194 Bibliographical Notices. 



down under locally shifting geographical conditions, so that the 

 district was from time to time divided into ditl'ercnt and changing 

 hydrographical areas, the sediments varying as barriers disappeared 

 or were introduced, and the forms of life more or less readily 

 yielding to the influence of external circumstances." 



Moreover the higher members of the Oolitic group, seen in the 

 south-west, are wanting in East Anglia, either not having reached 

 so far as deposits along the old sea-bottom or having been removed 

 by denudation. 



Particular points in the inquiry carried out by Mr. Roberts were 

 as to the exact geological value of the several bands in the Kimeridge 

 and Oxford Clays, and as to strata representing the Corallian series 

 of neighbouring districts. Here the careful collection and exact 

 determination of the fossils were most important ; and chiefly by 

 means thereof the author came to the conclusion that the Oolites of 

 the district under consideration might be tabulated as follows : — 



Clay I 



1. Kimeridge Clay -It 



Lower. 



{Upware Section. 

 Coral-rag. 

 Coralline Oolite. 



3. Lower Calcareous Grit. (The Elsworth and St.-Ives 



Rocks.) 



4. Oxford Clay. 



This last great formation is here represented by three palaionto- 

 logical zones : — 



1. Zone oi Ammonites perarmatus (rare), A. crenatus, A. omi- 



latus, and the Oordati group of Ammonites of the 

 St.-Ives clay-pit. 



2. Zone of Waldheimia impressa, at the base of the St.-Ives 



clay-pit. 



3. Zone of Ammonites Duncani and A. Jason (the Ornati 



group of Ammonites) of St. jN^eots. [Lowest zone.] 



The valuable, because trustworthy, lists of fossils from the several 

 bands of clay and stone and the full stratigraphical description of 

 other strata, — the careful references to foregoing observations and 

 descriptions, — and the correlation of the Oolites of Cambridgeshire 

 with those of other English districts (pp. 77-86) and with foreign 

 equivalents (pp. 87-94), render this Memoir of very great value to 

 all concerned with the physical geography, the geology, and the 

 palaeontology, of this classic ground and of the corresponding regions 

 in France and Germany. 



