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Show 202 TRAV.ERTTN OF SAN VIGNONE. Baths of San Pignone.-Those persons who . have merely seen the action of petrifying waters in our .own country, will not easily form an adequate conception of the scale on which the same process is exhibited in those regions which lie nearer to the modern centres of vblcanic disturbance. One of the most striking examples of the rapid precipitation of carbonate of lime from thermal waters occurs in the hill of San Yignone in Tuscany, at a short distance from Radicofani, and only a few hundred yards from the high-road between Sienna and Rome. The spring issues from near the summit of a l·ocky hill, about one hundred feet in height. The top of the hill is flat, and stretches in a gently-inclined plateau ~o the foot of Mount Amiata, a lofty eminence, which consists in great part of volcanic products. The fundamental rock, from which the spring issues, is a black slate, with serpentine (b. b. b, diagram 4) belonging to the older Apennine for- Butlts of San Fig1tone. mation. The water is hot, has a str9ng taste, and, when not in very small quantity, is of a bright green colour. So rapid fs the deposition near the source, that in the bottom of a conduit pipe for carrying off the water to the baths, inclined at an angle of 80°, half a foot of solid travertin is formed every year. A more compact rock is produced where the water flows slowly, and the precipitation in winter is said to be more solid and less in quantity by one-fourth than in summer. The roc\ is generally white: some parts of it are compact, and ring to the hammer; others are cellular, and with such cavities as ar~ ~een in the carious part of bone or the siliceous meuliere of thg Paris basin. A portion ~f if also below the village consists o( • long vegetable tubes. Sometimes the travertin assumes preCisely the botroidal and mammillary forrns, com~on _to ~imila~ .l'RAVERTIN OF SAN FILIPPO, . 203. depos. its, in Auvergne' o f a much old d mentiOned; and like th . fi er ate, hereafter to be undulating layers. em lt o ten scales off in thin, slightly A large mass of travertin d where the spring issues and escfnds the hill from the point half a mile east of S~n v· reac les to the distance of about of tl~e hill at about an ang{!:~n~o The beds take the slope ncatiOn are perfectly parallel 0 and the planes of strati-many layers, is of a compact n. t ne stratum, composed of a ure and fif £" s. er1ve s as an excellent b ')d' teen 1eet thick. 't UI mg stone d ' I m ength was, in 1828 c t £' ' an a mass of fifteen feet 0 . ' u out wr th . rcia. Another brancll f . e new bridge over the th ~west, o 1 t (a. a d. for two hundred and fif i' ~~gram 4,) descends to thickness, but sometimes two hu ~y J~t In length, of varying offby the small river Orcia r . n re eet deep; it is then cut land descend into a valley ;ih :~~~ely as some glaciers in Switzer by a transverse stream of eir progress is suddenly arrested-tl water. Th b. . le mass of rock at the river 1 • ~ a 1 upt ternnnation of clearly shews that it would ' ~ 1endits thickness is undiminished by th e stream, over which iptr oimce ee much. fia rt h er I. f not arrested' encro.ach upon the channel of the ngs ~hghtl.y. But it cannot dermmed, so that its solid fra men" rcta, bemg constantly unthe alluvial gravel. H g LS are seen strewed amon t lid owever enormo I gs so . rock may appear which h b us_, t lerefore, the mass of sprmg w £" as een gtven o t b h' · h ' e may leel assured that it . . . . u y t Is smgle ~ e~ compared to that which h b Is msJ~mficant in volume t e time when it began to iJow as een earned to the sea sine~ of tha~ period of time, we ha~·e :-hat may have been the length quarrymgthe travertin, Roman flo ~ata for conjecturing. In at the depth of five or six feet. 1 es ave been sometimes found Baths of San p,·z· ~·~ that last me~~~~:d-?~ anther bill, not many miles rniata, the summit of w'hi 1 . a so connected with Mount roc arek the c~lebrated baths o~ 1 Sis abFo~~~ three miles distant serp s fc onsist f 1 an 1 tppo Th . , o a ternations of bl k ] . e subJacent nine e~o~:' t~f highly inclined strata a~e] s a~e, limestone, and of a Ion; and, as at S . ,_ ongmg to the A en bl a tertiary basin of . an VIgnone, near the boundp - ue a 'll marine ori · . . ary rgi aceous marl. 'l'her gm, consistmg chiefJ of e are .three w~rm sprm. gs hYer e, |
