544 ME. J. CARTER ON THE 



" The clay is of a dark blue colour throughout, and its upper part 

 -contains a considerable quantity of small selenite crystals. The 

 limestone is of greyish colour and very impure, and occurs in the 

 form of nodular bands or regularly bedded ; the beds, however, are 

 not constant. 



" The Oxford Clay is overlain by a bed, 3 feet thick, of brown 

 ferruginous limestone, locally known as the St. Ives rock, now seen 

 •only in a small exposure near the western boundary of the brickyard. 

 There has been some difference of opinion as to the geological 

 horizon to which this limestone belongs. Professor Seeley maintains 

 that it lies about 130 feet down in the Oxford Clay, whilst it is 

 mapped by the Geological Survey as Lower Calcareous Grit ; and 

 further, Messrs. Blake and Hudleston are of opinion that it belongs 

 to some part of the age of the Lower Calcareous Grit, or even 

 higher. I have elsewhere shown (Sedgwick Essay for 1886) that, 

 from a consideration of its fossils, and also on stratigraphical 

 grounds, the St. Ives Rock must be placed on the horizon of the 

 Lower Calcareous Grit. The following fossils, among others, occur 

 in the St. Ives Eock, all of which are characteristic of the Lower 

 Calcareous Grifc of other areas: — Amm. perarmatiis, Modiola hipartita^ 

 Waldheimia hucculenta, W. Hudlestoni, CoUyrites hicordata, 



"Assuming, then, that this is the true positon of the St. Ives Eock, 

 it necessarily follows that the clays in the St. Ives clay-pit which 

 come below it must belong to the uppermost zone of the Oxford 

 Clay ; and this view is supported by the fact that the fossils found 

 in the clay at St. Ives are precisely similar to those which occur in 

 this horizon of the Oxford Clay in other parts of England. 



" Subjoined is a list of the most common fossils from the clay of the 

 St. Ives pit : — 



Alalia tvifida. 



Nucula nuda. 



Leda lacryma. 



CucuUtca concinna. 



Grypha^a dilatata (in abundance). 



Waldheimia impressa. 



Terebratula oxoniensis. 



Acrosalenia, sp. 



Serpula, sp." 



Ammonites athleta. 



cordatus. 



Mariee. 



Lamberti. 



dentatus. 



Eugenii. 



Jason. 



perarmatus (rare). 



Belemnites Puzosianus. 



Most of the Crustacean specimens are more or less mutilated, and 

 eorrespondingly difficult of positive specific determination. In all 

 cases, therefore, when in doubt whether a specimen was identifiable 

 as a described species, I have thought it better to consider it with 

 reference to its allied forms, than to regard it as a new species. 

 Some of the species which I have to mention are indicated by the 

 occurrence of their chelae only. I have had considerable hesitation 

 in deciding how far it was warrantable to regard the occurrence of 

 detached limbs as sufficient evidence of the existence of a distinct 

 form ; but it seems probable that in some genera the carapace was 

 so thin and fragile as scarcely to admit of preservation in a recog- 

 nizable form, and that only the more solid portions of the test, the 



