Age Determination of Carboniferous Basic Rocks of Shropshire and Colonsay

Abstract

The helium method of determining the ages of fine-grained basic igneous rocks has now been so far developed as to be applicable to various geological and petrological problems, particularly where geological periods are involved, as in the problem here discussed. For details of the history of this development up to the beginning of 1937 reference may be made to Holmes, 1931; Urry, 1933; Lane and Urry, 1935; Urry, 1936 (b); Holmes and Paneth, 1936; and Holmes, 1937. During 1937 it was found that many of the helium-ratios on which the ‘helium’ time-scale had been based were too high, because of a previously unsuspected error in radium determination due to reliance having being placed on a radium standard which was seriously at fault. To clear up this embarrassing situation an immediate effort was made by several investigators in collaboration, and the first fruits of their work have recently become available (Evans, Goodman, Keevil, Lane, and Urry, 1939).