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Show 204 MEDALLIONS OF SAN FILIPPO. b t nd sulph ate o f lime ' and sul.p hate containinc:r car ona e a 1 . h l'es the bath falls mto a n Tl ter wuc supp 1 1 . of mac:rnesia. 1e wa d poc::it a solid mass t urty Pond ow here I. t h as b ee n known t.. ,o, eA m~ anufactory of mcc1 a l - ' . t ty yea·rs"". fieet thick, 10 about wen . d t these baths. The water li'ons in basso-rel .I evo I·S carne on a . · 1 p'lts in which 1t deposits 1 into severa ' . is conducted by cana s f sul hate of lime. After bemg thus travertin and crystals o ~ . nveyed by a tube to the . . parts It IS co freed from Its grosser c • ' d ade to fall through a space 11 h mber an m summit of a sma c a ' t 1·s broken in its descent Ly l' t The curren . d of ten or twelve ICe.. which the spray is dispersed ar?un numerous crossed sticks, by bbed lightly over with a upon certa.m mou ld s, whiCh . .a re rfu solid matter h.k e mar bl e I.S d depositiOn o d . h solution of soap, an a '£' 1 st of the fic:rures forme m t e . ld' beauti u ca o . t the result, y1e mg a d . from these expenmen s 1 . t may enve . I mouldt. The ge~ ogts d t t11e hic:rh inclination at wlncl 1. ht rec:rar o o 1! considerab.l e tg 11' ' me proe c1. p1. ta t' ns can be formed ; lOr some IO some semicrysta m . d 1 ost perpendicularly, yet t1 1e f the moulds are dtspose a m o . l ual in all parts. . b deposition IS near y eq b t a foot in thickness, IS o - f stone a ou J A hard stratum o ' F'l' in four months; am, 1 t ·s of San '1 Ippo . I tained from t 1C wa ei f 1 d almost uniform 111 t le . re power u ' an d I as the spnngs a loss to comprehen t le . t we are at no . 1 · quantity given ou ' h. h descends the hill, whtn IS a magnitude of the mass lw Icd 1 tht'r·d of a mile in breadth, , . lenot1 an t1e dfif mile and quarter 10 o 1 . I of two hundred an ty • • 0' a t nc mess . · in some places attammo 1 . . ht have reached, It IS 'f hat lenO't 1 lt mig . f feet at least. o w .o . t oJJ.' like the travertm o . · t re as 1 t 1s c u 11 ' impossible to conJeC u Ii where it terminates abrupt 1Y · San Vignone, by a sma :::~~a:eld in solution is carried on proThe remainder of the rna 1 ders tlJis recent calcareo-mag- But w 1at ren . · 1 bubly to. the sea. f pecu1 ' . t . t to the o·eologtst, IS t le 1ar m c1 es b . nesian hmestone 0 . . ~ m~rinO' so strikmg an ana-spheroidal forms wln~h It ~~:u::"~e~tric s~ructure displayed in logy, on the one han ' to f 1 cade of Tivoli, and, on the the calcareous trave~ tm' 0 t 1e cf ast h·e English magnesi·a n 1t' me· other, to the sphermdal £Borms o this latter and many of the stone of Sunderland. etween * ltl' Ell Plu.l . Jo urn., v • 2' p. 292. pr, Grosse, on the Baths of San. 1 lppzo97 . · t lbul., P· • BI'IIEROIDAL STRUCTURE. 2oo appearances exhibited at San Filippo, and several other recent deposits of the same kind in Italy, there is every feature of resemblance; the same combination of concentric and radiated structure, with small undulations in each concentric ring, occasional interferences of one circle with another, and a small globular structure subordinate to the large spheroidal, with frequent examples of laminre passing off from the external coating of a spheroid into layers parallel to the general plane of stratification. There are also cellular cavities and vacuities in the rock, constituting what has been termed a honeycombed texture. The lamination of some of the concentric masses of San Filippo is so minute, that sixty may be counted in the thickness of an inch. Yet, notwithstanding these marks of gradual and successive deposition, the symmetry and magnitude of many of the spheroidal forms might convey the idea, that the whole was the result of chemical action, simultaneously operating on a great mass of matter. The concretionary forms of our magnesian limestone have been supposed by some to have been superinduced after the component parts of the rock had been brought together in stratiform masses; but a careful comparison of those older rocks with the numerous travertins now in progress of formation in Italy, leads the observer to a different conclusion. Such a structure seems to be the result of gradual precipitation, and not of subsequent re-arrangement of the particles'll:. Each minute particle of foreign matter, a reed, or the fragment of a shell, forms a nucleus, around which accessions of new Jaminre are formed, until spheroids and elongated cones, from a few inches to several feet in diameter, are produced; for, as the precipitate is arranged uy the force of chemical affinity, and not of t.< The structure of the English magnesian limestone has been described, in an elaborate and profound paper on that formation, by Professor Sedgwick. Geol. 'l'rans., vol. 3, second series, part i., p. 37. Examples of almost all the modifications of concretionary arrangement, together with the brecciated and honeycombed structure to which he alluues, may be found either in the deposits of travcrtin springs in various parts of Italy, or in the subaqueous travertins of Auvergue and Sicily,-the former of lacustrine, the latter of submarine origin. These will be alluded to in their proper places, awl I shall merely observe here, that, after examining these more recent deposits, I visited Sunderland, and recognized a degree of identity in the. various and complicated forms there assumed by the magnesian limestone, which sahsfiecl me that the circumstances undt'r which they were formed must have been perfectly analagou~ to those under which the mineral springs of volcanic countries are now giving birth to calcareous1 calcareo-magnesian, and ca.lcareo-siliceous rocks. |
