f34 Scientific InteWgenee. [March, 



by Spallan?ani, who had jierceived the smell Of hydrogen in the 

 gas ; then by your own countryman, Faber, in 17/2 i and since by 

 Lalande and others. Nor has Sir Humphrey in his letter ever 

 mentioned the height of the column of the gas, as stated by you, 

 since this is greater or less according to the state of the atmos- 

 phere, which exerts also much influence on its combustion, it being 

 more vivid at the approach of rainy weather. 



But you were quoting from memory, and under circumstances 

 unfavourable for publication. You may, therefore, probably, be 

 an.xious for some corrections which my knowledge of the country 

 enables me to submit to your judgment. 



The jet of gas alluded to is seen on the top of Monte di Fo, lialf 

 a mile on the right of Pietramala, coming from Florence. The 

 column occupies in circumference a surface of from ten to twelve 

 feet. The ground around it is covered with large and small masses 

 of primitive rocks, or rather of fragments of quartz and mica 

 aro-entine held together by an argillaceous cement, and of lime- 

 stone. Very feeble signs of vegetation are perceptible, either on 

 this or the surrounding mountains. JNIonte Fo forms part of Mount 

 Eadicoso, or of the highest of the Appennine Ridge, being 883 

 metres, or 2iK)l English feet, above the level of the Mediterranean 

 sea. About half a league from this gas-volcano, and from Pietra- 

 mala, there is a well of cold water, called Acqua hija, from which 

 there is a constant evolution of what I myself found to be carbu- 

 reted hydrogen, which takes fire at the approach of a lighted taper, 

 and burns with a brilliant yellcW flame. The Italian naturalists had 

 hitherto considered these emissions of subterraneous gas, by them 

 called fumaiole, to be sulphureted hydrogen, the formation of 

 which they derived from a decomposition of pyrites, that are found 

 in great quantities at a considerable depth in the Appennine country. 

 They fancied they discovered the sulphur, which the decomposition 

 of the gas set at liberty, incrustating the objects surrounding the 

 spot from whence arose the gas ; and I confess having myself been 

 of the same opinion during my last visit to the Appennines in the 

 course of last summer. My examination, however, was very super- 

 ficial, and too hasty to be correct. That of Sir Humphrey Davy is, 

 of course, of quite a diflerent character. 



The Appennines consist chiefly of secondary rocks, amongst 

 which lime-stone containing remains of marine animals is predo- 

 minant. As they, however, approach the Alps, whence they took 

 their origin, they participate more and more of their nature, and 

 present for a long successive tract of ground a mixture of primitive 

 rocks of various species, such as serpentine, argillaceous schist, 

 grunstein, and sacharoid lime-stone. As to the existence of coals 

 in the Appennines, Soldani, in 178O, in his Ornithographic Essay on 

 the Nautilific Formations of Tuscany, mentions a considerable 

 itratum of coal being discovered near Fiesole, a place at the distance 

 of about 40 miles due south from Pietramala. Subsequent exami- 

 nations, however, instituted for the purpose, and directed by very 



