THE CORALLIAN ROCKS OF ENGLAND. 313 



As we indicated at the commencement, it is not our object in this 

 paper to correlate the various deposits described with what may be 

 their representative portions of the argillaceous series ; but, for the 

 sake of indicating the possibility of such a correlation, we may record 

 the fact that at Ampthill, the place after which Mr. Seeley has 

 called the middle division of the clay, we have found in the debris 

 of the railway- cutting a well-marked spine of that most characte- 

 ristic Corallian fossil Cidaris jlorigemma, associated with Ammonites 

 plicatilis, Ostrea gregaria, and Serpula intestinalis. 



We do not propose either to enter into a complete discussion of 

 the " Els worth Rock " of the same geologist, although we think that 

 it belongs to some portion of the time during which, elsewhere, 

 Corallian rocks were being formed, and should probably be referred 

 to a position analogous to that of the Lower Calcareous Grit. Thus 

 much appears likely from the character of the fossils in the rich 

 collection in the Woodwardian Museum, among which we may note 

 the following — Ammonites vertebralis, A. goliathus, A. convolutus, 

 A. perarmatus, Pleurotomaria Miinsteri, Astarte ovata, Cucullcea cla- 

 ihrata, Lima elliptica, Avicula ovalis, Millericrinus echinatus, and 

 many others pointing to a lower horizon. As we are promised a 

 description of the whole by their discoverer, and the mass of rock 

 is so isolated amidst the clays as to render its correlation greatly 

 dependent on them, we must pass over any further discussion. 



The same may be said of the Red Rock of St. Ives, which imme- 

 diately overlies the fossiliferous Oxford Clay. This slightly exposed 

 band has yielded several fossils, of which the following have been 

 recognized — Ammonites cordatus, Pleurotomaria Milnsteri, Pecten 

 lens, P. subtextorius, P. Jibrosus, Ostrea gregaria,Waldheimia Hudle- 

 stoni, Pseudodiadema versipora, Collyrites bicordatus, and (!) Cidaris 

 Jlorigemma. 



These seem to indicate that it belongs to some part of the age of 

 the Lower Calcareous Grit, or even higher. 



IY. The Cambridge Reef. 



The well-known though very inaccessible exposure of Corallian 

 beds at Upware, between Cambridge and Ely, demands a more 

 careful description. It has been partially, but not very fully de- 

 scribed by Mr. Bonney in his ' Geology of Cambridgeshire,' in which 

 he correlates it with the lowest portion of the Corallian region, on 

 account of its containing Cidaris Jlorigemma — a reason which would 

 make us assign it to nearly the highest. It has always been called 

 Coral Rag, except by Mr. Seeley, who denominates it " Upware 

 Limestone "*, and places it in the series above the clay equivalent 

 of the Coral Rag. After a comparison of it with the Coral Rag of 

 other areas, its age and nature are left in no doubt whatever. 



The position of the Corallian beds is well known ; they form the 

 basis on which lie the phosphatic nodules and Neocomian sands. 



There are two distinct openings in which the rocks may be well 



* Index to the Fossil Remains of Aves, Ornithosauria, and Reptilia. 1869. 



