Vol. 57.] 



OF ST. IVES AND ELSWOSXH. 



79 



ferruginous limestone in a yellowish soil. A few yards east of the 

 outcrop black laminated Ampthill Clay was seen in a pond. To 

 the north Eed Hill Farm stands on a ridge running roughly 

 north-eastward and south-westward. Here is the rock noted by 

 Mr. Cameron/ as mentioned on p. 75. I found it well exposed on 

 the southern slope in a trench. It is a very hard bluish-grey lime- 

 stone, with some calcite, full of Serpula and Exogyra, underlying a 

 yellow marly soil which contains many lumps of ferruginous lime- 

 stone and oolitic ironstone. I obtained : — 



Ammonites (Perisphi?ictes) plicatilis, 



Sow. 

 A. {Cay^dioceras) cordatus, Sow. 

 Exogyra nana, Sow. (yery abundant). 



GryphcBci sp, (abundant), 

 Ostrea {Alectryonia) gregaria, Sow, 

 Pecteoi articulaius (?) Scblotli. 

 Serpula (abundant). 



Immediately south of the ridge is a pond, apparently in Oxford 

 Clay, in which Gryphcea and pyritized ammonites occur. On the 

 top of the ridge, and on its northern flank, the Els worth Hock is 

 again recognized. On revisiting this locality I had the advantage 

 of Mr. Keeping's company. He pointed out the close resemblance of 

 the hard limestone to the band in the floor of the pit at Gamlingay, 

 as well as to the lower part of the rock at Elsworth. 



The outcrop probably does but cross this ridge, on the eastern 

 part of which it seems to have passed under dark Ampthill Clay 

 containing much selenite. It certainly has an easterly dip here, 

 Conington, where Prof. Seeley records a rock-bed at a depth of 

 100 feet, is about a mile to the east. There can (I think) now be 

 little doubt that this is the Elsworth Eock, a conclusion which also 

 applies to the rock-bed seen in wells at Papworth Everard. 



Beyond E-ed Hill Farm nothing is seen for a considerable distance : 

 the outcrop of the Rock would naturally turn eastward on reaching 

 the Ouse Valley. It is certainly absent on the east side of Fen- 

 stanton, where at the Brewery a boring has lately been made to a 

 depth of nearly 200 feet. By the kindness of Mr. Burt, of Fenstantou, 

 I was able to examine the material. No Eock was met with, and 



I obtained the following fossils : — - 



Avicida inaquivalvis, Sow. 



Gryphaa hilobata, Sow. 



Gr. dilatata, Sow. (abundant). 



Feet en sp, 



BhyncTionella varians, Schloth. 



the clay is certainly Oxford Clay. 



Ammonites (Pelioceras) athleta (?) Phill. 

 A. {Cardioceras) cordatus, Sow. (abun- 

 dant). 

 A. {C.) Maria (?) d'Orb. 

 A. (C.) excauattcs (?) Sow. 

 Alaria trifida, Phill. 



It has been mentioned (p. 73) that Thomas Eoberts noticed a 

 brown rock not far from the surface atSwavesey. 



About 1100 yards west of the Castle Hill, Swavesey, in material 

 dug from the drain, I found yellow marl containing several 

 small fragments of yellow ferruginous limestone with Sey-pula, and 

 have little doubt that the Elsworth Eock crops out here, approxi- 

 mately where it might be expected to do so. 



^ Mem. Geol. Surr. ' Jurassic Eocks of Britain ' vol. y (1895) p. 141. 



