It has been reported that measurements of the ionization produced by the gamma-rays from Quincy granite are in excess of the ionization computed from the measured uranium, thorium, and potassium content of the rock by a factor of over two. It was concluded that either the measured radioactive contents were much too low or that a hitherto unknown penetrating radiation was given off by the granite.

Measurements of the gamma-radiation from Quincy granite have now been made in such a way that it is unnecessary to compute the ionization arising from the reported radioactive contents in order to make the comparison. After the measurements of the ionization produced by the Quincy granite were made, uranium, thorium, and potassium were added in the form of pitchblende, monazite, and potassium carbonate in amounts which would exactly double the reported radioactive contents. The ratio of the measured ionization in the latter case to that in the former was 2.06±0.13. The gamma-ray ionization from the Quincy granite thus seems to be fully accounted for by the measured uranium, thorium, and potassium content.

Now, when the results of the previously reported measurements of the ionization from the Quincy granite and the present measurements are reduced to comparable conditions, the two sets of measurements are in good agreement; therefore, it seems likely that the discrepancy which had indicated a large excess of penetrating radiation, or a large error in the measurement of the radioactive content, may have arisen in the computation of the expected ionization. This conclusion is fully supported by very recent work on the gamma-radiation from potassium which was reported after the preparation of this paper.

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