Note 35 — Chapter II · PHYSICAL HISTORY OF CAVES.

I have used the term incretionary as implying an accumulation of mineral matter from the circumference of a cavity towards its centre, as in the case of an agate. Concretionary action, with which it is generally confused, ought to be defined as the deposition of successive layers of matter round a nucleus or centre. The one action operates from the circumference to the centre, the other from the centre to the circumference.