THE CORALLIAN ROCKS OF ENGLAND. 385 



the varying structures of different localities being well illustrated 

 by our sections X.-XIY. 



The Lower Calcareous Grit has a far more constant and regular 

 development than the other formations, and, as a mass of solid 

 rock, attains an importance not observed in the south. In the 

 Howardian Hills (sections X., XI.) the thickness is about 60 feet, 

 chiefly in layers of buff freestone and hard blue rock. In the 

 western and northern hills (XII., XIII.) the thickness is increased 

 to 100 feet, all solid rock. In the eastern districts the top part is 

 marked by ball-beds. 



In connexion with the Corallian limestones the chief feature of 

 interest is the double group so well marked in the Tabular 

 Hills. Along the coast, where the lower beds are so admi- 

 rably displayed, this duplicate series is by no means obvious, 

 and requires to be interpreted by the light of exposures in the 

 interior. The section at Filey still remains somewhat problematical ; 

 but we have reason to presume that the two limestones are there 

 continued in an altered and more arenaceous form, and that the 

 Filey-Brigg Calc-Grit is the representative of the Middle Calcareous 

 Grit, although elsewhere in the Scarborough district this sub- 

 formation is but feebly developed. As Filey Brigg is the most 

 easterly point of the Corallian area in Yorkshire, the character of 

 the rocks seems to indicate a lessening of calcareous matter in that 

 quarter ; so that possibly the Corallian deposits may have had their 

 original termination in a south-easterly direction, not very far from 

 the existing coast. The limestones generally in the Tabular Hills may 

 be said to have a lenticular development, attaining their maximum 

 along an east-and-west line which, in the Scarborough district, is 

 not very far from the roots of those hills. The non-appearance, 

 therefore, of particular beds may be due, in some cases, to thinning 

 out rather than to denudation. The limestones of Scarborough 

 Castle Hill clearly belong to the lower group alone ; and this section 

 is therefore more imperfect than that at File}''. 



The fauna of the Lower Limestones, inclusive of the passage- 

 beds, has much in common with that of the Lower Calcareous Grit. 

 This is especially marked in the eastern districts, where alone we 

 have been able to procure much fossil evidence. The purer oolites 

 are generally very poor ; but towards their base occasional shell- 

 beds produce a characteristic set of Brachiopoda, which, with a 

 great abundance of Qervillia and, in certain lines, of Cylindrites, 

 may be said to mark them. There are peculiar phases of the pas- 

 sageTbeds, however, which are an exception to this poverty, such 

 especially as that above the Ball-beds at Filey, and a very similar 

 rock in an analogous position at Appleton. In such places Brachi- 

 opoda seem to be unusually abundant, especially Rhynchonella Thur- 

 manni ; and these are associated with a tolerably numerous set of 

 Conchifera, along with Millericrinus echinatus, Acrosalenia decorata, 

 and, at Appleton, with Glyphea, some of the same species oc- 

 curring, though less plentifully, in the Lower Calcareous Grit itself. 

 Cordate Ammonites, especially of the Ooliathus type, are prominent 



Q. J. G. S. No. 130. 2 c 



