70 H. A. Baker — Quartzite Febhles of the Oldhaven Beds. 



were deposited, in no great length of time, to form the Blackheath 

 Pebble Beds. 



From this point of view we may regard the occurrence of these 

 rolled quartzite-pebbles in the Blackheath Beds as additional 

 evidence of the pre-Oldhaven erosion of the Woolwich and Beading 

 Beds. 



It is somewhat singular that Prestwich, in the classical series of 

 papers on the strata between the London Clay and the Chalk, 

 appears never to have suggested the possibility of these quartzite- 

 pebbles of the pebble beds being rolled fragments of sarsen-stone. 

 He knew of their occurrence in the pebble-beds, for he stated that 

 he had occasionally found them in situ, and suggested that the 

 similar pebbles of the Westleton Beds may have been derived from 

 the Lower London Tertiaries. He pointed out their difference 

 from the quartzites of the Triassic conglomerates, but suggested 

 the jDossibility of their having been derived from the Palseozoic 

 quartzites of the Ardennes. The point is the more remarkable 

 inasmuch as Prestwich, in amassing strong evidence in favour of the 

 Woolwich and Reading Beds having been one (and possibly the 

 chief) source of supply of the sarsens and puddingstones, was at 

 pains to emphasize the fact that the pebble beds overlying the 

 Woolwich and Reading Series rest upon a strongly eroded surface 

 of the latter beds, and are themselves derived in great part from the 

 destruction of the lower beds. 



Summarizing, in conclusion, the main points put forward in the 

 present communication, the writer contends that without attempting 

 to dogmatize upon the question of the scope and applicability of 

 the term " sarsen ", but employing it in the general sense now 

 permitted by usage, as free from the limitations some would impose, 

 the following points may now be regarded as established : — 



(1) The sarsen-stones and puddingstones considered here are 

 cemented portions of sandy and pebbly Lower Eocene strata. 



(2) The Woolwich and Reading Beds have afforded one source 

 of supply of these stones. 



(3) The pebbles of quartzite and siliceous flint-conglomerate 

 occurring in the Oldhaven (Blackheath) Beds are rolled fragments 

 of sarsen and puddingstone derived from the Woolwich and Reading 

 Beds. 



EXPLANATION OF PLATE I. 



Fig. 1. — Rolled quartzite pebble from the Oldhaven (Blackheath) Pebble Beds. 

 Road cutting east of Plumstead Common. Four-sevenths full size. The 

 quartzite contains rolled pebbles and broken fragments of black flint. Note 

 flint pebble f in. long showing on surface of quartzite at left-hand end of 

 photograph. The quartzite also contains rolled pebbles of white quartz. 



Fig. 2.-— Section of pebble shown in Fig. 1, showing flint. Ordinary light. 

 Magnified six diameters. 



Fig. 3. — Section of pebble shown in Fig. 1, showing flint ; quartz-grains rather 

 closely packed, not much cement. Crossed nicols. Magnified eighteen 

 diameters. 



