No. 12 at Loam Pit Hill. This sand lies on a bed of plastic clay which supports the water of the well in Mr. Conybeare's garden, and of all the wells on the plain of Blackheath at no great depth; it possesses the same peculiar dark red colour, with the plastic clay of Reading, Corfe Castle, and Paris, and has been used for pottery.[1] Beneath this clay the Woolwich shell beds and subjacent thick ash coloured sand are to be seen in several parts of the sloping terrace that surrounds the Blackheath plain. Under these on the north and west sides appears the chalk, separated from the ash coloured sand by the same thin pebble bed as at Reading. This pebble bed not attaining the thickness of one foot may be seen at the junction displayed by the descent to some ancient subterraneous quarries in chalk, called the caves, on the north side of the road ascending to Blackheath from Deptford; it may be seen also on the south side of the same road in some chalk pits on the slope of the hill: in both places it is covered by the thick ash coloured sand.
In the lane that leads down from the village of Charlton to the Thames, is a good section shewing the Woolwich shell beds incumbent on the ash coloured sand which appears there in great thickness.
The church of Charlton is on the edge of the continuation of the
- ↑ It is probable that the plastic clay contains at Blackheath as at Corfe Castle, Alum Bay and Loam Pit Hill, the remains of vegetable matter in a state approaching to coal; and that this circumstance has given origin to the erroneous opinion so prevalent, that
there is good coal at Blackheath if Government would allow it to be worked.
The very high improbability of finding good coal above the chalk is acknowledged by all who have even the smallest acquaintance with the geological relations of the English coal mines. The presence of black vegetable matter in a state approaching charcoal in almost all our secondary argillaceous strata, has caused endless vain attempts to search for useful coal in formations where the discovery of that substance would be contrary to all experience in this country. No good coal has I believe been yet found in England in any stratum more recent than the new red sandstone, or red rock marl. That of the Cleveland Moors in Yorkshire, being above lias and in the oolitc formation, is of so bad a quality as scarcely to form an exception to this position.
