calcareous Grit is the 

 chief feature here. 



At Highworth (Section VII.) we enter on a new phase, which 

 continues nearly constant as far as Marcham, i. e. while the escarp- 

 ment faces north. The peculiarity here is the development below 

 the Rag with Cidaris florigemma of wonderfully fossiliferous lime- 

 stones, in which such shells as Trigonia Meriani, Lima rigida, Am- 

 monites pJicatilis are abundant ; they also contain corals in the lower 

 part, and are capped, here and there, by false-bedded oolitic sandstones. 

 These beds, which may fairly compare with the Coralline Oolite of 

 Yorkshire, are continuous beneath the rag, which sometimes rests 

 upon them directly and at others is separated by more arenaceous 

 beds. The true ferruginous Upper Calcareous Grit succeeds 

 the Rag in the direction of the dip, but in an easterly direction 

 entirely disappears, so as to be quite absent at Oxford. These re- 

 markable shell-beds disappear on approaching Oxford by Cumnor, 

 at which latter place the Coral Rag, in a magnificent form, lies 

 directly on the Lower Calcareous Grit. At Oxford itself, however, 

 or rather at Headington (Section VIII.), another shell-bed appears, 

 with abundance of Cidaris florigemma and other fossils usually asso- 

 ciated with it in the Rag, proving it not to be the Highworth bed 

 again, but a more recent one. Here the rag inosculates with, and 

 is overlain by a thick mass of false-bedded comminuted shell-lime- 

 stone, which assumes enormous proportions at Wheatley, the whole 

 formation above the Lower Calcareous Grit varying between marls 

 and limestones, and finally disappearing at this point. 



It is in this range that the whole series is reduced to a minimum, 

 the last remaining members being the Lower Calcaieous Grit and 

 the Coral Rag proper, and these in places being of no great thick- 

 ness. It is here also that we meet with the greatest variety of 

 type within the same area, which we have endeavoured to indicate 

 in figure 8. 



The Cambridge Beef. — The only members here recognized (Sec- 

 tion IX.) are the Coral Rag, here with an abundant and special 

 fauna, but with sufiicient of the characteristic species to connect it 

 indissolubly with the ordinary Rag with Cidaris florigemma^ aud the 

 apparently underlying and less fossiliferous Oolite. The nature of 

 the ground is not such as to enable us to learn more of the real 

 thickness of these than is seen in the quarries, nor the nature of 

 the underlying rock. The Elsworth rock we take to be an ex- 

 ceptional development of the Lower Calcareous Grit. 



The Yorkshire Basin. — If we except the fine series at Weymouth, the 

 Corallian rocks in this district present an incomparably finer develop- 

 ment than in any other, and constitute not a mere string of rocks, but 

 a veritable massive,whose area, circumference, and maximum thickness 

 are severally almost equal to those of all the other areas put together. 

 Although we have divided the basin, for the purpose of detailed 

 description, into several parts, we may here consider it as a whole, 



