396 



J. C. Sanderson — Radio-active Content of 



natural soils ; i. e., about 10~ 5 gram of thorium per cubic centi- 

 meter. Runs with this strength and with twice this strength 

 yielded the same value of K, but when the strength was raised 

 to 5xl0" 5 gram, the value of K fell off by about thirty per 

 cent;, showing that the critical thickness of film had been 

 passed. 



Name 



£1 



Ra 

 gram 



X 



10 14 



Th 

 gram 



X 



10 7 



Th/ 

 /Ra 



X 



io- 5 



-1-3 



Oh 

 <D 

 ft 



Character of Soil 



Cyrus 



A 



80 



64 



80 



Surf. 



Red River Valley ; bowlder-ciay ; 

 late Wisconsin drift. 



University Farm 



A 



75 



71 



95 



3 



feet 



Till coating on outwashed plain 

 from late Wisconsin drift. 



Preston 



A 



64 



47 



73 



3 

 feet 



Loess. 



Luverne 



A 



64 



41 



64 



3 



feet 



Surf. 



Loess. 



Manitoba J'nc'n 



A 



62 



60 



97 



Red River Valley ; bowlder- clay ; 

 late Wisconsin drift. 



Coon Creek 



B 



28 



27 



96 



3 



feet 



Dune Sand. 



Guthrie 



B 



27 



25 



93 



Surf. 



Outwashed plain from late Wis- 

 consin drift. 



Bemidji 



B 



25 



34 



136 



3 



feet 



Outwashed plain from late Wis- 

 consin drift. 



Nickerson 



B 



24 



32 



133 



Surf. 



Sandy deposit on moraine from 

 early Wisconsin drift. 



Willow River 



B 



20 



33 



160 



Surf. 



Outwashed plain from early Wis- 

 consin drift. 



Philbrook 



B 



20 



29 



145 



Surf. 



Outwashed plain from late Wis- 

 consin drift. 



Twin Valley 



B, 



17 



28 



165 



Surf. 



Sandy plain ; Lake Agassiz ; rich 

 in nitrogen. 



Cloquet 



B 



13 



32 



246 



Surf. 



Moraine from early Wisconsin 

 drift. 



Discussion of Hesidts. 



The results of the radium and thorium measurements, as 

 well as some data with regard to the fertility, origin, etc., of 

 the soils, are given in the table. 



Quite a wide range of variation will be noticed in the radium 

 content of the soils ; the lowest value is well above that found 



