Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/300

 plain of Blackheath, which extends thence eastward to Plumsted Common and Boston Heath. (See map, Pl. 13.)

On the inner edge of this platform at the Plumsted Common brick kilns, which are at the base of the north-east extremity of Shooter's Hill, a large section exposes the London clay, abounding in selenites and septaria. This clay is dug for brick tiles and coarse pottery. In the same field with the clay pits and on the north side of them a shaft is sunk 120 feet to the surface of the subjacent chalk, which has been extracted to the further depth of 24 feet, being the object for which the shaft is made. The upper portion of this shaft is in alluvial gravel, between which and the chalk occur the Woolwich sands. Another shaft was begun in the same fields still nearer to the base of Shooter's Hill, but abandoned from the quantity of water that came in when they were at a depth of which the plastic clay should be found if continued to this point from Woolwich in the same relative position which it there occupies. The same thing happened in an adjoining field, where the shaft for chalk was stopped by the water at the depth of 36 feet.

In a ravine at the east end of Plumsted Common that falls towards the Thames, the plastic clay that upholds the water of these wells and shafts, is laid open on each side of the hollow way, and throws out a line of springs at its junction with an incumbent stratum that is identical with the bed covering the plastic clay at Blackheath and Woolwich. On the east of this ravine in a deeper hollow called the King's Highway we recognise the sand and gravel beds below this plastic clay corresponding with Nos. 4,5,6, of the Woolwich Pit, and 4, 5, 6, of the Loam Pit Hill section; beneath these is the ash coloured sand No. 3 of Woolwich. The King's Highway descends into a still deeper valley (through which runs the road leading from Plumsted to Wickham); this valley is cut to a considerable depth in the chalk.