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Show 20G CALCAREOUS PRRCTPil'ATES 't the different layers contm. ue of the same thickness, and pgrreasveir vye; the original form of the nucleus. l . · ,f Vt.l er bo .-W e m ust not attempt to des· cri~ef Bu lCamt ~J. . 1 where the constant formation o aU the localities m Ita y th Silaro near Prestum, on the limestone may be seen ' as on e ' · h 1 B licami or hot baths m t e Velino at T erm., a nd near t le u' l and' a half north of t1 1 e . f V'terbo About a mi e d d vicimty o . 1 • • d of a sterile plain of volcanic san an latter town, 11~ the ~I s~ about twenty feet high and five hunashes, a montiCule IS see ' t' 1 composed of concretionary d · · mference en tre Y . . dred yar s m circu . ' t ely thin and thetr mmute . 'l'l lammre are ex rem ' travertm. le . d h t the whole mass has at once undulations are so arrange ' t a This mammillon has . d diated structure. a concentric an :a lime and much of it appears to h~ve been largely quarried for h been formed by a small Jet been removed. It seems to avhe. h continued to rise through . f lcareous water, w IC fl nr fountam o ca . which it gradually raised by ~ver o\;- the mound of traver.tm, s rin of hot water still Issues m ing from the summit. A . P g ed to an open tank, used the neighbourhood, whicdh ~~dconvfey hich as well as the open b l tl bottom an st es o w ' . acso nad uiatt 1w,h icleh conveys t h e wa t er, a re encrusted with travertm. . The country around Rome, like many Campagna dL Roma.- 1 ad referred to, has been at some parts of the Tuscan States a re y lcanic eruptions; and the · d tl e site of numerous vo . . former peno 1 . . t d with lime carbomc acic1' springs are still copiOusly Impr~~a: sprinO' has iately been disand sulphuretted hydroge~. b R~ . l' ~hich deposits alter-d c· 'ta Vecchia y ICCIO I, covere near IVI • ' • d a white aranular rock, not nate beds of a ye~lowish traver~m, an either ino grain, colour, or . . . h bl n hand specimens, distmgms a e, I bl 'There is a passage between 'composition, from statuar~ marT~· ss accumulated near the this and ordinary travertm. . l~ math' ·k * . . 1 C'eS about SIX leet lC • k f spring Is m some P a . . R d Tivoli is the la e o . In the Campagna, between ome an ' . nor Riccioli, whose acquaintance $ I did not visit this spring myself, but. Stg ll known favoured me with an with the geology of· t 1l e envt·~ ons of Rome d1 sf we the spot.' Brocchl·, a ~e w years ·insllection of a 't f ·pec1menll collecte rom . . . d as much BUt e o s . . n with Signor Rtcctoh, au '~ . bl'fore his death, visited the locahty ~~. comp;ar inUmdt~d to Fublish a de~cnptlOn. shuck with the phenomenon, of whtch he OF ThE CAMPAGNA Dl ROMA. the Solfatara, ca1led also Lago di Zolfo, (Jacus albula,) into which flows continual1y a stream of tepid water, from a smaller lake situated a few yards above it. The water is a saturated solution of carbonic acid gas, which escapes from it in such quantities in some parts of its surface, that it has the appearance of being actually in ebullition. " I have found by experiment," says Sir Humphry Davy, " that the water taken from the most t1·anquil part of the lake, even after being agitated and exposed to the air, contained in solution more than its own volume of ca1·bonic acid gas, with a very small quantity of sulphuretted hydrogen. Its high temperature; which is pretty constant at 80° of Fahr., and the quantity of carbonic acid that it contains, render it peculiarly fitted to affo!'d nourishment to vegetable life. The banks of travertin are every where covered with reeds, lichen, confervre, and various kinds of aquatic vegetables; and at the same time that the process of vegetable life is going on, the crysta1lizations of the calcareous matter, which is every where deposited in consequence of the escape of carbonic acid, likewise proceed.-There is; I believe, no place in the world where there is a more striking example of the opposition or contrast of the laws of animate and inanimate nature, of the forces of inorganic che• mica} affinity, and those of the powers of life*." The same observer informs us, that he fixed a stick on ·a mass of travertin covered by the water in May, and in the April following he had some difficulty in breaking, · with a sharppointed hammer, tbe mass which adhered to the stick, and which Was several inches in thickness. The upper part was a mixture of light tufa, and the leaves of confervre: below this was a darker and more solid travertin, containing black and decomposed masses of confervre; in the inferior part, the travertin was more solid, and of a grey colour, but with cavities probably produced by the decomposition of vegetable matter t. The stream which flows out of this lake fi1ls a canal about nine feet broad, and four deep, and is conspicuous in the landscape by a line of vapour which rises from it. It deposits tufa in this channel, and the Tibur probably receives from it, as well as from numerous other streams, much carbonate of lime in so]u• * Consolations in Travel, pp. 123-125._ t Ibid., p. 127,. |