6 PEOCEEDINGS OF THE NATIOlTAIi MUSEUM 



The results are given in tabular form below : 



VOL. 72 





D. P. S. per g. 



Ra per g.XlO' 



Chamber No. 



standard 

 pitch- 

 blende 



Carnotite 



Standard 



Carnotite 



Upper g 

 carnotite 



5xio-T 





r30. 579 

 130. 148 



17. 152 

 17. 132 











1 _ 

























Average — 



30. 364 



17. 140 



2.248 



1.269 



0. 5460 



2.32 





/32. 027 

 131. 720 



17. 622 



17. 774 











2 

























Average 



31. 873 



17. 648 



2.248 



1.244 



0. 5460 



/ 2.28 

 1 2.30 



You will notice that the Ra:U ratio (2.30X10"'') is only about 68 per cent 

 of the normal ratio (3.40X10-') determined by Lind and Roberts. 



From Mr. Davis's determination that the radioactivity is about 

 68 per cent of that present when radium is in equilibrium, it follows 

 that the mineral is about 6,800,000 years old — say 7,000,000 years, 

 and such a figure accords well with the geology of the deposit. 



The ordinary carnotites of the region show as much as 0.80 per 

 cent PbO, indicating an age of about 42,000,000 years.^ Owing to 

 the movement of the mineral the lead here too is probably lower 

 than it would be if the mineral occupied exactly its original position. 



The Grand Canyon of the Colorado, although much deeper and 

 more imposing farther down the river, nevertheless has a very con- 

 siderable development at Moab, where the drainage from Bridger 

 Jack joins the main stream. Concerning the age of the Grand 

 Canyon in j^ears, Dutton ^ said : 



No doubt the question will often be asked, how long has been the time 

 occupied in the excavation of the Grand Canyon? Unfortunately there is no 

 mystery more inscrutable than the duration of geological time. On this point 

 geologists have obtained no satisfactory results in any part of the world. 

 Whatever periods may have been assigned to the antiquity of past events have 

 been assigned provisionally only, and the inferences are almost purely hypo- 

 thetical. In the Plateau country, Nature, has, in some respects, been far more 

 communicative than in other regions, and has answered many questions far 

 more fully and graciously. But here, as elsewhere, whenever we interrogate 

 her about time other than relative, her lips are sternly closed, and her face 

 becomes as the face of the Sphinx. 



Through the crystallized carnotite just described Nature partly 

 answers the question of age. Possibly other discoveries of radio- 

 active minerals will allow a still further determination of the age 

 of the Colorado Canyon as they do of many other earth features. 



' Hess, Frank L. New and known minerals from the Utah-Colorado carnotite region. 

 U. S. Geo]. Survey Bull. 750, p. 78, 1924. 



8 Dutton, C. E., U. S. Geol. Survey, Second Ann. Rep., p. 166. 



o 



