Sir R. I. Murchison on the Vents of Hot Vapour in Tuscamj. 53 



falco, as well as the ridges of Monte Calvi and Campiglia on the west, 

 are both of Jurassic age, the Ammonites Conyheari, Sow. and A. cos- 

 tatus, Schkh. occurring iu them. 



All these sedimentary rocks, from the Jurassic to those of the eocene 

 group inclusive, hare "been penetrated, and for the most part much 

 altered, by igneous or plutonic rocks, the greater number of which 

 have a serpentinous character, their prevailing direction being equally 

 N.^A^ and by N., S.E. and by S. Upon entering this elevated tract 

 from the north, I found that its chief town, Pomarancia*, was si- 

 tuated on a plateau of shelly, tufaceous, yellowish, sandy marlstone 

 —in parts a travertine. Tliis band clearly overlies the subapennine 

 marls of the adjacent hills and valleys on the north, in which the 

 rock salt and springs of Volterra occur, and is probably of the same 

 age as the uppermost yellow marine ' panchina ' of Tuscany, or as 

 the lacustrine deposit in the valley of the Elsa, to which I have alluded 

 in a previous memoir f- 



The rock is disposed in horizontal masses, and denuded into abrupt 

 escarpments, which in the middle ages formed the natural defences 

 of the old feudal town. This tertiary deposit occupies the tract 

 between the picturesque heights of Rocca Sillana on the east, the 

 hot springs of S. Michele on the west, and Monte Cerboli on the 

 south, where rocks of serpentine and gabbro rise up through strata 

 of whitish grey alberese limestone and some contiguous schists and 

 sandstone. It is near the junction of the intrusive rocks of serpen- 

 tine with the depositary strata, which are there much contorted and 

 broken, that certain hot springs appear ; four of which, at INIonte 

 Cerboli, have recently been made known and their contents analysed 

 by Professor Targioni Tozzetti;}:. His observations and analysis 

 are of geological importance, inasmuch as they show that those 

 springs which appear at intervals between INIonte Cerboli (Mons 

 Cerberus ?) and Lardarello, where the vapours issue, define a line, as 

 he says, from N. to S. (but accurately N. and by W., S. and by 

 E.), and that essentially the springs contain, though in different 

 proportions in each, the same ingredients as the lagoni or vapours 

 to the south of them. Thus, exclusive of organic and bituminous 

 matter, all the wells contain chloride of sodium, carbonate of 



* Pomarancia is the chief residence of Count Lardarel, the spirited and hospi- 

 table proprietor of the boracic acid establishments. 



t Quart. Jourii. Geol. Soc. Lond. vol. v. p. 291. 



t Delle acque-termo miuerali de Monte Cerboli. Firenze, 1846. Estratta della 

 Gazzetta Toscana delle ScienzeMedico-li!,iche, An. 4. 2. 1. In this memoir the 

 reader will find indications that the vai^urs of boracic acid had no issue in the 

 beginning of the sixteenth century. See also notice of this tract by the early 

 geological traveUer Targioni Tozzetti (Viaggi), whose descendant, the bviug Pro- 

 fessor of Chemistry in Florence, has also puljlished analytical descriptions of the 

 waters 6f Mont Alceto, Uapolano, Monte Catini, Castrocasa, Cimiano, and Casale. 



Since writing the memoir I liave been informed by Dr. Uaubeny that the 

 boracic acid vapours contain nitrogen gas — thus sustaining his views on the 

 origin of volcanic action. [M. Paycii in his interesting account of the manufacture 

 of boracic acid in Tuscany gives the foll.iwiug as the com|)osition of the non-con- 

 densed gases in 100 parts :— carbonic acid, r)7'30 ; nitrogen, 34-81 ; oxygen, 05/ ; 

 and sulpluirelled hydrogen, 1-32. — W. I".] 



