THE CORALLIAN BOOKS OF ENGLAND. 339 



may be described as a grey ferruginous limestone. Numbers of small 

 shells, such as Ostrea, Nerincea, and, possibly, Littorina muricata 

 and Pecten intertextus, mixed with flatted sphericles, seem compressed 

 into a grey and somewhat sparry matrix of considerable density. On 

 account of the abundance of iron and alumina in its composition, it 

 is much prized for smelting-purposes. Although this bed occupies 

 the position of the Coral Rag, no flints, recognizable spines of Cidaris 

 Jlorigemma, or other well-known indications of that class of rock occur* 

 If, however, we trace it backwards on the rise, we find it passing 

 into, and inosculating with, a Rhabdop7iyllia-~R&g in the fourth 

 quarry on the west side ; so that its relations are undoubted. 



c, 4 feet. — By the incoming of beds which gradually prepare us 

 for the true Kimmeridge Clay, we have an unmistakable intimation 

 that, within the area at present under description, Corallian lime- 

 stones are not be found above this horizon. On the planed-down 

 surface of the false-bedded series last-named reposes that very 

 curious bed locally known as the " throstler." It is a kind of 

 sandy argillaceous limestone, of peculiar texture, with few, if any, 

 recognizable fossils, but having numerous copper-coloured specks 

 which probably represent fragments of shells now replaced by iron- 

 oxide. In the first quarry on the west side there is just a little 

 hummock of it interposed as a lenticular mass between b and d. In 

 the second quarry on that side a 6-inch layer of dirty flaggy lime- 

 stone probably represents it ; while in a quarry at the back of the 

 main ones it is about 2 feet thick, is undulated by 4 inches of lamina- 

 ted soft sandstones, and appears to contain remains of Polyzoa. On 

 the east side it is fully 4 feet thick. 



a and 6, 17 feet. — These complete the series of rocks intervening 

 between the Upper Limestones and the true Kimmeridge Clay, 

 which may be seen capping the hills above one of the quarries on 

 the west side. They are there, however, less favourably exposed 

 than on the east, whence our descriptions and thicknesses in the 

 generalized section are taken. The upper, or " red rock," is the 

 most remarkable. It is a true calcareous grit, and maintains its cha- 

 racters throughout this district and even on the Hackness outlier 

 already described. Indeed these characters are so marked that there 

 is no mistaking the rock when once seen. In exposed portions it is 

 almost devoid of lime, and is full of " pinhole " structure, with soft 

 parts adhering to the harder cores ; but it differs from the Lower 

 Calcareous Grit in being exceedingly sharp and gritty, as if every 

 particle were angular and stood out by itself. It is highly charged 

 with tuberous and dichotomizing forms, which, in their enormous 

 proportions, almost exceed those of the Lower Calcareous Grit. The 

 fossils are abundant and varied; but most of them being in casts, their 

 identification is not entirely satisfactory. Attention should be 

 drawn to the remarkable layer of Ostrea bullata at the base of the 

 sands. 



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