276 A. J. JUKES-BROWNE ON THE RELATIONS OF 



of small oysters, &c. on the fractured surfaces of bones and nodules, 

 he says, " it is possible that Terebratulina gracilis and some others 

 may be of the age of the deposit, and may be found at the base of 

 the Chalk"*. This opinion he will find abundantly confirmed by 

 the lists appended to this paper, and the facts herein recorded. 



§2. Further Analysis of the Fauna. — Although the fossils are only 

 divisible into two groups as far as regards their present mineral 

 condition, it would appear that there are representatives of a third 

 fauna among them ; for though the fossils from the Lower and Upper 

 Gault are in the same state of preservation, the faunas of these two 

 divisions are really very distinct, that of the former answering to the 

 Albien, and that of the latter to the Gault superieur, or Vraconnien 

 of Swiss geologists f . Now although most of the Cambridge fossils, 

 and especially the commoner species, belong clearly to the Upper 

 Gault, yet many characteristic of the Lower also occur, in conse- 

 quence of the extensive denudation which, I believe, the whole 

 Gault formation has undergone over this area. 



We have therefore a strange mixture of forms in this narrow 

 little band of rock ; and the appended list of derived fossils would 

 not, if taken as it is, point definitely to the horizon whence most 

 had been derived, or to the fauna which they may be said to represent. 

 The strong Upper-Gault character of the assemblage ouly comes out 

 when the more abundant forms are taken as a basis of comparison. 

 Our first care therefore must be to separate out those species which 

 are of very rare occurrence, and likewise those which, being* only 

 known in this bed, afford no means of comparison. The first of the 

 following lists contains those which have been cited as new species 

 by Mr. Seeley and others, and have not since been recognized in 

 any other formation ; the second includes the rarer fossils of the bed. 

 Mr. Seeley's species are described in the ' Ann. & Mag. Nat. Hist/ 

 for 1861 and 1865. 



List of Fossils peculiar to the Cambridge Greensand. 



Ammonites glossonotus, Seeley. 



• acanthonotus, Seeley. 



■ sexangulatus, Seeley. 



var. rhamnouotus, Seeley. 



Woodwardi, Seeley. 



■ leptus (var of splendens). 



Pterodonta marginata, Seeley. 



longispira, Seeley. 



Fusus tricostatus, Seeley. 



quinquecostatus, Seeley. 



Pyrula conoidea, Seeley. 

 Funis elongatus, Seeley. 

 brevis, Seeley. 



Pterocera globulata, Seeley. 

 Scalaria angularis, Seeley. 



■ tenuistriata, Seeley. 



Neritopsis scalaris, Seeley. 

 Mesochilostoma striata, Seeley. 

 Pleurotomaria Jukesii, Seeley. 



semiconcava, Seeley. 



Solarium planum, Seeley. 



Carteri, Seeley. 



Sedgwickii, Seeley. 



Littorina crebricostata, Seeley. 

 Trochus cancellatus, Seeley. 

 Turboidea nodosa, Seeley. 

 ' expansa, 



* ' Geol. Magazine,' vol. vi. p. 259, note. 



t That the Gault superieur is rightly so named, and is not equivalent to our 

 English Upper Greensand, I hope to show in a further paper, which is already- 

 advanced towards completion. 



