The general application of data from the studies of the rates of disintegration of radioactive elements to the dating of geologic history has been presented comprehensively in Bulletin No. 80 of the National Research Council.1

The present paper reports results obtained from the first detailed application of the helium method to a suite of rocks taken at widely distributed points within a single horizon. These results fully justify Arthur Holmes’ optimistic outlook for the helium method as a means of building up a time-scale which, because of the availability of material, should become far more detailed than any which the lead method alone might yield. Moreover, we now have a method of correlating flows, sills, and dikes without recourse to individual radioactive minerals so often absent from formations of interest. Results for other horizons have been obtained but are withheld the better to coordinate later.


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