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Show 210 TRAVERTIN OF TIVOLI, ETC. of havm. O' b een suspemled, without sulp' port, has the appearantciell. t became0 a sp h er oi'cl'a l mass of great t tmen-in. the w'la"the r, unt ion obtam. e d of tl les e deposits ' about four hun-s10ns. e sec . 1 d r the temples of Vesta and the 1 • k · nmedmte y un e . . · dred feet t 11c 'u h . 'd 1 ich arc from stx to etyht feet tn Sibyl, displays some sp ,.e1 ~1 s .~;ing about the eighth of an inch diameter, each ~oncentnc ~~~~ ram exhibits about fourteen feet in thickness. 'I he annexe 1 ~g tile path cut out of the rock in · i mass as seen m . . of this tnmense ' l f Vesta to the Grotto d1 Nettuno*. descending from t!1e tern~~ 0 5) are of hard travertin and soft The beds (eta, diagra~ ~·~·(b) Lthe o·lobllles being of different tufa; below them is a ~ISO 1 e . 'a m~ss of concretionary tra- . d . th thts appears sizes. ; (u n ) e1 nema e of t h e spl 1er.o i ds being of the above-me. n-vertm cc , so. . I orne places (as at d), there Is a tioned extl'aordmm·y. stze. n ~ tu"a surrounded by concentric f . 1 us hmestone, or 1 ' • . mass o aAm mtph e1 0b ottom I•S ano th er. bed of ·p is· olite (b), m which layers. t b t the size and shape of beans, and the small nodules are a o~ t . ·I. xed with some smaller oolitic f h f filberts, m et m · some o t em 0 · I the tufaceous s t t .a t·, t, wood is seen converted m. to af ~rams. n I . robable that the date of the greater portwn.o hght tufa. tIs P . be anterior to the era of his-this calcareous formatiOn lm~y a great cascade at Tivoli .L' know that t 1c1 e was . ~ory, lOr w_e . . but in the upper part of the trave~·tm, m very anCient times ' f b 1 eel in which the outer circle is shewn the hollow le t yd a w 1 ' d and the spaces which l 1 e been ecompose , . and the spo <es 1av l f 'd It seems impossible to explam they fill~~ have be~n c t ~~1 '~ithout supposing that the wheel the positiOn of tlus mou ' . d . dd d b £ the lake was drame . was Imbc e e ore . t enter into minute de· l. · d not permit us o . 'f Our lmlt. s tol an.o us li.m estones t o hich sprinO's ll1 di. w tl • tails respectt~g le v . 1 ivin birth. Pallas, in Ills ferent countnes are contmual y g g biect from time 1 h C· ucasus a country now su J ' journey a ong t e ad fi ' d b violent earthquakes, enu- . b n t an ssure J . d to time, to e re . hich have deposite mon-merates a great many hot .sprmgs, lw in composition and ticules of travertin preCisely ana ogous . this drawm. g, tho m· num erable l.h iu • 1 have not attempted to express, 1~ . ed but tho Jiues given layers of which these magn~fi~ent .spherOI~s ~: c:r:~~;ar~ted by minute varin· roark some of the natural divlslons l~to whl•crhh yd I tions also are much smaller, f th 1 mmoo e un u a tions in the size or colour o . e ! . th is expressed in the diagram. in prol1ortion to the whole clrcumlerence, . an ., CALCAREOUS TUFA. 211 structure to those of the ·baths of San Filippo, and other localities in Italy. When speaking of the tophus-stone, as he terms these limestones, he often observes that it is snow-wltite, a description which is very applicable to the newer part of the deposit at San Filippo, where it has not become darkened by weathering: In many localities in the regions between the Caspian and Black seas, where subterranean convulsions are frequent, travellers mention calc-sinter as an abundant product of hot springs. Near the shores of the Lake Urmia (or Maragha), for example, a marble is rapidly deposited from a thermal spring, which is much used in ornamental architecture "'f. We might mention springs of the same kind in Calabria and Sicily, and indeed in almost al1 regions of volcanos and earthquakes which have been carefully investigated. In the limestone districts of England, as on Ingleborough llill, in Yorkshire, we often see walls entirely constructed of calcareous tufa, enclosing tenestria] shells and vegetables, and similar tufa still continues to be formed in that district. 'rhe growth of stalactites, also, and stalagmites in caverns and grottos, is another familiar example of calcareous precipitates. 'l'o the solvent power of water, surcharged with carbonic acid, and percolating various winding rents and :fissures, we may ascribe those innumerable subterranean cavities and winding passages which traverse the limestone in our own and many other countries. In the marshes of the great plains of Hungary, horizontal beds of travertin, including recent fresh- water shells, are continually deposited, and are sufficiently solid to serve for building- stones, all the houses of Czeled being constructed of this material t. To analogous deposits in the Jakes of Forfarshire, in Scotland, we shall refer more particularly when speaking of the imbedding of plants and animals in recent deposits. The quantity of calcareous rock which results from mineral waters in volcanic regions, conspicuous as it is, must be considered as insignificant, in comparison to that which is conveyed by rivers to the sea ; and our inability to observe subaqueous accumulations resulting from this source, is one of many • Hoff, Geschichte, &c., vol. ii., p. 114. t Beu<lant, Voyage en Hongrio, tom, ii., p. 353. P2 |
