URANIUM AND GEOLOGY JOLY. 375 



tures. The radium of the Usernmulde is probably not very important, 

 seeing that these sediments can not extend far doAvnward. The prin- 

 cipal local source of heat appears located more especially beneath the 

 synclinal fold, for Stapff's table (loc. cit., p. 31) of the gradients 

 beneath the plain of Andermatt shows a rising gradient to a point 

 about 2,500 meters from the north entrance of the tunnel. It is 

 observable that the radio-activity of the granite increases as it ap- 

 l^roaches the Usernmulde and attains its maximum (14.1) where it 

 dips beneath the syncline. 



The means of radium content in the several geological sections into 

 which the course of the tunnel is divisible are as follows : 



Granite of Finsteraarhorn 7. 7 



Usernmulde 4. 9 



St. Gothard massif 3.9 



Tessinmulde 3. 4 



The central section, however, if considered without reference to 

 geological demarcations, Avould, as already observed, come out as 

 barely 3.3. And this is the value of the radio-activity most nearly 

 applicable to Stapff' s thermal subdivision of the region of low tem- 

 perature. 



If we accept the higher readings obtained in the granite as indica- 

 tive of the radio-active state of this rock beneath the Usernmulde, a 

 satisfactory explanation of the difference of heat flow from the cen- 

 tral and northern parts of the tunnel is obtained. Using the differ- 

 ence of gradient as basis of calculation, as before, we find that a 

 downward extension of about 6,000 meters would, if the outflow took 

 place in an approximately vertical direction, account for the facts 

 observed by Stapft'. This depth is in agreement with the result as to 

 the downward extension of the St. Gothard rocks as derived from the 

 comparison with the Simplon rocks. 



We are by no means in a position to found dogmatic conclusions on 

 such results; they can only be regarded as encouragement to pursue 

 the matter further. The coincidence must be remarkable, however, 

 which thus similarly localizes radium and temperature in roughly 

 proportional amounts, and permits us, without undue assumptions, to 

 explain such remarkable differences of gradient. There is much work 

 to be done in this direction, for well-known cases exist w^iere excep- 

 tional gradients in deep borings have been encountered — exceptional 

 both as regards excess and deficiency. 



RADIO-ACTIVE DEPOSITS AND THE INSTABILITY OF THE CRUST. 



At the meeting of the British association held last year at Leicester 

 I read a note on the thermal effects which might be expected to arise 

 at the base of a sedimentary accumulation of great thickness due to 

 the contained radium. 



88292— SM 1908 25 



