288 The Rev. W. Buckland on the Plastic Clay Formation. 



A similar section to that at Woolwich and Loam Pit Hill may be 

 traced round the sloping terrace that bounds the north-west and south 

 sides of the plain of Blackheath. 



On the east side the beds composing this plain appear to be covered 

 by the clay of Shooter's Hill, an outlying summit of the London 

 clay, like the hills of Sydenham and Highgate, and which probably 

 at one time were all united in a continuous stratum covering the 

 entire series of the plastic clay formation, which is now exposed 

 between the intervals of its remaining fragments. (See map and 

 section, PI. 13.) 



The plain of Blackheath (being a portion of the strata thus laid 

 open,) is covered at the surface with a bed of rounded pebbles, 

 sometimes 20 feet in thickness, which appear to be alluvial, but are 

 of nearly the same substance with the gravel of the neighbouring 

 strata, from which it is therefore matter of great difficulty to distin- 

 guish them. Beneath these pebbles is a bed of sand identical with 



The Surveyor observed that the foundations of the old church stood upon a layer of 

 very close hard pot earth, which he therefore judged firm enough to support the new 

 building ; and on digging wells in several places he found this pot earth to be about six feet 

 thick and more, on the north side of the church yard, but thinner and thinner towards 

 the south, till it was scarce four feet upon the declivity of the hill. Below this he found 

 nothing but dry sand, mixed sometimes unequally, but loose, so that it would run through 

 the fingers. He went on till he came to water and sand mixed with pcrriwincles and other 

 sea shells; these were about the level of low water mark. He continued boring till he 

 came to natural hard clay. 



The upper stratum of pot earth had been used at a Roman pottery, near the N.E. angle 

 of the present church, where they found urns, sacrificing vessels, and other pottery in 

 great abundance, and were interrupted in digging the foundation of the N.E. angle of 

 the church, by the quarry from which the pot earth had been extracted: the subjacent 

 sand and gravel beds being considered too loose to support the weight of the intended 

 building, it was thought necessary to secure this part of the foundation by erecting it 

 upon an arch. The outer or N.E. pier of this arch stands in the old clay pit, in a shaft 

 sunk to receive it more than 40 feet below the stratum of pot earth that had been removed, 

 and descending through the beds of sand and gravel above mentioned, to the subjacent 

 stratum of hard clay. 



