106 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



extended further southward, a waved irregular hue generally sepa- 

 rated these latter from some unfossiliferous pebbly beds above. The 

 upper bed being derived in great part from the destruction of the 

 lower, and the materials being so similar, renders it difficult to 

 discriminate between them either here or anywhere in the immediate 

 district. Viewed, however, on a large scale, this distinction is ap- 

 parent. In conjunction with Mr. De la Condamine I had an exca- 

 vation 10 feet deep made beneath the London clay at the north base 

 of Shooter's Hill, and found that it reposed directly, and without ad- 

 mixture of pebbles, upon the great mass of sandy shingle spread over 

 Plumstead Heath and Blackheath ; just as at New Cross and Lewis- 

 ham it reposes upon an equally compact bed of similar shingle, but 

 which in these localities is only 1 to 2 feet thick. This latter bed I 

 have before shown to extend uninterruptedly w^estward through the 

 London district and as far as the Isle of Wight, maintaining through- 

 out its range a general thickness not exceeding 2 to 5 feet. Although 

 attaining such a remarkable thickness at Blackheath, still as no break 

 or division can be detected in the mass, it may be considered as a 

 development of the same bed, — a view confirmed by a constant cha- 

 racter before shown to attach to the Basement-bed of the London 

 clay, viz. that of reposing upon a worn and eroded surface of the 

 underlying beds. This feature is very marked in the Blackheath 

 district. Great hollows, swept out of the pebbly sands and fossili- 

 ferous clays, are filled up by these masses of shingle beds. In one 

 locality on Blackheath the upper sands of the Woolwich group are 

 25 feet thick and come almost close to the surface, whilst in a pit a 

 few hundred feet N.W. and on the same level the sands are entirely 

 wanting, being replaced by the pebble beds. Very thick agglomera- 

 tion of pebbles, and frequent false stratifications shehing down, 

 generally northward, from 20° to 3.5°, mark these pebble beds, which 

 in some places on Plumstead Heath attain the great thickness of oO 

 to 70 feet. Traces of shells are occasionally met with in them, but 

 they are in so friable a state that it is difficult to determine their 

 characters. The Cardium, Nucula, and Cyrena, all probably the 

 same as the Woolwich species, have been recognised. 



Proceeding eastward from Woolwich the JNIiddle division of the 

 Lower Tertiaries resolves itself more distinctly into — 1st, upper beds 

 of sand with subordinate layers of pebbles, clay, and containing many 

 of the shells found in the pebbly sands of Lee and Woolwich ; 2nd, 

 beds of laminated brown or dark grey clay with Ostrea, Cyrena, 

 Melania, and Cerithium, 6 to 1 feet thick ; and 3rd, lower beds of 

 pebbly light-coloured green sand varying in thickness from 1 to 30 

 feet. 



The upper bed has, however, often been removed by the denudation 

 preceding the deposition of the " Basement-bed of the London clay," 

 — a denudation which has sometimes deeply eroded this middle divi- 

 sion, as shown for instance in the section on the side of the lane 

 leading from the Abbey Wood Station up the Abbey Wood hills, 

 where the Basement-bed of the London clay reposes upon the lower 

 beds of the Woolwich series. The middle bed (fossiliferous clays) 

 exists further back (S.) in the hill and crops out by Wickbam Church. 



