870 



J. BARRELL MEASUREMENTS OF GEOLOGIC TIME 



Table D 

 Radioactive Minerals from Llano County, Texas, United States of America "* 



Analyst. 



Mineral. 



Lead. 



Uranium 



Pb/Ur. 



i Mackiiitosli 



Yttrialite 



0.8 



0.8 

 1.3 

 0.76 

 1.8 

 3.65 

 10.25 

 3.47 

 9.4 

 9.45 

 7.82 

 2.01 



0.71 

 0.75 

 1.28 

 1.5 

 6.14 

 19.6 

 55.2 

 19.7 

 55.0 

 56.1 

 67.2 

 19.7 



1 13 



2. Mackintosh 



Yttrialite 



1.07 



3. Mackintosh 



4 Hillebrand 



Fergusonite 



Yttrialite 



Fergusonite 



Mackintoshite 



Cleveite 



1.01 

 0.51 



5. Mackintosli 



6. Hillel)ran<l 



0.29 

 0.186 



7 Mackintosh 



0.186 



S. Hillebrand 



Mackintoshite 



Uraninite 



Nivenite 



Broffgerite 



0.176 



9. Hillebrand 



0.170 



10. Mackintosh 



11. Mackintosh 



0.168 

 0.116 



12. Mackintosh 



Thorogummite 



0.102 



Number 1 appears to be F of Becker's list. 



Number 2 the writer has not been able to identify. 



Number 3 is E of Becker^s list. 



Number 4 is D of Becker's list. 



Number 5 is C of Becker's list. 



Number 6 appears to be from an incomplete analysis by Hillebrand : Amer- 

 ican Journal of Science, volume 46, page 101, analysis I). The thorium and 

 1 ire earths were lost, and Hillebrand states that the percentage of UO, would 

 be slightly increased by uranium which was not separated from the earths. 

 The analysis therefore has no value as compared with number 8. 



Number 7 is not from I^lano County, but apparently from Norway. It is 

 given on page 482, American Journal of Science, volume 38, 1889, for purposes 

 of comparison with nivenite. The analyst was Lindstrom, as given in Dana's 

 System of Mineralogy, edition of 1911, pages 890, 891. The responsibility for 

 the error rests in greater part on Mackintosh, as it is only by reading the text 

 that one discovers that this is not the analysis of a local mineral. Dana also 

 was misled and incorrectly lists it as coming from Texas. 



Number 8 is B, Becker's list, and number 16 of Boltwood's list. 



Number 9 is number 14 of Boltwood's list. 



Numher 10 is A, Becker's list, and number 15 of Boltwood's list. 



Number 11 is another Norwegian mineral given by Mackintosh for compari- 

 son with nivenite. The analyst was Blomstrand. The same errors have been 

 made as in number 7. 



Number 12, thorogummite, occurs as a yellowish brown alteration product 

 of mackintoshite. It is thoroughly oxidized and hydrated. It seems to be a 

 product of recent oxidizing waters, and although it retains a chemical resem- 

 blance to the original mineral it has lost over 1 per cent of its lead. Accord- 

 ing to the calculations of the writer, the uranium is 18.76 per cent, not 19.7, as 

 Holmes has it. This is due to the lesser proportion of uranium in the higher 

 oxide. The uranium has therefore also decreased about 1 per cent, but an 



1^" Am. Jour. Sci., vol. xxviii, 1884, pp. 431-433 ; vol. xxxviii, 1889, p. 480 ; vol. xlvi, 

 1893, p. 98. 



