_Note._--Conglomerate chalk is, like cob, vulnerable to the attacks of a
really determined rat.
The outer defences provided by the exterior rendering can be backed up
by the mixing in of broken glass or sharp flints with the substance of
the wall, where such attacks are likely.
[Illustration:
+Marsh Court, Hampshire.+]
[Illustration:
+Brick-and-chalk Vaulting at the Deanery Garden, Sonning+]
[Headnote: Block Chalk]