DISTRIBUTION OF RADIOACTIVITY IN DEPTH 141 



over 314 million times the quantity found by ]\Ir Joly in the clay. The 

 data, however, are too few to justify more than the qualitative conclusion 

 that an intelligible tendency is indicated to the concentration of radio- 

 active matter on the sea bottom. On the other hand the depth of the red 

 clay is entirely unknown, and for that reason it seems to me impossible 

 to judge for how long a period radioactive matter has been accumulating 

 in the ocean. 



If a continuous sheet of water is practically impermeable by radium 

 emanation, lakes and ground water must likewise greatly interfere with 

 the escape of this gas; and on land also, so far as ground water exists, 

 there must be a tendency to the concentration of radioactive substances. 

 Eecent studies show that underground waters are more superficial than 

 was formerly supposed, and that meteoric waters are not abundant below 

 a depth of a couple of thousand feet, excepting along certain fissures. 

 The vadose circulation proceeds in most cases with extreme slowness and 

 its waters must interpose a formidable obstruction to the diffusion of 

 radium emanation, or must greatly promote its disintegration within the 

 capillar}- fissures of rock-masses; hence also it seems to me that there 

 must be a concentration of radioactive matter in water-bearing rocks. If 

 so, rocks from desert areas not associated with pegmatite should show on 

 the whole less activity than similar rocks from moist regions; so also 

 rocks collected in very deep mines dry at the bottom should be less active 

 than those of the overlying wet layer, and in general radioactivity should 

 be at a maximum in the outer moist shell of the earth. This is in line 

 with what is known of the radioactivity of volcanic rocks, and the infer- 

 ence is one which ought to be tested by exploration. 



Eadioactive clays at the ocean bottom doubtless evolve heat in the same 

 proportion as they would at sealevel, but the temperature effects must be 

 inconsiderable, because the clays are soaked with very cold water. Con- 

 vection currents will be stimulated to some extent by the heat evolved, and 

 this will be the principal effect. In continental regions also the vadose 

 circulation is equivalent to a water jacket, and radioactive heat will be 

 carried off by the slowly moving water currents. This fact is another 

 reason for believing that the best field for the study of the effects of 

 radioactivity on the earth as a whole is an arid one, such as the Great 

 basin. If the congressional appropriation for chemical and physical 

 research were not so very small, I should endeavor to have a radioactive 

 survey made of the region of the Grand canyon of the Colorado ; but that 

 must wait. 



It appears that uranium and its disintegration products originate in 

 the granitic rocks; that radium must be confined to a relatively thin 



