576 



J. F. BLAKE ON THE UPPER 



scutatus and Hemicidaris intermedia. At Westbury the Corallian 

 would appear to be almost absent ; for we must now refer the rubbly 

 beds with Echinobrissus scutatus to the Upper Oxfordian, and the iron- 

 ore itself is nearly, if not quite, Astartian. The ferruginous cha- 

 racter of rocks appears in some way connected with such gaps. In 

 the neighbourhood of Westbrook, Wiltshire, a coral-bed has been 

 described* from which Cidaris florigemma is absent, and which, 

 on that account, is considered older than the usual Eag. This may 

 be so ; but, in view of the similar Eag in the Aube department 

 passing into a true j#oW(/<?mm«-Eag in the Yonne, the difference can- 

 not be of much importance, either here or elsewhere. It certainly 

 need not be considered an Oxfordian reef. At the Calne quarries the 

 lower clays, like those of Hillmarton, abound in Cidaris florigemma, 

 and the bed with Hemicidaris intermedia occurs towards the base ; 

 hence an examination of these quarries alone might lead a foreign 

 geologist to call the freestones Supracoralline ; but the error of such 

 a correlation is easily proved by the overlying coral -growths observed 

 in the heights on the north and south immediately beneath the Kim- 

 meridge Clay. There is little, in fact, in this district to represent any 

 Supracoralline beds. The same is true all the way to Oxford, 

 the ferruginous earth being the only deposit referable to them. 

 The only Corallian rock is the Coral Eag itself, unless we call the 

 great quarries at Wheatley Supracoralline, for which their great 

 resemblance to the limestones of the Ardennes and the Meuse 

 might be an argument. The arrangement of the Yorkshire beds is 

 not very easy, because it is rather difficult to decide which of the 

 beds underlying the Eag should be placed with the Oxford oolite, 

 and which should be associated more closely with the overlying 

 mass. Eeferring to our comparative sections (Q. J. Gr. S. vol. xxxiii. 

 pi. 12), the abundance of Echinobrissus scutatus in the Lower Oolites 

 of Grimston mark them as Oxfordian ; while the " mamillated-ur- 

 chin series," by its Cidaris florigemma, is as plainly Corallian. 

 The Chemnitzia-limestone of Malton is just one of those doubtful 

 deposits to which it is best to apply the name Coralline Oolite. At 

 Pickering the rubbly nature of the base of the Upper Limestones, 

 g, and the introduction there of corals, added to the change of 

 fauna, indicate that the base-line of the Corallian should be drawn 

 almost directly above the Trigonia-beds. It will then be seen that 

 the shell-beds at the top of the Lower Limestones are more con- 

 nected with the uppermost Oxfordian than with the Corallian. As 

 to the Supracoralline beds, they are simply equivalent to the " Upper 

 Calcareous grit," which latter is parallel to the Sandsfoot grit, and 

 not altogether above it as we previously supposed (I. c. p. 390), 

 owing to the non-recognition of the Sandsfoot clay as the equiva- 

 lent of the Coral Eag. 



In the Boulonnais the clays with marly limestones of the Mont 

 des Boucards were first called Oxfordian by Eigaux (33), appa- 

 rently because they seem continuous with the marls below ; but on 

 the discovery of the coral-bearing beds at the base or lower part 

 * Quart. Journ. Greol. Soc. vol. xxxiii. p. 288. 



