°" American Journal of Science, vol. 23, 1907, p. 87. 

 "1 American Journal of Science, vol. 28, 1884, p. 431. 



"- Hidden & Jlackintosh : American Journal of Science, vol. 38, 1880, p. 474. 

 Ilillebrand : American Journal of Science, vol. 46, 1893, p. 99, and vol. 13, 1902, 

 p. 145. 



■^Die Mineralien der Syenitpegmatitgange, part I, pp. 160, 164, and part II, p. 10. 



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134 G. r. BECKER RELATIONS OF RADIOACTIVITY TO COSMOGONY 



Mr Boltwood "" has computed the age of a large number of uranium 

 minerals from their lead content. He shows that according to theory 

 the age will be given in years to a first approximation, if the ratio of 

 metallic lead to metallic uranium is multiplied by 10 million. In this 

 way he gets for the age of the Glastonbury mitierals 410 million years. 

 Xow, at Barringer hill, in Llano county, Texas, there is a very remark- 

 able deposit of rare radioactive minerals, which are so abundant that 

 they have been mined for the use of an electric lighting company. It 

 happens that the age of the granite in which the pegmatite occurs is 

 known. Mr Walcott " discovered in this county his Llano group, which 

 belongs to the Grand Canon series not far below the Cambrian. The 

 granites are intrusive in these sediments. The great masses of granite 

 which occur in western Burnet and all through Llano county belong to 

 the same age as the strata, and Mr Walcott is careful to remark that he 

 did not observe any rocks of undoubted Archean age in the region. A 

 number of analyses ^^ of the rare minerals of Barringer hill are available, 

 and by ]\Ir Bolt^^ood's rule they give the following ages for the Llano 

 beds : 



Yttrialite, J. B. Mackintosh 11,470 million years. 



Yttrialite, W. F. Hillebrand 5,136 " 



Mackintoshite, W. F. Hillebrand 3,894 " 



Nivenite, Mackintosh 1,671 " 



Fergusonite, Mackintosh , 10,350 " 



Fergusonite, Mackintosh 2,967 " 



Mr Boltwood informs me, however, that, with the possible exception of 

 nivenite, none of these minerals is really suitable for throwing any 

 definite light on the question of the uranium-lead ratio for Llano county, 

 since all of the specimens show signs of incipient or advanced alteration; 

 but, according to theory, the state of combination is without influence on 

 radioactivity, so that the only alterations which would affect the matter 

 must involve, the addition or abstraction of uranium or lead, and mere 

 hydration, for example, should be without effect. The nivenite, inter- 

 preted by the rule, indicates an age 50 times as great as seems admissible 

 from a geological standpoint and 4 times as great as the Glastonbury 

 mineral, which would seem on geological grounds nearly coeval with it. , 

 " There seems to me a plausible explanation of the lack of accord among m 

 these minerals. Mr Brogger,"^ from his exhaustive studies of the Nor- 



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