Mineral Springs of Colorado. 637 



tions show that quite extensive open underground water 

 channels are not uncommon and it is quite evident that 

 many of the hot springs flow for long distances in such 

 courses. In a water course which permits free and rapid 

 flow, radium emanation could be absorbed at a great dis- 

 tance and brought to the surface without losing greatly 

 through disintegration. Likewise a rapid flow through a 

 long underground channel could give at the outlet a very 

 active water or gas which need not have encountered any 

 particularly active material. In the case of slow seepage 

 flows which may collect in an open channel extending only 

 a short distance from the outlet or which may empty into 

 the pool which forms the spring itself, most of the emana- 

 tion is undoubtedly collected not far away. Even 

 though such a spring should show high activity it does 

 not mean necessarily that there is highly active material 

 near by. The slow flow and shorter distance of travel 

 are compensated by the greater area of the underground 

 stream and by its intimate contact with a greater amount 

 of weakly emanating material. 



The foregoing argument of course does not exclude the 

 possibility of the underground flow touching very active 

 substances but the presence of such material can not be 

 inferred from the existence of a highly radioactive water 

 or gas without other evidence. If a spring happened to 

 be so situated that its waters came in contact with a mate- 

 rial which could be classified as even a low grade radio- 

 active ore, and further if it had the large and rapid flow 

 characteristic of most of the springs examined in this 

 work, it seems fairly certain that it would show an activity 

 of a different order of magnitude from those recorded in 

 the tables above. 



My thanks are due to Professor R. D. G-eorge, Direc- 

 tor of the Colorado State Geological Survey, and to his 

 assistants for help in meeting many unexpected difficul- 

 ties. The Survey has also furnished important informa- 

 tion regarding geological formations. 



During the work in the field courtesies were extended 

 by Dr. R. B. Moore and Dr. S. C. Lind of the United 

 States Bureau of Mines, and by Professor L. F. Miller 

 formerly of the Colorado School of Mines. 



For the drawings accompanying this paper the author 

 is indebted to Mr. J. H. V. Finney. 



Hale Physical Laboratory, University of Colorado, Boulder, Colorado. 



Am. Jour. Sci. — Fourth Series, Vol. XLVI, No. 275. — November, 1918. 

 29 



