Summary: (1) Certain portions of the aplite have developed a soda-lithia phase characterized by the presence of petalite, a mineral not previously recorded from the British Isles, and its product of decomposition, montmorillonite.

(2) The Meldon aplite affords a good example of the pneumatolytic phenomena so characteristic of the granites of the West of England.

(3) Evidence is brought forward to show that apatite occurs as a pneumatolytic mineral in the aplite.

I desire to express my most cordial thanks to Dr. E. H Young of Okehampton, who placed his material and knowledge of the district entirely at my disposal for the purposes of this investigation.