Notices of Memoirs — The Si. Gothmxl Tunnel. 81 



given as to the mode of excavation, and then the geological structure 

 is considered. The rock section vv^as found to be much the same as 

 the preliminary investigations had indicated, consisting of granitoid 

 gneiss, black schist, micaceous felsites with a small quantity of 

 cipollino and other calcareous rocks in the large U folds under the 

 Ursern and Ticino valleys. The fan structure, so general in all 

 the Alpine ranges, was very marked, the strata spreading out in the 

 St. Grothard mountain, and forming north and south the two U folds 

 mentioned. It was in this northern fold under the Ursern valley 

 that the greatest difficulties of the undertaking were met with, for 

 the Ursern gneiss was found to be decomposed down to a very con- 

 siderable depth, here over a thousand feet below the surface, so that 

 the felspar had become a soft clay, and in consequence the expense 

 was raised from about 3,500 or 4,000 up to 20,000 francs a metre. 



But the most interesting results of the undertaking are the obser- 

 vations made on the temperature of the air in the tunnel, together 

 with comparisons of the temperature of the air and the earth at the 

 surface. The figures of the temperature of the air are from observa- 

 tions taken in meteorological stations on the route, and in order to 

 obtain the temperature of the earth at the surface, the temperature 

 of the streams were measured and calculations were made from a 

 large series of such observations. 



The increase of temperature in the Mont Cenis tunnel was shown 

 to be 1° Centigrade in each 51^ metres below the surface, which 

 increment was less than was expected from previous data, mostly 

 obtained in mines and borings. The St. Gothard measurements 

 give 1° C in about each 52 metres, thus both very closely cor- 

 respond, considering that there are always modifying circumstances, 

 as, for instance, decomposition of the rock where pyrites and other 

 substances occur. The maximum temperature was 30-5° 0. under 

 1700 metres of rock, and the increase of temperature is shown to 

 vary approximately with the profile of the mountain mass above, 

 though somewhat modified by the surrounding mountains. 



A very interesting concluding chapter deals with the lessons 

 which may be learnt from this gigantic enterprise, and as the health 

 of the workmen has in this case been very seriously affected by the 

 unfavourable condition of work, it is evident that means must be 

 taken to improve the ventilation in any similar undertaking, and 

 Giordano considers that the Belgian system of making the advance 

 gallery at the tojD gives less satisfactoi'y results in this respect than 

 the English system, where the preliminary gallery is at the base of 

 the future tunnel, and as at present tunnels are proposed both 

 through the Simplon and Mont Blanc, these questions have a 

 practical importance. 



The Simplon tunnel, according to one plan, would pass under a 

 superincumbent mass of 2250 metres, and this, according to the 

 law now formulated regarding the increase of temperature, would 

 give 47° C. in the middle of the tunnel ; according to another 

 proposition the tunnel would be at a greater altitude, and would 



DECADE II. VOL. VIII. — NO. II. 6 



