98 ppvof. j. peestwich on the coeeela.tion oe the 



Woolwich and Eeadtng Beds. 



I have shown in former papers * that the non-fossiliferous clays 

 and sands of Eeading pass, as they approach London, into pebbly 

 sands ; and, as the mottled-clay element gradually disappears, these 

 sand- and pebble-beds become fossihferous. At the same time an 

 intercalated zone of fluviatile clays and thin lignites sets in in the 

 middle of the series, attaining considerable importance immediately 

 east of London, and extending nearly to Paversham. There these 

 fluviatile beds, which at Woolwich divide the pebbly marine and 

 estuarine sands into two groups, thin out, and the upper and lower 

 sands inosculate, so that at Heme Bay all traces of the freshwater 

 element are lost, unless it be represented by the few fragments of 

 drifted wood, and none but marine fossils remain. 



These fuller marine conditions bring in at the same time other 

 fossils wanting in the London district, which serve to connect this zone 

 with the Bracheux Beds, such as Cy]prina Scutellaria and Cucullcea 

 crassatina. But these would hardly be sufficient to establish the 

 contemporaneity of the two deposits were it not for other general 

 conditions and the help of certain negative evidence. 



The characteristic shells of the Thanet Sands — Pholadomya 

 Koninckii, P. cuneata, Panopcea granulata, and Scalaria BowerhanJcii 

 — are wanting in the glauconiferous sands representing the "Woolwich 

 Beds in East Kent; while such characteristic Woolwich shells as 

 Ostrea hellovacina, Pectunculus terehratularis, Pseucloliva Jissurata, 

 and Cardium semigranulatum, are wanting in the underlying Thanet 

 Sands. 



A shell which, though not found at Bracheux, is common in the 

 equivalent beds at Gannes a few miles distant, was also found a 

 short time since in the Woolwich Beds in the fine section exposed 

 near Croydon in making the railway- cutting on the Oxted line. 

 This is a Perna which seems to be Perna Bazini, a shell of very 

 definite form and of limited range. 



Another character of secondary importance, but which, from its 

 bearing on the origin of the strata, becomes of consequence, is the 

 mineral composition of this series. In the Paris Basin the strata con- 

 sist essentially of light-coloured quartzose and glauconiferous sands, 

 mixed, when in the proximity of the fluviatile beds, with large 

 quantities of flint pebbles, and elsewhere passing into red and 

 mottled unfossiliferous plastic clays. Further, while a peculiar 

 condition of the sands is presented by the Sarsens and Pudding- 

 stones of the London Basin, blocks of hard sandstones (passing into 

 quartzites), together with extensive pebble-beds (associated in places 

 with fluviatile beds and lignites), extend in France irregularly over 

 the plains of Picardy, passing southward into mottled clays and 

 northward into the Upper Landenian, in which organic remains are, 

 as a rule, extremely scarce. M. Gosselet, however, records the occur- 

 rence of Pectunculus terebratidaris in these beds (to the south of Lille), 

 which he terms the Sands of Ostricourt. He also notices the common 



* Quart. Journ. Geol. See. vol. x. pp. 75-170. 



