14 Geology. 



villages pass over a broader outcrop the}^ become deep, shady lanes, 

 very delightful in summer and affording a welcome relief from the 

 open tracks on the heaths above. 



Woolwich Beds. 



Sir J. Prestwich adopted the name Woolwich and Reading 

 Beds for the middle member of the Lower London Tertiaries, 

 including under this term two types of contemporaneous sediments 

 Beds of the true Reading type do not occur within our limits ; the 

 Woolwich Beds, characterised by loams and fossiliferous clays 

 are, as the name indicates, here well developed. 



Within our area the Woolwich Beds always rest on Thanet Sand 

 of fair thickness (40 fee tor more). At the base a layer of small flint 

 pebbles is generally present, as at Charlton, Erith, and Wickham 

 Lane. In this last locality, where the pebbles are thinly scattered 

 and splashed into the Thanet Sand, the base can be traced along 

 fully 400 yards of section (9). 



Above the pebbles lies a greenish loam, coloured by glauconitic 

 matter, and often containing ferruginous concretions. The loams, 

 sands, shelly clays, and thinly-bedded clays and sands of the upper 

 Woolwich Beds are all admirably shown in the fine section near the 

 Woolwich Cemetery. (See General Sections}. 



Besides the well-known sections at Charlton and Erith, good 

 exposures occur at the N.E. corner of Plumstead Common, and in 

 the Wickham Lane Brickfields. In all these the shelly clays are 

 found, but notably at Charlton. A small roadside-section at Knee 

 Hill shows the green loam resting on an unusually irregular surface 

 of Thanet Sand. 



Full lists of the fossils of the Woolwich Beds are given in the 

 " Geology of London," Vol. i. 



Blackheath Beds. 



In our district this term denotes the sandy and pebbly beds 

 lying between the Woolwich Beds and the London Clay. Before 

 the deposition of the Blackheath Beds the Woolwich loams and 

 clays suffered unequal erosion, by which troughs were scooped 

 almost, if not quite, through the whole thickness of the Woolwich 

 Beds. It thus comes about that the Blackheath Beds are found 

 resting on any and every part of the Woolwich Series from the 

 green loams up to the laminated clays. A very striking instance of 

 this troaghing may be seen in the sand-pit on Plumstead Common, 

 opposite the Woolwich Cemetery. Here the Blackheath pebble- 



(9) Proc. Geol. Assoc., Vol. XIX., pt. 6, p. 346. 



