If I can be allowed an OT post, it depends on how well the sand and gravel are consolidated. Chichester, for instance, is on a gravel basin over underlying chalk, but subsidence isn't a worry here.
The sinkhole problem east of Dorchester arises because rain acidified by passage through overlying sand dissolves the underlying chalk; and the same goes for Maidstone except that it's calcareous ragstone, not chalk.
As for clay subsidence, if you drive from Haslemere on Weald clay up to Hindhead on Greensand rock, you can tell the exact boundary by the place where the road no longer shows signs of subsidence.
But just to show that I do read thread titles, indoor temp is 20.3C with windows open.
Originally Posted by: DEW