THE CORALLIAN ROCKS OF ENGLAND. 377 



and small muricated univalves : one of these hard bands, towards 

 the top of the series, has a thickness of 2 ft. 6 in., and exhibits a fine 

 arabesque of shells such as are usually associated with a Rag-fauna. 

 Throughout the series, and especially towards the upper part, a 

 profusion of the spines of urchins may be noted, and the tests of 

 many are from time to time discovered. Pseudodiadema hemispliceri- 

 cum is especially abundant, and may be called the North-Grimston 

 Urchin par excellence. Cidaris Smiihii, Cid. jlorigemma, Hemicida- 

 ris intermedia also occur, the latter frequently. Colly rites bicordatus 

 and Pyg aster umbrella are also quoted from here ; and Echinobrissus 

 scutatus, which swarms in the lower beds, cannot fail to put in an 

 appearance. The remains of the Mollusca in the softer beds are not 

 usually in good condition. Cordate Ammonites, Naticae, Pleuroto- 

 marice, Alarim, and one specimen of Terebratula insignis have to our 

 knowledge been obtained from here. 



In the escarpment also, about 20 ft. below the limestone No. 2, at 

 the point marked c, there occurs in the midst of marly oolites a 

 dense buff-coloured limestone with much spar. It contains corals, 

 both Thecosmilia and Phabdophyllia, along with Pecten vimineus, 

 Modiola inclusa, and spines of Pseudodiadema hemisplicericum. 



These beds then, although partly allied by their lithology to what 

 we must call the Coralline oolite below them, have an undoubtedly 

 Rag-fauna, and present us with what we must consider passage- 

 beds between deposits elsewhere clearly separated. In other dis- 

 tricts, indeed, are found a variety of intermediate deposits between 

 the Coralline oolite with Chemnitzias ( CJiemnitzia-limestoiies), and 

 the Coral Rag with Cidaris florigemma, such as the various shell- 

 beds of Nunnington and elsewhere, or even the "black posts" of 

 the Pickering district ; but these do not so completely exhibit the 

 double-faced character of the Urchin-beds. There is nothing un- 

 precedented, as we have often pointed out, in the presence of corals 

 below the regular Coral Rag ; but for the abundance of Rag-Echino- 

 derms, in an oolitic matrix, we must, in Yorkshire at least, come 

 to the Howardian district only. At the remarkable quarry near 

 Sike Gate, already described, we have somewhat similar conditions, 

 as also in a portion of the limestone series at Coneysthorpe, which 

 is faulted down into the midst of the Lower Calcareous Grit. At 

 certain points, too, along the southern slope of Langton Wold, we 

 meet with exposures proving the existence of similar beds. As the 

 above indications all occur on the extreme southern edge of the area 

 now occupied by Corallian limestones in the Howardian Hills, it 

 leads to the possible conclusion that this great Urchin series is 

 restricted to the southern margin of the formation as developed in 

 Yorkshire. The great abundance of Echinoderms in groups 3 and 4 

 has evidently a kind of connexion with the argillaceous impurities 

 of the limestone. Their profusion in the inter-Coralline clays of 

 Hillmarton is equally remarkable. These same urchins, too, are 

 very abundant in the fine-grained Hildenley limestone, the result of 

 the finest calcareous mud. It is, perhaps, due to this abundance of 

 Echinoderms that we meet with Cidaris florigemma, so to say, before 

 its time. 



