NOVEMBEE 20, 1908] 



SCIENCE 



711 



Jurassic and Triassic altered sediments 6.4 



Crystalline schists, partly Jurassic and Tri- . . 



assic, partly Archean 7.3 



Monte Leone gneiss and primitive gneiss .... 6.3 



Schistose gneiss (a fold from beneath) 6.5 



Antigorio gneiss 6.8 



The divisional arrangement is Professor 

 Sehardt's. Forty-nine typical rocks are 

 used in obtaining these results, and the ex- 

 periments have been in many cases re- 

 peated on duplicate specimens. Including 

 some very exceptional results, the mean 

 would rise to 9.1 X 10"^^ grams per gram. 



Of the St. Gothard rocks I have ex- 

 amined fifty-one specimens selected to be, 

 as far as attainable, representative.^^ 



Of these, twenty-one are from the cen- 

 tral region, and their mean radium content 

 is just 3.3. The portion of the tunnel 

 from which these rocks come is closely coin- 

 cident with Stapff's thermal subdivision of 

 regions of low temperature.^" This por- 

 tion of the mountain offers the most defi- 

 nite conditions for comparison with the 

 Simplon results. The region south of this 

 is affected by water circulation ; the regions 

 to the north are affected by the high tem- 

 perature of the granite. 



We see, then, that the most definite data 

 at our disposal in comparing the conditions 

 as regards temperature and radio-thermal 

 actions in the two tunnels appear to show 

 that the steeper gradient is associated with 

 the greater radium-content. 



It is possible to arrive at an estimate of 

 the downward extension of the two rock 

 masses (assumed to maintain to the same 

 depth their observed radio-activity), which 

 would account for the difference in 



"I would like to express here my acknowledg- 

 ments to the trustees of the British Museum for 

 granting me permission to use chips of the rocks 

 in their possession; and especially to Mr. Prior 

 for his valuable assistance in selecting the speci- 

 mens. 



" Trans. North of England Mining and Mech. 

 Engineers, XXXIII., p. 25. 



gradient. In making this estimate, we do 

 not assume that the entire heat-flow indi- 

 cated by the gradients is due to radium, 

 but that the difference in radium-content is 

 responsible for the difference of heat-flow. 

 If some of the heat is conducted from an 

 interior source (of whatever origin), we 

 assume that this is alike in both cases. We 

 also assume the conductivities alike. 



Calculating on this basis, the depth re- 

 quired to establish on the radium measure- 

 ments the observed difference in gradients 

 of the Central St. Gothard and of the 

 Simplon, we find the depth to be about 7 

 kilometers on the low mean of the Simplon 

 rocks, and 5 kilometers on the high mean. 

 There is, as I have already said, nothing 

 improbable in such a downward extension 

 of primitive rocks having the radio-activi- 

 ties observed; but as a different distribu- 

 tion of radium may, of course, obtain below 

 our point of observation, the result can 

 only claim to be suggestive. 



Turning specially to the St. Gothard, we 

 find that a temperature problem of much 

 interest arises from the facts recorded. 

 The north end of the tunnel for a distance 

 of 2 kilometers traverses the granite of the 

 Finsteraarhorn massif. It then enters the 

 infolded syncline of the Usernmulde and 

 traverses altered sediments of Trias-Jura 

 age for a distance of about 2 kilometers. 

 After this it enters the crushed and meta- 

 morphosed rocks of the St. Gothard massif, 

 and remains in these rocks for 7^ kilo- 

 meters. The last section is run through 

 the Tessinmulde for 3 kilometers. These 

 rocks are highly altered Mesozoic sedi- 

 ments. 



I have already quoted Stapff's observa- 

 tions as to the variations of gradient in the 

 northern, central and southern parts of the 

 tunnel. He writes : 



They (the isotherms) show irregularities on the 

 south side, which clearly depend on cold springs, 

 they bend down rapidly, and then run smoothly 



