368 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 27, 



Hot vapour vents. — If the intensely hot vapour gusts which have 

 issued for centuries from cavities in the rocks of the Tuscan jNIaremma 

 had been as well known to Dante, as they were to Targioni Tozzetti 

 their graphic describer in the last century, the great poet would 

 surely have selected them as a finer illustration of infernal agency 

 than the feeble " bullicami " of Viterbo *. In our own day the chief 

 features of the Tuscan escapes of hot gases impregnated with mineral 

 acids have already been described by Mr. Babbage in Murray's 

 * Hand-book of Central Italy/ and subsequently they have been 

 connected with a geological sketch of other parts of Tuscany by Mr. 

 W. J. Hamilton, Sec. G.S.f In order, however, to render my own 

 view clear, I must offer a slight outline of the chief phsenom.ena. 



In addition to other substances, the hot vapours of Tuscany are 

 charged with boracic acid, known only elsewhere in the active vol- 

 cano of Stromboh. For the extraction of this last-mentioned salt, 

 the extensive w^orks of M. Lardarel have been entered upon at the 

 following nine localities : viz. Lardarello or Monte Cerboli, Lustig- 

 nano, Monte Rotondo, Sasso, II Lago, Castel Nuovo, St. Federigo, 

 and St. Ippolito. These places are all situated in that elevated 

 northern portion of the Tuscan INIaremma which lies on the left bank 

 of the Cecina. Thence the affluents of that river (the Pavone, 

 Posera, Trossa, and Sterza) flow northwards ; whilst the Cornia and 

 its feeder the Melia run down to the Mediterranean in a westerly 

 and southerly direction. The tract, penetrated at intervals by the 

 hot gases, has a length of about eight geographical miles from 

 N.N.W. to S.S.E., and a breadth of about five miles from W.S.W. 

 to E.N.E. ; the whole being comprised withm 43° 8' and 43° 16' 

 N. lat. 



Subtended generally on the E. and N. by the Cecina, this hilly 

 tract, which is much fissured from N. 15° W. to S. 15° E., is sepa- 

 rated on the east from the deep valley in which that river runs by 

 a lofty ridge extending from ]Monte Castelli on the N.N.W. to the 

 Gerfalco mountain on the S.S.E. ; whilst another but lower ridge 

 parallel to the above, is seen upon the western side of the gaseous 

 district passing from jMonte Rufoli to Lustignauo, whence it slopes 

 down to the sea-coast between Leghorn and Piombino. The gaseous 

 vents occur therefore in an elevated and broken trough, on lines 

 more or less parallel to the older flanking ridges. The general cha- 

 racter and age of the sedimentary deposits of this region have been 

 recently explained by myself J. It is enough then, for my present pur- 

 pose, to state, that although the adjacent and undulating hills and 

 valleys abound in marls and sands of tertiary subapennine age, and 

 that to the south the lowest member of these accumulations is charged 

 with coal of miocene age, the upland tract now under consideration, 

 and from which the boracic acid fumes issue, is chiefly composed of 

 the rocks called Alberese and INIacigno. The latter containmg Num- 

 mulites, represents, in my opinion, the eocene, and the former be- 



* See LyelFs Principles of Geology, 7th ed. p. 243. 



t Quarterly Journal of the Geological Society, vol. i. p. 295. 



X Ibid. vol. V. p. 276 et seq. 



