864 



J. BARRELL MEASUREMENTS OF GEOLOGIC TIME 



Uranium Minerals of the Llano District, 'Texas 



Analyses giving Lead-Uranium Ratios 



Used by Becker (1908) 



Arranged in order of increasing ratio ; minor constituents omitted 





A. 



B. 



C. 



D. 



E. 



F. 







6 



|5 





si 



a3 o)^' 



■S2S 



6-i 



U03 



46.75 





3 12 





1 54 



83 



uo, 



19.89 



22.40 



3.93 



*i!64 







T1102 



7.57 



45.30 



83 



10 85 



3 38 



12 00 



ZrO^ 





.88 











Rare earths 



11.22 



1.86 



31.36 



51.70 



42.33 



51.30 



PbO 



10.16 



3.74 



1.94 



.80 



1.43 



0.854 



FCaOs 



0.58 



'i'.is 



3.75 



.76 

 1.96 



0.98 





FeO 



2.89 



SiO^ 







13.90 





29.63 





29.17 



TiO^ 









.05 







Ob^Os 





• • • • • 



42.79 





46.27 





HoO 



2.54 



4.31 



7.57 



.32 



1.98 



6.79 







Total 



. . . . 





99.80 



100.00 



98.95 



• 99.754 



Kef. : Am. Jour. 

 Sci., volume and 

 page 



Year 



38.481. 

 1889 



46.101. 



1893 



38.484. 

 1889 



13.149. 

 1902 



38.483. 

 1889 



38.478, 

 1889 



Pb .. 

 U ... 

 Pb/U 



9.43 i 3.47 

 56.45 \ 19.75 

 .167 I .176^ 



1.80 

 6.06 

 .297 



0.74 

 1.45 

 .513 



1.33 



1.28 

 1.035 



0.79 

 0.69 

 1.147 



A is the same as No. 15 ; B is the same as No. 16. 



A careful review of the original analyses, however, brings to light unex- 

 pected errors and by their elimination results in a good degree of ac- 

 cordance among those minerals whose compositions give indications of a 

 reliable lead-uranium ratio. To demonstrate this statement the following 

 tabulation is given, tlie percentages of lead and uranium and the value of 

 tiieir ratio being the result of recalculations by the writer from the original 

 jniblications of the analyses. It is clearly impossible to give proper weight 

 to the value of the ratio unless the percentage occurj'ences of uranium, 

 lead, thorium, and a number of other constituents are noted. These are 

 assembled and published for this purpose for the first time. 



*2i Given by Becker as .3894, apparently as the result of an arithmetical error. 



