THE CORA.LLIAN ROCKS OF ENGLAND. 389 



causes acting in isolated areas, and at periods which may, indeed, 

 coincide in point of order, but not necessarily in point of time. It 

 is only in such a sense as this that we can attempt any thing like 

 correlation, or arrange the whole series in a chronological sequence. 

 It is undoubtedly to Yorkshire that we must go for our type 

 with which to compare the rest, and thence take our general 

 names. 



The Corallian deposits, then, may be considered, when complete, 

 to be represented by the following series, in ascending order : — 



1. The Lower Calcareous Grit. — This may have begun earlier in 

 some places than in others. If we judge by the thickness of the 

 Oxford Clay below, we should suppose it to have begun very early in 

 the Tabular Hills, but not very early at Weymouth. In the latter 

 place it is represented by the Nothe grits ; and in the other districts 

 there is no difficulty in its recognition. 



2. The Lower Limestone or Hambleton Oolite. — This mass, which 

 is so intimately connected by its fauna with the Lower Calcareous 

 Grit, may be represented elsewhere than in Yorkshire by some 

 portion of the latter ; but its place is nowhere recognizable in the 

 south, unless it be, 1st, near Sturminster, in the oolites which under- 

 lie the pisolites, and, 2nd, at Weymouth in the Nothe clays. 



3. The Middle Calcareous Grit. — This also is nearly peculiar to 

 Yorkshire, unless, having placed the Nothe clays on the horizon of 

 the Hambleton oolites, we take the Ben cliff grits to represent this 

 in the Weymouth area. 



4. The Coralline Oolite. — This is the mass of limestone which is 

 developed beneath the Rag, and with which it has been usually con- 

 founded. It is well marked in Yorkshire as a massive limestone; 

 we take the oolite in Upware north pit to represent it in the nearest 

 locality to Yorkshire. Its equivalent begins again to the west of 

 Oxford, and reaches to beyond Highworth, at which place and at 

 Faringdon are fine developments of what we would correlate with 

 it. At Calne it appears as a marl, and at Steeple Ashton and 

 Westbury under both forms, the marl being below. The marls 

 and false-bedded series of the North-Dorset district appear to 

 belong here. In the Weymouth area the Osmington oolites re- 

 present the lower portion, and the Trigotiia-beda the upper 

 portion. 



5. The Coral Rag. — Though there is a lower Coral Hag at 

 Hackness and at Highworth, there is no danger in using this in its 

 strict lithological sense; for, with these exceptions, the development 

 of Corals uniformly represents the same term in the series. They 

 are usually, but not universally, associated with Cidaris Jiorigemma, 

 which makes the term " Florigemma-r&g " or " zone " sometimes 

 convenient, since by this fossil in the absence of corals the cor- 

 responding beds may be most easily recognized. We note that the 

 Ayton-Brompton Rag does not contain it. At Grimston we have 

 the Urchin-beds below, which must be included with this. At 

 Upware this Rag is well marked. At Oxford we have, associated 

 with the Coral growth, a rich underlying shell-bed, and the Wheat- 



