THE CORALMAN BOCKS OF ENGLAND. 323 



limestones of varying degrees of purity with but little intervening 

 grit, a sequence not to be met with perhaps in an equal space in 

 any other locality. If we are to find the representative of the 

 " Filey-Brigg Calcareous Grit " here, it must be in some portion of 

 the Intermediate Series, whose equivalents both to the east and 

 west contain a greater amount of arenaceous matter. 



The next step is to trace the development of the several portions 

 of the series here indicated, as they occur elsewhere in the Scar- 

 borough district. 



The Lower Limestones. — To the east of the Derwent Gorge the 

 basement beds on their outcrop are so markedly ferruginous as to be 

 easily traced ; and this is a fortunate circumstance, as they constitute 

 a reliable datum line. Following the outcrop towards Scarborough, 

 we find them as flaggy ferruginous limestones, used for walling, and 

 much made up of broken shells — the Hackness type. On Irton 

 Moor, where they crop out, we noted Ammonites Williamsoni and 

 Avicula expansa. 



It is just possible that towards the base of the Lower Oolite 

 there may be, in places, a slight development of a Lower Coral 

 Bag, such as we shall see to be the case at Hackness in a similar 

 position. These indications should be sought in the high plateau 

 east of the line of section, where the beds crop out in succession. 

 The fields hereabouts contain Spongia floriceps, and curious lumps, 

 such as may frequently be noted in fields having corals under- 

 neath. The characteristic fossils of this horizon, towards the base 

 of the Lower Oolite, such as Cylindrites elongatus, Gervillia avicu- 

 loides, and Khynchonella Thurmanni, may be noted in a small 

 quarry of greyish limestone. This is probably the outcrop of the 

 beds towards the base of the "White Quarry" (fig. 11). Further 

 eastwards there are no very definite indications whereby we can 

 judge the character and value of the Lower Oolite. 



The section on Scarborough Castle Hill (fig. 12), though imperfect 

 towards the top, is, however, an exception, as it exhibits the Lower 

 Limestones very well indeed. 



The close correspondence between this section and that of Forge 

 Valley is remarkable, the thickness and general development of the 

 several subdivisions being well maintained. Commencing our com- 

 parison bove the ball-beds, we have (B. 6, 17 feet) the " red 

 beds," evidently the equivalents of e' of the Forge-Valley section. 

 Their ferruginous character is still maintained at Scarborough ; but 

 the petrology is more that of the Hackness type. The next series 

 (B. a, 11 feet) corresponds to e of the Forge- Valley section, and 

 contains the characteristic fauna of this horizon. But it happens 

 here at Scarborough to be unusually rich, containing some very 

 shelly beds, from which the following are amongst the snecies which 

 have been determined : — 



y2 



