1850.] MURCHISON VENTS OF HOT VAPOUR IN TUSCANY. 3/3 



the connection alluded to becomes much more interesting ; for, as 

 before said, four hot springs boil up in the same linear direction, and 

 it is important to remark, that of these, the spring which is nearest 

 to the lagoni partakes most of their boracic character. In short, the 

 springs and the Soitioni charged with sulphuric, carbonic, and boracic 

 acid, issue upon the very same line ; and in following this line a little 

 further to the S. and by E., we reach Bagni a Morbo, where hot 

 sulphureous springs issue from fissures in rocks similar to those of S. 

 Michele and Monte Cerboli. Still further to the S.S.E. the boracic 

 acid fumes reappear in a remarkably picturesque cleft of the rocks of 

 macigno, at Castel Nuovo, where the linear direction of the vents is 

 very striking*. 



We have thus along a distance of about six or seven English miles 

 from N. and by W. to S. and by E., the clearest possible evidence 

 that the present hot springs and vapours issue upon a hue of fissure, 

 in the alberese and macigno formations, which was formed in very an- 

 cient times, i. e., as I believe, between the eocene and miocene periods ; 

 the production of such fissure having been accompanied by the out- 

 burst of great bosses of serpentine and other plutonic rocks. 



By extending this observation I perceived that the other " Soffioni" 

 of this tract exist under similar conditions, showing either the actual 

 outburst of hot springs and vapours along such line of former erup- 

 tion, or the close parallelism of the two lines of phsenomena. Thus, 

 in my journey to the miocene coal tract of the Maremma before de- 

 scribedf , I found the little town of Monte Rotondo to be built upon 

 a junction of serpentine with the sedimentary strata it had traversed ; 

 and in looking from that spot to the N. and by "W., I saw the va- 

 pours of the Soffioni, which bear the same name, issuing, like those 

 of Lardarello, from a valley encased in flanking ridges of the same hard 

 rocks. Again, the sulphureous lake, about two miles west of Monte 

 Rotondo, having a major ellipse of north and south, is distinctly a 

 prolongation of one of the numerous cracks extending thence to the 

 N. and by W. towards Lustignano, by which boracic acid escapes. 



In mentioning these " Soffioni," Professor Pilla;]; has specially de- 

 scribed those of Sasso, and although he has not noted the coincidence 

 on which I lay so much stress, any one who refers to his woodcut 

 representing the issue at Sasso, will see that the line of vapour issuing 

 from cavities is parallel to the main direction of the encasing ridges §. 

 Now, these ridges of alberese and macigno have either a dominant 

 direction from N. and by W. to S. and by E., or are perforated 

 along such line by the serpentine, granitone (greenstone), or other 

 eruptive rocks, including gabbro, to which I shall afterwards advert ; 

 and hence it appears, that the ancient lines along which nature ex- 

 pended some of her grandest energies in this region, are also those 

 along which she still manifests the present escape of hot springs and 



* This is well described by Targioni Tozzetti. 



t See Quart. Journ. Geol. Soc, vol. v. p. 292. 



% Trattato di Geologia, p. 282. Pisa, 1847. 



§ I cannot but express a hope that Mr. Babbage will at some time give to the 

 public a copy of the suggestions he furnished to the Grand Duke of Tuscany, for 

 the extension of the useful employment of these hot gases, which might thus serve 

 to convert a barren tract into a wealthy manufacturina: district. 



