present in Bocks in the Neighbourhood of Montreal. 235 



Boltwood in their determination of the amount of radium 

 associated with uranium in radioactive minerals. It was 

 prepared from some radium bromide which Rutherford and 

 Barnes found gave per gram a heating effect of 110 gram- 

 calories per hour. 



The solutions prepared from the specimens of Montreal 

 rocks were tested two or three times to insure accuracy. The 

 results obtained were as follows : — 



Period. 



Bocks in order of age 





Grams of Radium 



of formation. 





per gram of rock. 



Ordovician ... 



Trenton limestone, 

 crystalline 



Sedimentary. 



—12 

 ■92x10 



,, 



Trent limestone, 



J5 



•91 





weathered. 







^Devonian ? ... 



Essexite. 



Igneous. 



•26 



,, 



Tinguaite. 



,, 



4-3 



,, 



Tinguaite (different 



,, 



30 





locality). 







,) 



Nepheline syenite. 



,, 



11 



Quaternary ... 



Boulder-Clay. 



Sedimentary. 



•80 



>> 



Leda-Olay. 



M 



•78 



" 



Saxicava-Sand. 



" 



•16 



* These igneous rocks ail cut the Upper Silurian, and are of late Palaeozoic 

 age, probably Devonian. 



The mean of these values is 1*1 x 10~ 12 , and as this result 

 is of the same order as that obtained by Strutt (1*4 x 10~ 12 ) 

 we did not think it necessary to examine a larger number of 

 specimens. 



It will be noted that in every case the substances examined 

 contained much more radium than that required to account 

 for the existing temperature gradient of the earth. It is 

 difficult to understand how the earth can have remained at 

 its present temperature when radium is so plentifully dis- 

 tributed in the constituents of the earth's mass. There appear 

 to have been three explanations offered : — 



1. Strutt has suggested that the interior of the earth is 

 different in constitution to the earth's crust. The great 

 density of the earth lends some weight to this suggestion. 

 Moreover, Milne finds further support to this hypothesis in 

 the rate of propagation of earthquake waves. 



2. It has been conjectured that the disintegration of radium 

 is retarded or stopped under the extreme pressure in the 

 earth's interior. If that is so, the heating effect of the radium 

 would also be diminished. This suggestion is capable of 

 experimental test. In the meantime it may be remarked 



R2 



