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and ductile. If dry, it adheres more or less tothe tongue: if thrown into water, it graduallydiffuses itself through it, and slowly separatesfrom it. It does not usually effervesce withacids, unless a strong heat be applied, or thatit contains a few calcareous particles, or mag-nesia. If heated, it hardens and bums to abrick.

It consists of argill and fine sand, usually ofthe silicious kind, in various proportions, andmore or less ferruginous. The argill formsgenerally from 20 to 75 per cwt. of the wholemass; the sand and calx of iron the remainder.These are perfectly separable by boiling instrong vitriolic acid.

Chalk, if not very impure, is of a white co-lour, moderate consistence, and dusty surface,stains the fingers, adheres slightly to the tongue,does not harden when heated, but, on the con-trary, in a strong heat burns to lime, and losesabout four-tenths of its weight. It effervesceswith acids, and dissolves almost entirely therein.I shall also add, that this solution is not dis-turbed by caustic volatile alkali, as this circum-B 4