THE 'derived' fossils. 35 



On certain Boulders of Neocomian Grits which occur in the East 



of England. 



Some clue to the origin of the dark fossiliferous grits which we 

 have just been considering, may, I believe, be obtained by studying 

 the boulders of green grit which have been found in various locali- 

 ties on the surface in the gravels of the east of England. So long 

 ago as 1812 this rock was made known in the description of Tere- 

 hratula ovoides by Mr J. Sow^erby from ''blocks of sandstone con- 

 taining greensand" (Mineral Gonchology, Vol. I., p. 227, pi. 

 100), found in "some parts of Suffolk." I have found the same 

 rock-boulders containing abundantl}^ the same fossils at South 

 Willingham, in Lincolnshire, and near the inn at West Dereham, 

 Downham Market, Norfolk. The last-named block yielded, besides 

 the Terehratida ovoides (Sby.) a Lucina and Pecten orbicularis (Sby.). 

 Mr Teall in his Essay (pp. 22, 23) cites other localities, namely, at 

 Southery, and in a pit at Hilgay, Norfolk, where he found several 

 such blocks of sandstone with the fossils "Panopcea Neocomiensis, 

 Pecten orbicularis, and Terebratula depressa." And Mr E. Ray 

 Lankester also mentions a gravel-pit at Thorpe, Suffolk, another at 

 Snape, and the Drift at Stow Bardolph. 



I have lately found that several large boulders around Cam- 

 bridge belong to the same set. The great corner-stone by the side 

 of a cottage close by the Coton public-house contains good speci- 

 mens of Pecten orbicularis and Belemnites subquadr-atus, some of 

 the latter very large ; and from other boulders in the farm next to 

 the rectory at Hardwick I obtained Pecten orbicularis and Pinna. 



But the most important of these boulders (as I believe it to be), 

 was dredged up from the bed of the Cam some few years ago at a 

 place called Herrimere between Upware and Ely, where it was 

 found by Professor Seeley and Mr Earwaker, and described by Mr 

 E. Ray Lankester in his paper on "A new large Terebratula occur- 

 ring in E. Anglia," in the Geological Magazine for May, 1870, 

 p. 410. In this paper we are told that the matrix is ''a fine sand- 

 stone conglomerate, closely resembling the matrix from Thorpe and 

 Snape, and having small black pebbles scattered through it." 



The specimens are in the Woodwardian Museum. It is a 

 curious grey sandstone, full of fossils, and the contained pebbles are 

 Lydian stones and rolled phosphatic fragments which have been 



3—2 



