690 TRANSACTIONS OF SECTION C. 



his preference for the view that the exoeas of teiuparatiire iu the granite is due tp 

 mechanical actions to which the granite was exposed daring tha upheaval of this 

 region of the Alps. 



The accompanying diagram shows the distribution of temperature as given by 

 Stapff, and the distribution of radium as found from typical specimens of the 

 rocks. There is a correspondence between the two which is obvious, and when 

 it is remembered that the increase in radio-activity shown at the south end 

 would have been, according to Staptf", masked by water circulation, the correspond- 

 ence becomes the more striking. The small radium values in the central parts of 

 the tunnel are remarkable. The rocks of the Central St. Gothard massif are 

 apparently exceptionally poor in radium. 



At the north end the excess of radium is almost confined to the granite, the 

 rock to which Staplf ascribed the exceptional temperatures. The radium of the 

 Usernmulde is probably not very important, seeing that these sediments cannot 

 extend far downwards. The principal local source of heat appears located more 

 especially beneath the synclinal fold, for Staptf's table (loc. cit., p. 31) of the 

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

 ii,500 metres from the north entrance of the tunnel. It is observable that the 

 radio-activity of the granite increases as it approaches the Usernmulde and attains 

 its maximum (141) 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 77 



Usernmulde ........ i'D 



St. Gothard massif 3'9 



Tessinmulde 34 



The central section, however, if considered without reference to geological 

 demarcations, would, as already observed, come out as barely 3 3. And this is 

 the value of the radio-activity most nearly applicable to Staptf's thermal sub- 

 division of the region of low temperature. 



If we accept the higher readings obtained iu the granite as indicative of the 

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

 of the difference of heat- flow from the central and northern parts of the tunnel is 

 obtained. Using the difl!erence of gradient as basis of calculation, as before, we 

 find that a downward extension of about six thousand metres would, if the out- 

 flow took place in an approximately vertical direcliou, account for the facts 

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

 ward extension of the St. Gothard rocks as derived from the comparison with the 

 Simplon rocks. 



VVe 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 which thus similarly localises radium and tem- 

 perature in roughly proportional amounts, and permits us, without undue assump- 

 tions, to explain such remarkable differences of gradient. There is much work to 

 be done in this direction, for well-known cases exist where exceptional gradients 

 in deep borings have been encountered — exceptional both as regards excess and 

 deficiency. 



Eadio-active De2wsits 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. 



The history of mountain building has repeated itself many times: ages of 

 sedimentation, with attendant sin"king of the crust in the area of deposition, 

 then upheaval, folding up of the great beds of sediment, and even their over- 

 thrusting for many miles. So that the mountain ranges of the world are not 

 constituted from materials rising from below, save in so far as these may form a 



