The Stability of Lead Isotopes from Thorium

Abstract

PROF. SODDY having given me the privilege of reading his letter in advance, I should like to take the opportunity of directing attention to the geological age of the thorium minerals of Ceylon, and to a few further statistics bearing on the suggestion that only 35 per cent. of thorium produces a stable isotope of lead. I am indebted to my friend, Mr. E. J. Wayland, late assistant mineral surveyor of Ceylon, for the following provisional classification (in order of age) of the older rocks of the island:—