INTRODUCTION. vii 



Yorkshire shells from those of the West of England, and to have them figured on separate 

 plates, as by this arrangement it is trusted that confusion will be avoided, whatever may 

 ultimately be determined with regard to the position of these deposits. 



It will be observed that several characteristic groups of shells have been arranged 

 into new genera and sub-genera, the knowledge of which, it is believed, will conduce 

 materially to the identification of the members of the lower Oolitic system of rocks ; of 

 these Ceritella, Brachytreraa, Alaria, Cylindrites, and Trochotoma, are likewise represented 

 in the Inferior Oolite, but by other species ; in no instance has any species of these genera 

 been found common to the two formations. Other genera occur whose species are equally 

 characteristic of the two formations ; the table of comparison at the end of the memoir will 

 indeed serve to show how small a number of the spiral univalves are really common to both 

 formations ; with the Patelloidea the case is somewhat different, but the entire number, 

 excluding the Yorkshire species, is very small ; a fact the more worthy of notice as a much 

 larger number of the bivalves are common to both, or if capable of being separated, can 

 only be regarded as sub-species, or varieties of the same species. The literature of the 

 science has hitherto been singularly deficient in illustrations of English Great Oolite 

 univalves ; Lhwyd's ' Lithophylacii Britannici Ichnographia' contains a few ; Conybeare and 

 Phillips, in their ' Geology of England and Wales,' p. 210, enumerate three species. 

 Sowerby's ' Mineral Conchology ' contains thirteen, one only of which is from the Min- 

 chinhampton district. Mr. Lonsdale's paper on the ' Oolitic district of the neighbourhood 

 of Bath' has only three identified species. In Prof. Phillips's ' Geology of Yorkshire,' (part 

 I, p. 128,) fifteen species of univalves are enumerated, which are reproduced in Mr. 

 Williamson's paper on the ' Yorkshire Oolites,' 1 but without descriptions. Dr. Fitton's notice 

 of the strata at Stonesfield 3 gives an accurate enumeration of the different beds, but with few 

 organic remains. In the paper by Capt. L. L, B. Ibbetson and Mr. Morris, on the 

 'Geology of Stamford,' 3 a few univalves are mentioned ; and, lastly, in the ' Geology of Chel- 

 tenham,' edited by Messrs. Strickland and Buckman, a list is given from the Stonesfield 

 slate of East Gloucestershire of six Echinodermata. or at least fragments of them, and 

 nineteen gasteropoda, remains of which, however, are sometimes very imperfect. 4 It may be 



1 Geol. Trans., 2d Ser., vol. v, Part i, p. 240. 2 Zool. Journal, vol. hi. 



3 Brit. Assoc. Reports, 1847. 



4 The following is a section of the quarry on Sevenhampton Common, whence most of the fossils were 

 obtained : 



Soil . . . . . . .2 feet. 



A yellow clay, of a somewhat soapy feel, very rich in fossil shells . 6 ,, 



Ragstone, similar to the Stonesfield slate . . . — ,, 4 inches. 



Thin seam of soft stone, with Ostrea acuminata, and small joints of 



Apiocrinites . . . . , 3 



Blue marl ... 8 



Ragstone . . . . , ,14 

 Stonesfield slate . . 4 



Fullers-earth ... 



