The Rev. W. Buckland on the Plastic Clay Formation. 291 



The north-east side of it is steep, and has at its base a large chalk pit, 

 the top of which displays the Reading oyster bed one foot thick 

 between the chalk and incumbent ash coloured Woolwich sand. 



The plain at the summit of this bank is Boston Heath, where a 

 well has recently been sunk about 200 feet ; through gravel 65 feet, 

 sandy beds 65, chalk 70. The water stands five feet deep in the 

 chalk. I could get no accurate detail of the sinkings, but learnt that 

 in descending they came to water far above the chalk though not in 

 quantity sufficient to supply the well. The upper gravel in this 

 well, and in the shafts at Plumsted, appears to be alluvial, though 

 like that at Blackheath composed almost wholly of pebbles of rolled 

 chalk flints, such as the neighbouring strata of the plastic clay for- 

 mation contain abundantly, and from which they were probably 

 derived. 



The thickness of the alluvium in this district is exceedingly irre- 

 gular, swelling suddenly, and as suddenly disappearing. It covers 

 however nearly the whole surface of the under table land extending 

 from Blackheath to Plumsted Common and Boston Heath, and is 

 found also on the upper table of the summit of Shooter's Hill, as well 

 as on many parts of the slope of its sides. The slopes that fall from 

 the under table to the valley of the Thames are so frequently and so 

 completely covered by this alluvium that except in places where 

 they are laid open by artificial sections, it is difficult to discover the 

 existence of any strata of the plastic clay formation. A striking 

 example of this & t may be seen in the Park, at Greenwich, where 

 nearly all traces of the subjacent beds are concealed by a mass of 

 alluvium along the steep slope where we might expect to see them 

 exposed, and where there can be no doubt of their existence from 

 the strength and regularity in which they appear at Charlton and 

 Woolwich on the east, and near Deptford on the west of Greenwich 

 Park along the continuation of the same escarpment. 



