Products of the Radio-active Elements. 255 



The term secondary uraninite will be used in referring to the 

 material from these latter localities.* 



Among the radio-active minerals other than uraninite which 

 occur as primary constituents of pegmatite may be mentioned 

 thorite, samarskite, fergusonite, aeschynite, euxenite, monazite 

 and the recently describeclf thorianite. Associated with, and 

 obviously resulting from the alteration of, the primary min- 

 erals through the action of percolating waters and other 

 agencies, are secondary minerals, the more prominent of which 

 are gummite, thorogummite, uranophane and autunite. 



In considering the available data on the composition of 

 radio-active minerals, with a view to discovering the ultimate 

 disintegration products of the radio-elements, it is therefore 

 necessary to give strict attention to the question of the prim- 

 ary or secondary origin of the individual specimens and the 

 geological period at which they were formed. The nature of 

 the associated minerals is also usually of considerable signifi- 

 cance, since through them it is frequently possible to discover 

 some clue to the conditions under which the mineral origi- 

 nated and some indication of the influences to which they have 

 been subjected since they were first formed. 



Lead. 



In reviewing the various published analyses of minerals 

 containing notable proportions of uranium, and particularly of 

 those which are evidently of primary origin, one can not fail 

 to be impressed by the frequent and almost invariable occur- 

 rence of lead as one of the other constituents. Out of a con- 

 siderable number of analyses undertaken with the particular 

 object of discovering whether or not lead was present, I have 

 been unable to find a single specimen of a primary mineral 

 containing over two per cent of uranium in which the presence 

 of lead could not be demonstrated by the ordinary analytical 

 methods. The same is moreover true of the secondary ura- 

 nium minerals which have been examined, although in a single 

 case, namely in a small specimen of uranophane from North 

 Carolina, the proportion of lead was so low as to require the 

 working up of a gram of material in order to conclusively 

 demonstrate the presence of lead as a constituent. 



Through a dawning appreciation of the significance of the 

 persistent appearance of this element in uranium minerals, the 

 writer was led to suggest in an earlier paperj that lead might 

 prove to be one of the final, inactive disintegration products 

 of uranium. All the data which have been obtained since 

 that time point to the same conclusion. 



*Hillebrand, this Journal, xl, 384 (1890). 



f Dunstan and Blake, Proc. Eoy. Soc. Lond. (A), lxxvi, 253 (1905). 



X Phil. Mag. (6), ix, 613 (1905). 



