68 //. A. Baker — Quartzite Pebbles of tJte OldJiaven Beds. 



Ostrea hellovacina in the Woolwich Series to be encountered in a 

 sihcified condition. This has been well seen in borings at Woolwich 

 Arsenal, and also at Well Hall, near Eltham. The cementation of 

 this bed is, however, frequently ferruginous in character. The same 

 is true of the indurated masses so often seen in the Blackheath 

 Pebble Beds of this district. At the large brick-iDit at South Bromley 

 patches of flint-j)ebbles cemented in a siliceous matrix have been 

 seen in pebble-beds separated from the London Clay above by about 

 20 feet of sands, clays, and pebble-beds,' but it appears to be much 

 more usual to find that where the Blackheath Pebble Beds are locally 

 cemented into conglomerate, the cement is largely ferruginous in 

 character. Such was the case, for instance, at the Kidbrooke 

 Tunnel.^ On Plumstead Common, near the bandstand, is a large 

 mass of Blackheath Pebble Beds (an outcast mass from some very 

 old gravel-pits, now vanished) firmly cemented into a hard pudding- 

 stone by a cement which is apparently more ferruginous than 

 siliceous. 



On the Continent, in Belgium, and North France, sarsen-stones 

 are of common occurrence in the beds equivalent to our Woolwich 

 and Reading Series. Mr. L. D. Stamjo, who has recently familiarized 

 himself with the Eocene sequence in these areas, informs the writer 

 that the occurrence of sarsen-stones in the fluviatile facies of the 

 Upper Landenian of Belgium and the Sj)arnacian of the Paris Basin 

 is a characteristic feature. 



At the present time it appears that results afforded by inquiry 

 along three independent lines now point to a common conclusion. 

 In the first place, as the result of the search for evidence concerning 

 the origin of the sarsen-stones, it may now be taken as satisfactorily 

 established that the Woolwich and Reading Beds have afforded 

 one source of supply. Secondly, study of the petrology of the sarsen- 

 stones has revealed a close affinity between them and the material 

 of the Woolwich and Reading Beds. This question has been 

 investigated by Professor P. G. H. Boswell,^ who found the mineral 

 suite of the sarsen-stones to be precisely similar to that of the 

 Reading Beds, and who concluded that the distribution, mineral 

 constitution, and general characters of the sarsens indicates their 

 probable derivation from the sands of the Reading Beds. Thirdly, 

 as indicated above, the mineral suite of the quartzite-pebbles of 

 the Oldhaven Beds points to a close affinity between them and the 

 sands of the Woolwich and Reading Beds. All that now appears 

 to be required is some definite piece of evidence indicating a direct 

 connexion of the sarsen-stones with the Oldhaven quartzites, and 

 a recent fortunate find of the writer's apparently affords the necessary 

 connecting-link. The photograph shown in the Plate (Fig. 1) is 

 of a rolled quartzite-pebble which the writer obtained in situ in 



1 Summary of Progress Geol. Surv., 1913, p. 29. 



2 T. V. Holmes, Proc. Geol. Assoc., vol. viii, 1893-4, p. 154. 



' Boswell, Quart. Journ. Geol. Soc, voL Ixxi, 1915, pp. 573-4. 



