GEOLOGY 



They are quite unwaterworn, and appear to have lived on the spot 

 attached to the pebbles which form part of the gravel. 



They all belong to the group of Calci sponges, that is to sponges 

 whose skeleton spicules are formed of carbonate of lime. 



Calci sponges are rare fossils in any case, and it is most unusual to 

 find them as here with no admixture of sponges whose spicules are 

 siliceous. 



About seventeen species occur, the commonest of which, Rapbi- 

 donema faringdonensis, is locally known as the petrified salt cellar. 1 



Pebbles of quartz and other rocks are fairly abundant, and amongst 

 them are many fossils derived from oolitic formations. Thus the Kime- 

 ridge Clay has furnished Exogyra, Ostrea, Perna and Belemnites. There 

 are Cidaris, Diadema, Exogyra and Pecten from the Corallian, and 

 Grypbcea, Belemnites and Ammonites from the Oxford Clay, showing 

 that all these formations were undergoing much denudation during the 

 deposit of the Lower Greensand. 



Owing to the unconformable overlap of this formation the sponge 

 gravel rests partly on Kimeridge Clay and partly on Corallian beds. 

 Possibly it thins out to the south-east. 



Mr. Austen remarks 2 that 'apart from the organic remains [this gravel] 

 might be taken for a mass of stratified drift, a geologist who should be 

 guided by such characters as those of general aspect, mineral composi- 

 tion and mode of accumulation, and who, finding himself in one of these 

 pits was required to determine the age of the deposit, might most 

 excusably suppose himself to be in the Crag district of Suffolk : in both 

 accumulations there is a like condition of the mineral materials, a like 

 arrangement of the component beds, and a like proportion, as well as 

 condition, of the included animal remains. In these latter respects the 

 Faringdon Beds are of great interest as they present to us the only 

 instance now remaining in any part of Great Britain of a bank of sub- 

 angular sea gravel of the secondary period.' s 



The red gravel which rests on top of the sponge gravel at Little 

 Coxwell consists of ferruginous sands and pebbles with beds of hard con- 

 glomerate with Terebratula, bryozoa, etc., but with few sponges. Its 

 thickness is about 20 feet. 



The highest division of sands, with ironstone and some chert, about 

 30 feet in thickness, occupies the upper part of Furze Hill, etc., and 

 the ironstone has been worked in former times. These old workings 

 are known as Coles' pits, and one of them is, according to local tradition, 

 the site of the castle of King Cole. 4 Like the underlying beds the bands 

 of iron ore contain marine shells such as Leda, and this is of some 



1 See G. J. Hinde and H. B. Woodward, Proc. Geol. Assoc. (1891-2), xii. 327, and references 

 given at p. 333 ; see also E. C. Davey, Papers contributed to the second volume of transactions of the 

 Newbury District Field Club (Wantage, 1874). 



2 Loc. cit. p. 454. 



3 On November 7, 1 809, Mr. James Sowerby gave a short account of this gravel to the Linnxan 

 Society (Trans. Linn. Sac. x. 405). 



4 Davey, op. cit. p. 17. 



I 9 "2 



