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Show IRON. No'l'E XVIII. f h One of thefe is about fifteen inches in B gentleman o t at town. . n me by Mr. uxton, a . 1 • • I r one and contains beauufuluar- . . d bout fix mc1es m 1ts po a ' . its equatonal diameter, an a . h 1 fpar The other is about eight . . f1: d d. art filled wit ca careous . . . like fep.t ar.t a mcru e . Ia n m p c . 1 ·nits polar diameter, and IS quite d' ter and about JOUr me 1es I inches In ItS equato:ta. lame '• ·k f d'ffierent colours as if a beginning fepa- . b fh ts mternal furface m:u s 0 1 ' · folt.d , utd ekw s onI I r r . ta'•n fifty per cent. of iron, accordlllg Now as theJe leptana con ratiOn ha ta en r ace. 1 . [, . fluid globule by fuhterraneous fire to Dr. Hutton, they would [often or met wto a emt: . I h hole by le(s heat than the limef1:one in their vicinity; and If they were ejdlcdbt uhou.g a t or fiffure would gain a circular motion along wt· t1 1 tlLt el• r progre fufi .v e one lyd t e1dr great heer f 'Cl:ion or adhefion to one fide of the hole. This whirling motion wou pro u.ce onb late fpheroidical form which they poffefs, an d w h't c 11 a.s (a r as .I knohw can[ in o.t 111 anh y other wa !Je accounted for. They would then harden m the atr as t ey :o e mto t e colder !rts of the atmofphere; and as they defcendecl into fo fo~t a matena~ as {hal~ or fuiver, ptheir forms would not be injured in their fall; and the1r prefence m matenals fo di!ft!rent from themfelves becomes accounted for. . . . . About the tropics of the large feptarium above menttoned, are ctrcular emm~nt lmes, {i ch as miaht have been left if it had been coarfely turned in a lath. Thefc lw.es fecm u r.fl of fl 'd matter which feems to have exfuded in circular zones, as their edges to COnilll 0 Ul ' . . ~ I [1 ct' appear blunted or retr.acted; and the fepta.rium feems to have fpl1t eafter m uc 1 e JO.ns .parallel to its equator. Now as the crufi would firf1: begin to cool and harden after tts ejeCtion in a femifluid f1:ate, and the equatorial diameter woul~ become gradually enlarged as it rofe in the air; the internal parts being fo ftcr would il1de beneat~ t~e polar cruf1:, which might crack and permit part of the femifluid to exfudc, and 1t IS pr.obable the aJhefion would thus become lefs in feetions parallel to the equator. Whtch further confirms this idea ofthe produCtion ofthefe curious feptaria. A new-ca!l: canna~ b~Il red-hot with its cruf1: only folid, if it were fhot into the air would prob ab~y burfl: In 1ts paffage; as it would confifl: of a more fluid material than thefe feptana ;. an~ thu~ by difcharging a fhower of liquid iron would produce more dreadful combuf1:wn, tf u.fed in war, th:m could be effeCted by a ball, which had been cooled and was heated agam~ fince in the latter cafe the· ball could not have its internal parts made hotter than -the crufl: of it, without fir!l: lofing its form. J 4-1 NOTE XIX.-FLINT. '1ranfwute to gliltering flints her chalky lands, Orjin.k on O(ean' s bed in countlefs fands.. '. SILICEOUS ROCKS. ·CANTO II. I. 217. THE great maffes of filiceous fand which lie in rocks upon the beds oflime!l:one, or which are f1:ratified with clay, coal, and iron-ore, are evidently produced in the decompofition of \·egetable or anim:tl matters, as explained in the note on moraffes. Hence the imprdTions of ve.getable roots and even whole trees are often found in fand-f1:one, as well as in coals and iron-ore. In thele fand-rocks both the filiceous acid and the calcareous bafe feem to be produced from the materials of the morafs ; for though the prefence of a fil iceom acid and of a calcareous bafe have not yet been feparately exhibitetl -from flints, yet from the analogy of flin~ to fl,wr, and gypfum, and marble, and from the converfion of the latter into flint, there can be little doubt of their cxif1:ence. Th'efc filiceous f.1rKI-rocks are either held together by a filiceous cement, or have :t greater or lefs portion of clay in them, which in fome acts as a cement to the filiceous cry!b.ls, but in others is in fuch great abundance that in burning them they become ai'l imperfect porcelain :tnd are then ufi.;d to repair the roads, as at Cbef1:erfield in Dt:rbyfhire1 thcfe are called argillaceo us grit by Mr. Kirwan. In other p!Jces a calcareous matter cements the cryfl.aJ:, together; and in other places the filiceous cryflals lie in loofe fhatJ. under the marl in the form of white fand; as at Normington about a mile from Derby. The lowef1: beds of filiceous fand-f1:one produced from mora/Ics fcem to obtain their acid from the morafs, and their calcareous bafe from the limefione on which it reHs. Thefe beds polft:fs a filiceous cement, and from their greater purity and harJncfs arc ufed for coarfe grinding-fioncs and fcythe Hones, and are Gtuated on the edges of limefione countries, having lofl: the other il:rata of coals, or clay, or iron, which were originally produced above them. Such arc the fand-rocks incumbent on limefrone near Matlock in Derbyfhire. As thefe fil iceous fand~rocks contain no marine produClions fcattL:rcd amongll: them, they appear to have been elevated, torn to pieces, and many fr::1gments of them fcatt ered over the adjacent country by explofions, from fires within the morafs from which they h.ave been formed; and which diilipated every thing inflammable above and beneath them, except fome f1:ains of iron, with which they are in fome places fpotted. If thefe fand-rocks had been accumulated beneath the fea, and. elevated along with the beds of limefl:one on which they rell, fume veHiges of marin;e fl1ells either in their filiceous or calc:treous fL te mutt have been di!cerned amongH: ,.thcu1. |
