THE C0RALL1AN ROCKS OP ENGLAND. 341 



soluble bicarbonate, which is again precipitated as calcic carbonate 

 amongst the interspaces of the slowly settling mud, thus cementing 

 the whole into a mass of most compact rock, and gluing up all the 

 shells. 



We now proceed to trace the several subdivisions seen in the section 

 at Pickering and the gorge of Newtondale behind it, as they are mo- 

 dified at various localities to the east and west within the district. 



The Lower Calcareous Grit. — This and the overlying limestones 

 are the only members of the series that, to our knowledge, pass 

 across to the Scarborough district. It presents no points of great 

 interest, though strati graphically it is of importance. The moorland 

 streams that, cutting down to the Oxford Clay, force their way south- 

 wards through the overlying strata to join the Derwent, have their 

 steep flanks formed by the sandy beds of this division; and not seldom 

 we meet with dry sandy gashes, presumably due to a kind of subter- 

 ranean denudation, the streams, instead of keeping upon the surface, 

 sinking through the porous rock to come out as springs. The 

 uppermost beds almost invariably have large cannon-ball doggers in 

 them, to which those at Filey bear about the same relation that a 

 68-pound shot does to a 13-inch shell. These doggers are not very 

 fossiliferous, but occasionally contain Ammonites perarmatus, Perna 

 quadrata, Pecten jibrosus, and Rhynchonella Thurmanni. The most 

 accessible spot where the Lower Calcareous Grit may be studied is 

 in the neighbourhood of Allerston, on the Pickering and Scarborough 

 road, where at the mouth of Givendale several quarries, some showing 

 a face of from 40 to 50 feet, are worked for free-stone. 



The Lower Limestones and Middle Grit. — We take these together 

 because the sections illustrative of one often elucidate the other. 

 Coming from the east, we first see these limestones graduating through 

 tho passage-beds into the Lower Calcareous Grit, itself traceable 

 down to the Oxford Clay, at the mouth of Oxdale near Allerston, in a 

 large quarry about the 400-foot contour (dip about S.W.). The oolites 

 of the Lower Limestones have a face of about 30 feet. A note- 

 worthy feature is a line of intermittent corals (Thamnastrcea) of 

 large size quite in the oolite, and tuberous masses of silicified oolite 

 towards the base. These peculiarities are also well observed in the 

 next-described quarries on the hill east of Thornton. These are 

 excavated wholly in these limestones at different levels. In one of 

 these quarries we have the following section : — 



Section in the Further Quarry East of Thornton Dale. 



feet. 



1. Fine-grained oolites, measured down to a line of intermittent 



coral ( Thamnastrcea) , partly silicified 14 



2. Oolitic limestone of similar character 1 L 



3. Stronger-bedded oolitic limestone, with tuberous and spherical 



masses of silicified oolite 3 



28 

 These coral masses are of excessive interest, as being on an horizon 



