360 MR. W. G. FEARNSIDES ON" UPPER GAULT [Aug. I9O4, 



25. On the Occurrence of a Limestone ivith Upper Gault Fossils 

 at Barnwell, near Cambridge. By "William George Fearn- 

 sides, Esq., M.A., F.G.S. (Read May 25th, 1904.) 



In the course of a recent examination of the great Gault-pit worked 

 by the Cambridge Brick Company, Ltd., at Barnwell, my atten- 

 tion was drawn to an unusual and inconstant hard bed which is 

 occasionally met with in the lowest part of the pit. 



On examination, the hard material was found to consist largely 

 of comminuted Inoceramus-fragmeiits, with occasional ammonites 

 and other shells, and a careful search in this and the adjoining 

 clay proved them to be quite fossiliferous. Unfortunately, the 

 specimens obtained are only fragmentarj-, but as they seem to 

 indicate a horizon higher than any yet recorded from the Cam- 

 bridgeshire Gault, 1 they may perhaps be worthy of record. 



The section now seen is as follows, in descending order : — 



Thick ne*> 

 in feet. 



(1) Surface-soil, with gravel and Chalk-Marl, disturbed in the former 1 -.r i - 



working of the Cambridge Crreensand. J ' 



(2) Dull leaden-grey clay, which on drying becomes more creamy ) 



and Aery pale. This is generally almost devoid of determin- | 

 able fossils except Plicotula, but contains a few scattered )- 39 

 phosphate -nodules, marcasite-concretions, and pieces of car- j 

 bonized wood. J 



(3) Compact, well-jointed, homogeneous clay of a distinct bluish ^ 



colour, containing large but undeterminable ammonites of 



the rostratus- or Bouchardianiis-type; also occasional sharks' 

 teeth and lamellibranch-shells. 



(4) The Hard Band, with numerous specimens of Inoceramus, j 



Schlitnbaclda varicosa, Terebratula biplicata, sharks' teeth, V to 1 

 and many phosphate-nodules. 



(5) Very blue, well-laminated clay, with abundant fragments of 1 . 



fossils and many pale phosphate-nodules. J 



Of these, the three lowest divisions are the most interesting, and 

 nearly all the fossils come from the beds (4) and (5). The Hard 

 Band (4) is extremely variable in thickness. It occurs in a series of 

 flattened lenticles, generally a few yards in diameter and up to a 

 foot in thickness. It is largely made up of broken shells and 

 phosphate-nodules, with a few bone-fragments and extraneous 

 pebbles of mud, and is harsh to the touch. Some of the ammonites 

 and Inocerami are very large, and specimens of the latter 3, 4, and 

 even 5 inches across are not uncommon. 



Petrologically, the Hard Band is best described as a somewhat 

 muddy shell-limestone. It contains abundant phosphate-nodules, 



1 See Mem. Geol. Surv. 'The Cretaceous Rocks of Britain, vol. i (1900) 

 The Gault & Upper Greensand of England ' p. 287. 



