44 



Prof. J. Prestwicli 



In the St. Gothard tunnel, where very fall and complete observa- 

 tions were carried out by Dr. Stapff, the results are of much interest. 

 The tunnel is about 9 miles long; the summit level of the ridge 

 above the tunnel is 10,040 feet above the sea level, and 5578 feet 

 above the tunnel. This, after allowing for the convexity of the 

 surface, gave a rate of increase of 1° P. in 82 feet. But Dr. Staph 2 * 

 has since pointed out that in one part of the tunnel the rate is 

 considerably more rapid. He found that the relative tempera- 

 ture of the ground above the northern end of the tunnel was much 

 higher than in other parts — that in the plain of Andermatt the 

 mean rock temperature was several degrees above the normal, while 

 at the south end of the tunnel it was some degrees below it. The 

 latter circumstance was easily explained by the presence of cold 

 springs ; and some higher temperatures in other parts of the tunnel 

 were attributable to the decomposition of the rock ; but there were no 

 apparent reasons for this excess of temperature in the northern end 

 of the tunnel, where it passes through gneiss and granite. The 

 difference was such that instead of a rate of increase of 1° in 85 feet in 

 the centre of the tunnel, or of an average rate of increase for the 

 whole tunnel estimated by him at 57'8 feet, the rate was here 1° F. in 

 38 feet. Dr. Staph says that there is no obvious explanation of the 

 rapid increase in the granite rocks at this end of the tunnel, and that 

 it is probably to be attributed to the influence of different thermal 

 qualities of the rock. He mentions, further, that this granite be- 

 longs to the massif of the Pinsteraarhorn, which is of a different 

 (newer) geological age to that of the central axis of St. Gothard, and 

 that it is therefore not to be wondered at " if one of them be cooler 

 than the other." He elsewhere remarks that there is also a well- 

 known local focus of heat (decomposition of rock) below the valley of 

 Andermatt, which may exercise a sufficient influence. 



I myself am disposed to attribute the greater heat of these rocks to 

 mechanical action rather than to the later protrusion of the Plutonic 

 rocks, or to any subsequent decomposition of these rocks. If the 

 pressure, force, and friction accompanying elevation of mountain 

 chains be attended by the development of great heat — a heat sufficient 

 to produce great chemical changes even in the Tertiary strata — then 

 it may be possible for some of the newer mountain chains still to 

 retain a portion of that heat. The facts brought forward by Dr. 

 Stapff in the St. Gothard tunnel give material support to this view. 



Although Mallet failed to show that the heat produced in the crush- 

 ing of rocks by the lateral pressure, arising from the contraction of the 

 crust of the earth as a consequence of its slow secular refrigeration, 



* " Trans. North, of England Inst. Min. and Mechan. Engineers," toI. xxxiii 

 (1883), p. 19. 



