482 Mr. D. T. Ansted on the Earth's interior Temperature, [May 25, 



kinds of rock. All the rocks may be regarded as metamorphic ; they are, 

 however, stratified, dipping at an angle of 50°, or thereabouts, to the north- 

 west, and corresponding in age to the secondary rocks of England, from the 

 Oxford clay to the Khsetic inclusive. There was very little water met with 

 in tunnelling. 



The observations made by Signor Borelli have been recently made public 

 in a memoir by Signor F. Giordano, that appeared in the Bulletin of the 

 'E. Comitato Geologico d'ltalia' (No. 1, 2, Jan. and Feb. 1871) ; and in 

 this communication the general subject is discussed. The following ac- 

 count, though not a translation of M. Giordano's memoir, derives most of 

 its facts from the statements there made. The geological notes and some 

 of the conclusions, however, result from the author's personal observations, 

 assisted by the account published last year by Professor Sismonda, and a 

 memoir that appeared also last year in the ' Comptes Rendus,' written by 

 M. Elie de Beaumont. 



The temperature observations include the temperature of the air, of the 

 water issuing in springs (always small) met with in the progress of the 

 works, and of the rock. To obtain the latter, borings were made either in 

 the walls of the tunnel or in the headings in advance of the tunnel, and 

 generally to a distance of 7 to 10 feet. The excavation of the complete 

 tunnel from the Italian end was suspended when 6 kilometres had been 

 completed (about 20,000 feet, or less than halfway) ; but as the excava- 

 tion from this end had been much more rapid than from the other, the work 

 was continued by a small heading to a further distance of about 3000 feet, 

 when the opening was made to the work on the French side. Thus several 

 of the observations were made by borings into the wall of the heading, and 

 at a long distance from the completed tunnel and from good ventilation. 



No observations whatever are recorded from the French side of the 

 tunnel, either during the work or at the time of meeting. We are in- 

 formed, however, that a rush of air took place at the moment of the last 

 blast, driving the smoke rapidly towards the Italian end. It should be 

 mentioned that the northern, or French end, is only 11 6 m (3806 feet) 

 above the sea, whereas the Italian end is 1292 m *50 (4241 feet), showing a 

 difference of level of 435 feet. Thus the tunnel would seem to act as a 

 chimney, and it is not unlikely that a natural ventilating-current may be 

 established. 



On the morning of the 26th of December, 1870, the day when the com- 

 munication was made, the external temperature in the Bardonneche valley 

 was considerably below the freezing-point, but within the mouth of the 

 tunnel several degrees above. On this day, besides the temperature of the 

 rock, that of the small springs near the end and that of the air were re- 

 corded ; but the number of men employed, the frequent blasts, and the 

 active works going on must have had a marked influence on the latter, 

 especially as for 3300 feet the excavation of the tunnel had been stopped 

 and only a heading pushed on in advance. During the continuance of the 



