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Show QYPSEOUS AND StLtCE<H.TS SPRINGS. 212 . . d te concepti.o n of the chanO0' eS now m phro - causes of our ma equa I 1 ften been supposed, t at gt·ess on t l Je ear tl 1 , s s urface · t 1l'a s • 0 tlJe Indian and Pact'f i c f tl oral rCCIS In . • the greater part 0 Je be . lcanos -which seems mdt-b d su marme vo ' oceans were ase on l fi·equently assumed by them ; h · lar s Jape so . cated by t e cir·cnu nt 1·n favour of th1s theory t onger arO'ume but perhaps a sti s r 1 b t abundance of carbonate of might be .deduced from at~~ g:~~th of zoophytic and shelly lime reqmred for the r P gh' ·h could only be looked for b ndance w 1c limestones,-an a u 1 nd frequent earthquakes, as 1 . tive vo canos a where t Jere a.r e1 ac f the Sou t l1 p aci'f ie . We may confident 1y amongst the Is es o f ni'c life would be promoted l d 1 pment o orga infer, that t 1e eve 0 mollusca by the heat, car-nd testaceous ' in corals, sponges,. a d th mi'neral ingredients in a state · 'd 1' ihca an o er home ac.1 , tm· e, s t b' y su b marm. e sprinDo" s ' in the same manner of solutwn, g1v~n °~ . l d in the lake of the Solfatara, as the vegetation IS qmc {ene d 'b d in the Campagna d1. R oma, before escn e • . All other mineral ingredients where- Gypseous .~prmgs.- . . O'nated arc insignificant in · · ral are 1mp1 eo ' with sprmgs m ge~e 1' and this earth is most ft·e· q · · mpar1son to 1me, · 'd - uantity m bc'o d I. lh carb om.c acl' d . But as sulphul'.l c ac1 quently com me w er frequently supphed by and sulphuretted hydrogcnl atrc vps!m is now deposited .largely . must presume t Ja gy . . h sprmgs, we l l The gypseous preCipitates, owever, in many seas and a {es. to be confined to a very hitherto known on the lBandd, appeaar~ Vl' enna which feed the . Tl at a en, ne ' l few spnngs. Jose 1es Some of these supp y, public bath, may be cite1 as exam~ho~sand cubic feet of water singly, from six hun~re to one d . composed of a mixture d ] ostt a fine pow er' per hour, an .c ep . 1 1 hur and muriate of lime*· of sulphate of hme, wlt 1 suP SILICEOUS SPRINGS. er should hold a very large Azores.-In order .th.at ~at , necessary that it should .1. · lutwn 1t seems . quantity of Sl ICa ~n so ' . t. and as it may retam a be raised to a hlgh temperatUI e f' the sea than in the atmo-greater heat und er the pressure o h d 1 be more c arge sphere, submarine sprm· gs rna y per1aps . . h si uc uu Bassin ue Vienne, P· 10. P t Essai sur la Conshtuhon p Y· q 229 • revos ,, . t Daubeny, on Volcanos, P· ... GEYSERS OF ICELAND. 213 with silex than any to which we -have access. The hot springs of the Valle das Furnas, in the Island of St. Michael, rising through volcanic rocks, precipitate vast quantities of sili. ceous sinter, as it is usually termed. Around the circular basin of the largest spring, called " the Caldeira,'' which is between twenty and thirty feet in diameter, alternate layers are seen of a coarser variety of sinter mixed with clay, including grass, ferns, and reeds, in different states of petrifaction. Wherever the water has flowed, sinter is found rising in some places eight or ten inches above the ordinary level of the stream. 'l'he herbage and leaves, more or less incrusted with silex, exhibit all the successive steps of petrifaction, from the soft state to a complete conversion into stone; but, in some instances, alumina, which is likewise deposited from the hot waters, is the mineralizing material. Branches of the same ferns which now flourish in the island, are found completely petrified, preserving the same appearance as when vegetating, except that they acquire an ash-grey colour. Fragments of wood, and one entire bed from three to five feet in depth, composed of reeds now common in the island, have become completely mineralized. The most abundant variety of siliceous sinter occurs in layers from a quarter to half an inch in thickness, accumulated on each other often to the height of a foot and upwards, and constituting parallel, and for the most part horizontal, strata many yards in extent. 'rhis sinter has often a beautiful semi-opalescent lustre. One of the varieties differs from that of Iceland and Ischia in the larger proportion of water it contains, and in the absence of alumina and lime. A recent bt·eccia is also in the act of forming, composed of obsidian, pumice, and scm·ire, cemented by siliceous sinter*. Ge1.jSers of Iceland.-But the hot springs in various parts of Iceland, particularly the celebrated geysers, afford the most remarkable example of the deposition of silex. '!'he circular reservoirs into which the geysers fall, are filled in the middle with a variety of opal, and round the edges with sinter. The plants, encrusted with the latter substance, have much the same appearance as those encrusted with calcareous tufa in our own * Dr. Webster, on the Hot Sr1rings of Furnas~ Ed. Phil. Journ. 1 vol. vi., p. 306. |