Vol. 57.] 



CORALLIAS^ OF ST. IVES AND ELSWORTH. 



iO 



recorded by Prof. Seeley at the bottom of the railway-cutting. 

 At Chettering Parm, near Stretham Pen, Elsworth Rock, associated 

 with a sandstone band, was noted by Roberts in a well-boring. 

 I have recorded Elsworth Rock at Upware, closely associated with 

 the Upware Coral Rag and Oolite.^ 



No surface-exposure of the Elsworth and St. Ives Rock, except 

 at these two localities, seems to be known in the district under 

 consideration ; but Mr. A. C. G. Cameron ^ noticed a rock at Hilton 

 containing Ammonites and Pholadomya. 



As to the mutual relationship of these rocks, Mr. H. B. Woodward * 

 says : 



' The Elsworth Rock was then (1862) considered to be the uppermost zone 

 of the Oxford Clay ; it is now regarded as equivalent to the St. Ives Rock, 

 and both are grouped with the Lower Calcareous Grit, a view suggested by 

 Messrs. Blake & Hudleston, and confirmed by Thomas Roberts,' 



by whom a list of fossils from these rocks was given. ^ 



On the pablished map of the Geological Sarvey the Elsworth 

 Rock is not traced west of Elsworth, and the ' Lower Calcareous 

 Grit ' there I'epresented appears to indicate an assumed higher bed : 

 consequently it does not coincide with the outcrops here to be 

 described. 



II. Outcrops south of the Ouse. 



The grey limestone weathers yellowish-brown, and disintegrates 

 to a yellow calcareous marl with ironshot grains, which often may 

 be easily traced at the surface. There are indications of a very 

 hard blue band, apparently associated with the lower part of the 

 rock, crowded with Serpula and generally full of Exogyra nana : 

 it seems to be persistent as far as Upware, and is like the bed in 

 the floor of the brickyard at Gamlingay. 



About 1^ miles south of Croxton cross-roads, and 200 yards 

 north of Abbotsley Brook, ferruginous and calcareous marl, with 

 fragments of somewhat oolitic limestone, may be found in a ditch 

 by the roadside. There is also a band of hard limestone, whitish 

 when weathered, but bluish-grey when less altered. I found the 

 following fossils : — 



Pleiirotomaria sp. 



Exogyra nana, Sow. (extremely abun- 

 dant). 

 Gryphcea sp. (few fragments). 



Ostrea {Alectryonia) gregaria, Sow. 

 JPecten articulatus (?) Schloth. 

 Vermilia sulcata (?) Sow. (abundant). 

 Serpula gordialis (?) Schloth. 



Although 



the oolitic type of the Elsworth Rock was only 

 represented here by a few fragments in the marl, the hard 

 limestone with Serpula, as also the great abundance of Exogyra nana, 

 and the general assemblage of fossils, so closely recall the lower 

 part of that Rock at Red Hill Farm, Hilton (described on p. 79) 

 and elsewhere, that I have little doubt of its identity. 



^ Quart. Journ. Geol. Soc. vol. liv (1898) p. 601. 



2 Mem. Geol. Surv. ' Jurassic Rocks of Britain ' vol. v (1895) p. 141. 



3 Ibid. p. 139. 



* ' Jurassic Rocks of the Neighbourhood of Cambridge ' 1892, p. 25. 



