THE CORALLIAN ROCKS OF ENGLAND. 337 



</, 13 feet. Fig. 14 is a portion of the general section, enlarged for 

 the purpose of exhibiting the peculiarities noticed about the junction 

 of these two groups. It represents the appearances on the west rather 

 than on the east side. We have already referred to it as showing 

 the mode of occurrence of the Trigonia-beds, and the argillaceous 

 representative of the " small shell-bed." Although both the groups 

 (h and g) may be deemed passage-beds, their petrology linking them 

 with the calcareous grits, whilst their palaeontology draws them to- 

 wards the oolites, yet in g we very soon lose all traces of grit (an 

 important physical difference) and obtain, along with corals, some 

 change in the fauna ; hence we consider the Coralline oolite of 

 Pickering to commence at the base of this series. The beds classed 

 in group g are variable and impure limestones, mostly used for road- 

 metal. At its base is the thin and very variable bed /3 of the enlarged 

 section (fig. 14) which also forms in an irregular way the top Tri- 

 gonia-bed ; it is most generally a discoloured oolite, chiefly charac- 

 terized by a quantity of Nerincea visurgis (large) and Astarte Du- 

 boisiana, and contains also Pema mytiloides and Pecten Jibrosus. 

 Above this, and sometimes perhaps included in the base of it, is 

 the great block locally called " "Wilf," which comprises the whole of 

 a (fig. 14). It is sometimes divisible into as many as three minor 

 blocks, and is a complete mixture of every thing; corals may be noted 

 both at the bottom and at the top, and possibly also in some parts of 

 the central mass. Isolated groups of Thamnastrcea arachnoides appear 

 to have grown upon the top of the last bed of calc-grit ; then came 

 a shell-drift with Trigonia-Y&lxes, Astarte Duboisiana &c, then 

 mixtures of calc-grit, and oolite, another string of shells, then some 

 more decided oolite, with very fine Nerincea visurgis, mixed with 

 some' more Thamnastrcea arachnoides. Some parts contain so much 

 coral as to present the appearance of a Coral Rag, but without the 

 fauna of the true Rag. 



Returning now to the general section, the block above this con- 

 tains impure, and often blue-centred limestones ; but is most re- 

 markable for a band of pisolite, which may readily be proved in all 

 the quarries. This pisolite contains the same Nerincea and Astarte 

 as below ; and Trigonia perlata, along with some of the other fossils 

 of the Trigonia-heds, continues to be met with sparingly. Immedi- 

 ately above the pisolite is an extremely compact limestone, in texture 

 almost like china-stone, with a few very small, round, oolitic granules. 

 It is curiously marked by the sparry shells of small Cerithia (C. 

 inornatum ?) and of Nerincece, so thoroughly sealed into the rock as to 

 afford no hope of extraction or of specification. Fine-grained rocks 

 are often associated with small shells, and coarse-grained rocks with 

 large ones. In this case the mechanically-derived sediment, which 

 is by no means inconsiderable, is of the finest texture. In the next 

 block we have the succeeding group prefigured, Chemnitzia hedding- 

 tonensis beginning to prevail in the upper part : here also are many 

 examples of Phasianella striata, often of immense size. In the quarries 

 further north in the direction of the outcrop, the character of theso 



Q.J.G.S. No. 130. z 



