Mineral Springs of Colorado. 635 



Yellowstone National Park and is approached by but two 

 or three European springs. 



A careful comparison of the radioactivity measure- 

 ments with the data obtained from the chemical analyses 

 shows that there is no connection between radioactivity 

 and any chemical property. Neither is there any con- 

 nection between activity and temperature, nor between 

 the activity in water or gas and that in the deposits. 

 Some springs situated near each other have shown activ- 

 ities of very different magnitude and again the individual 

 springs of a closely associated group have shown quite 

 similar activities. In the first case the waters of the 

 separate springs usually had the appearance of being 

 different in character but not always. 



Results similar to the foregoing have been recorded by 

 many previous observers both in this country and in 

 Europe. There is a general agreement that springs from 

 igneous rocks are more active than those from sedi- 

 mentary rocks. 11 If we take the ninety-five springs of 

 Table I which show an emanation content equal to or 

 greater than 10 X 10~ 10 curie per liter we find that 58 or 61 

 per cent are in pre-Cambrian formations or near a pre- 

 Cambrian contact ; 14 or 14-7 per cent are in igneous rock 

 or near igneous and sedimentary contacts; 23 or 24-2 

 per cent are in sedimentaries of various formations. 

 Approximately 75 per cent of the more active springs 

 are thus in or near metamorphic and igneous formations. 

 Some of the most active springs, however, are found in 

 sedimentaries. Nos. 73-77 in the Cretaceous and Nos. 

 136-139 in the Miocene are examples. 



At the beginning of this investigation it was antici- 

 pated that some springs of extraordinarily high radio- 

 activity would be found since Colorado contains quite 

 extensive deposits of radioactive ores. This expectation, 

 however, was not fulfilled. No large mineral springs 

 were found in regions where radioactive ores are most 

 abundant. . A number of springs, often highly gaseous, 

 situated not far outside such regions showed in general 

 the least activity of any examined. On the other hand, 

 some quite active springs such as Nos. 107-109 near 



11 Since this article was written there has appeared an extensive inves- 

 tigation on the Kadio-activity of Archean Eoeks from the Mysore State by 

 Smeeth and Watson (Phil. Mag., 35, 206, 1918). All these rocks, considered 

 to be of igneous origin, contain remarkably little radium. The various 

 igneous magmas not only appear to contain different amounts of radium 

 but the radioactive material seems to be subject to magmatic segregation. 



