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Show 200 CALCAREOUS SPRINGS. interior. But as the geographical limits of mineral waters are not confined to volcanic regions, being coextensive with the whole globe, as far as is hitherto known, we must consider them apart, and in their connexion with rivers rather than volcanos. 'Ve might divide the consideration of springs, like that of rivers, into their destroying and reproductive agency; but the former class of effects being chiefly subterranean, are beyond the reach of our observation; while their reproductive power consists chiefly in augmenting the quantity of matter deposited by rivers in deltas, or at the bottom of the sea. We shall, therefore, arrange the facts of geological interest, respecting mineral springs, under the head of the different ingredients which predominate in their waters. CALCAREOUS SPRINGS. OuR first attention is naturally directed to springs which are highly charged with. calcareous matter; for these produce a variety of phenomena of much interest to the geologist. It is well known that rain-water has the property of dissolving the calcareous rocks over which it flows, and by these means, matter is often supplied for the earthy secretions of testacea, and certain plants on which they feed, in the smallest ponds and rivulets. Hut many springs hold so much carbonic acid in solution, that they are enabled to dissolve a much larger quantity of calcareous matter than rain-water; and when the acid is dissipated in the atmosphere, the mineral ingredients are slowly thrown down in the form of tufa or travertin. Calcareous springs, although most abundant in limestone districts, are by no means confined to them, but flow out indiscriminately from all rock formations. In Central France, a district where the primary rocks are unusually destitute of limestone, springs copiously charged with carbonate of lime rise up through the granite and gneiss. Some of these are thermal, and probably derive their origin from the deep source of volcanic heat, once so active in that region. One of these springs, at the northern base of the hill upon which Clermont is built, issues from volcanic peperino, which rests on granite. It has formed, by its incrustations, an elevated mound of solid travertin, or calc-sinter, as it s sometimes called, two hundred and forty feet in length, and, at its termination, sixteen feet high, and twelve wide. An· TUSCAN TRAVERTIN . . . 201 other mcrustmg spring . I Ch 1 m t le same d t . a uzet, near Pont G"l d . . epar ment, Situated at .l' I >au , nses In · 10ot of a reO'u]ar volcani· a gneiss country at the 0 c cone at 1 t . ' calcareous rock. Some . ' eas twenty miles from any b I . . masses of tufaceo d . y t us sprmo-, have an o I't' us eposit, produced o 0 I IC texture. Valley oftlte Elsa -If F · we pass from th 1 . . ranee to that ~hich skirts the A enn. ~ vo came ?Istrict of sula, we meet with innumerabl ~ mcs .m the Italian peninso much calcareous matter tl e sphrmgs, whiCh have precipitated f T . ' Hlt t e whole d · o uscany IS coated over with . . groun m some parts beneath the foot. ttavertm, and sounds hollow In other places in the same countr descending the slantino- sid f I "11 y' compact rocks are seen f I o es o u s ver h . o ava-currents, except th t h ' y muc m the manner terminate abruptly wh ah t ey are of a white colour and These consist of the c len t ey reach the course of a ;.iver I . a careous preci . t f . . t le?I still flowing, while others h PI ~teo sprmgs, some of their position. Such ma~s fave disappeared or changed I'll I . ~ es are reque t h 11 s w 1Ich bound the v 11 f n on t e slope of the of the Arno, which fiowas ~~a~ ~h~ EI~a, one of the tributaries h~n?red feet deep, shaped out o; e, t lrou?h a valley several tammg fossil shells of . . a lacustrme formation con £ existmg spe · TI ' - ormable to the lacustrine beds c;~· . l.e travertin is uncon-the slope of the sides of the v~I~: :'f.<Its mclmation accords with other small rivulets which .l' d I y . The Sena, and several Ia p i'd "f · Jee t 1e Els h I. ymg wood and herbs . d . a, ave the property of aquatic plants, such as char~ an ·h· I~ t~e bed of the Elsa itself, carb~nate of Jime, are ver ain~ln Ic a sorb large quantities of seen m the same valley buybbl' dant. Carbonic acid is also no prec·i p·i tate of tuf: ' . b lllOo' up fro1 n many springs wh t I I a Is o servabl 'T . ' ere raves las mentioned e. argwni, who in h' T a great nu b f . Is uscany, found no d'Lr m er o mmeral wate. . th Iuerence b t I 1s m ermal springs Th . e ween t le deposits of c ld d · · ey Issue · o an nme limestone sh 1 d sometimes fi"Om the old A the fl ' a e' an sandsto h · . er pen-y ow from more modern d .ne, w Ile, In other places case ' tl lei· r source eposits '· b u t ' even m. th 1 ' series of strata. may probably be in, or below th: ~~;r •o r ne of the finest e Caldane, near Col! e. xamples of tbese whicb I snw, wns at tbe M li 0 no delle |
