880 M. L. EHe de Beaumount on the Structure and 



of Etna, but still there is one fact which it is necessary to mention. 

 On the 1st October 1834, I visited the extremity of the stream 

 of lava which had issued from the flanks of Etna in the month of 

 November 183J2, that is, twenty-two months and a-half pre- 

 viously. The stream had stopped at two miles from the town 

 of Bronte, on a gently inclined mass, at which point it had ac- 

 cumulated to the height of about twelve yards ; it was still 

 hot in its interior, and on traversing its surface little gusts 

 of extremely hot air issuing from its fissures were every in- 

 stant felt. Besides, there arose from many interstices situated 

 chiefly on the most elevated portions of the unequal surface of 

 the lava^ little streams of watery vapour having a very elevated 

 temperature. These vapours had a strong odour of muriatic 

 acid ; but no traces of sulphurous acid could be distinguished. 

 They deposited on the walls of the fissures a considerable quan- 

 tity of saline substances, and chiefly of muriate of ammonia, 

 which was sometimes perfectly white, and sometimes coloured 

 orange-yellow by the chloruret of iron. At some points the sa- 

 line deposit was slightly coloured green. The muriate of am- 

 monia was sufficiently abundant to enable the man who acted as 

 my guide to gain a livelihood by collecting it. An attentive ex- 

 amination convinced me that the vapour and the saline sub- 

 stances were disengaged from the parts of the lava which were 

 liot yet cooled. The question as to how these substances could 

 remain included in the melted mass during years, is a very dif- 

 ficult problem in molecular physics ; but as to the^ct it seems 

 to me incontestable. 



Among the phenomena presented by all great eruptions, there 

 is one which, notwithstanding my desire to abridge, cannot be 

 passed over in silence. These eruptions are almost always an- 

 nounced by shocks of earthquakes, which shake not only Etna, 

 but often nearly the whole of Sicily. These shocks are not al- 

 ways confined in their effects to simple vibrations, for frequently 

 they are sufficiently violent to fracture the mountain, which thus 

 yields to the force acting on it from below upwards; and to se- 

 parate the walls of the rents thus produced to a greater or less 

 extent, sometimes to a distance of several yards. These rents 

 generally follow vertical planes, wh'ch pass nearly through the 

 the fcxis of the volcanic chimney, and w[»ich cut the suifdce of 



