16 Geolcgy. 



Sand with shells and few pebbles (base not seen), 3 feet. 



This section, which showed very clearly the rapid lateral varia- 

 tion of the Blackheath Beds, as regards composition and thickness 

 of individual layers, yielded a vast number of fish-teeth (Odontaspis 

 elegans) at least 5,000 having been obtained by one collector (10). 

 The upper shell-bed showed in horizontal section as a succession of 

 shelly ridges alternating with troughs filled with pebbles, a structure 

 apparently due to irregular decalcification of the shell-bed and the 

 descent of the pebble-bed into the hollows left by removal of the 

 shelly material. The summits and sides of the ridges were outlined 

 by layers of crushed shells arranged parallel to the slope of each ridge 

 by the pressure of the descending pebbles. It is, however, possible 

 even probable, that some of the ridges and furrows are due to sub- 

 aerial erosion and stream-action. 



On Plumstead Common a huge block of Blackheath conglomerate 

 (locally known as Plum-pudding Rock ) stands on the slope of 

 an old gravel -pit which has been converted into a shrubbery. 

 Calcareous conglomerates, crowded with shells, occur at Charlton, 

 but the Plumstead Common specimen is remarkable for its size. 

 No shells have been noticed in it. 



London Clay. 



The London Clay forms the mass of Shooter's Hill (rising therein 

 to a height of 400 feet above O.D.) covers several square miles 

 south of Eltham and Lee, and appears also in scattered outliers 

 varying from a square mile or more in area down to a few square 

 yards. The London Clay rests always on Blackheath Beds, yet the 

 actual junction is seldom clearly shown in section. It has recently 

 been seen in some small excavations near Eltham Park, and it may 

 be detected in the deep railway-cutting made for the Bexley Heath 

 branch of the S.E.R. 



Although the slopes of the cutting are now nearly overgrown, the 

 junction is plainly marked by a line of little cones of yellow sand 

 thrown out immediately below the London Clay by small burrowing 

 animals. The following section of the junction was noted in an 

 adjacent brickfield north of the railway, in April, 1906 : 



/Brown clay, 3J feet. 



London Clay - Green clayey sand with a few pebbles, 2 J feet. 

 ( Small pebbles very closely packed, 1J feet. 



Blackheath Beds f Thinl y- b edded sand and clay, 2 feet. 

 18 (Fine white sand, 1 foot. 



(10) J. L. Foucar, Tran. W. Kent Nat. Hist. Soc., 1906. 



