ROWLEY RAG. 



effefted by a gradual tranfition, the limits of which cannot 

 be affigned ; but more generally by the formation of fe- 

 condary fpheroids, in the heart of the compact jafpideous 

 fubftance. Thefe fpheroids differ edentially from thofe firlt 

 defcribed : the centres of their formation are more remote 

 from each other, and their magnitude is proportionably 

 greater, fometimes extending to a diameter of two inches, 

 and feeming only to be limited by contaft with the peri- 

 pheries of other fpheroids. They are radiated with diltin6t 

 fibres : fometimes the fibres refemble thofe of brown haema- 

 tites, and fometimes they are fafciculated irregularly, fo as 

 to be very fimilar in appearance to the argillaceous iron ores, 

 rendered prifmatic by torrefaftion. They are generally 

 well defined, and eafily feparable from the mafs they are en- 

 gaged in ; and often the fibres divide at equal diftances from 

 the centre, fo as to detach portions of the fpheroid in con- 

 centric coats. The tranfverfe frafture of the fibres is corn- 

 pad and fine-grained ; the colour black ; and the hardnefs 

 fomewhat inferior to that of the bafaltic glafs. When two 

 of the fpheroids come in contaft by mutual enlargement, no 

 intermixture of their fibres feems to take place : they appear 

 equally impenetrable ; and as neither can penetrate, both 

 are compreffed, and their limits are defined by a plane, at 

 which a feparation readily takes place, and each of the fides 

 is inveited with a ruity colour. When feveral fpheroids 

 come in contaft on the fame level, they are formed by 

 mutual preflure into pretty regular prifms, whofe divifion is 

 perfeftly defined ; and when a fpheroid is furrounded on 

 all fides by others, it is comprefied into an irregular poly- 

 hedron. 



The tranfition from this fibrous ftate to a different arrange- 

 ment, feems to be very rapid, for the centre of molt of the 

 fpheroids becomes compaft before they attain the diameter 

 of half an inch. As the fibrous itrufture propagates itfelf 

 by radiating into the unarranged mafs, the compaft nucleus, 

 which fupplies its place, gradually extends till it finally attains 

 the limits of the fpheroids ; and the fame arrangement per- 

 vades the matter comprehended between them. The mafs 

 has now affumed a compaft ftony texture, and poflefies 

 great tenacity. Its hardnefs is fomewhat inferior to that of 

 the glafs from which it was formed. Its attion on the mag- 

 netic needle is very confiderable. Its fpecific gravity is 

 2.938. Its colour is black, inclining to iteel grey ; it is 

 abfolutely opaque, and only reflefts light from a few minute 

 points. Though the divifions between the fpheroids are 

 rendered imperceptible to the eye, they are not obliterated, 

 and their rufty furfaces are often difclofed by an attempt to 

 frafture the mafs. 



A continuation of the temperature favourable to arrange- 

 ment fpeedily induces another change. The texture of the 

 mafs becomes more granular, its colour rather more grey, 

 and the brilliant points larger and more numerous ; nor is it 

 long before thefe brilliant particles arrange themielves into 

 regular forms ; and finally the whole mafs becomes pervaded 

 by thin cryftalline lamina;, which interfeft it in every 

 direftion, and form projefting cryftals in the cavities. The 

 hardnefs of the bafis feems to continue nearly the fame ; but 

 the aggregate aftion of the bafis and of the imbedded cryftals 

 on the magnetic needle, is prodigioufly increafed. It appears 

 to poflefs fome polarity, and minute fragments are fufpended 

 by a magnet. Its fpecific gravity is fomewhat increafed, as 

 it is now 2.949. The cryftals contained in it, when examined 

 by a microfcope, appear to be fafeicul'i of flender prifms, 

 nearly rectangular, terminated by planes perpendicular to 

 the axis ; they are extremely brilliant, but their colour is 

 greeniih black ; they are harder than glafs, and fufible by 

 the blowpipe ; they are fufpended by the aftion of a magnet. 



9 



They are arranged nearly fide by fide, but Hot accumulated 

 in thicknefs, fo that they prefent the appearance of broad 

 thin laminae ; they crofs one another at all angles, but always 

 on nearly the fame plane ; and the lamiiue thus formed are 

 often three or four lines long, and from a line to a line and 

 a half broad, but extremely thin. 



It feems obvious that an equalized temperature would have 

 rendered the whole fimilar to the fubftance laft defcribed ; 

 and it may be fairly inferred, that by a continuance of heat 

 the minute cryftals would have been augmented in their 

 dimenfions by the acceffion of fimilar particles ft ill engaged 

 in the bafis, or by the union of feveral cryftals, till they ac- 

 quired fufficient magnitude for their nature to be abiolutelv 

 determined by the ufual modes of inveftigation. It is 

 poffible, however, if fuch precautions had been taken as 

 might have fecured this degree of perJjftion in the ulterior 

 refult, that the mafs would only have exhibited an uniform 

 afpeft, and that the interefting initial phenomena would not 

 have been difcovered. 



The appearances here defcribed feem defeiving of con- 

 fideration in feveral points of view. Few things can be 

 more at variance with commonly received opinion, than the 

 diverfified fucceffion of changes of itrufture which this glafs 

 exhibits in its paflage to a cryftallized ftate. The gene- 

 ration of the globules which unite to form the jafpideous 

 fubftance, is what we might be prepared to expeft by ob- 

 ferving the cooling of a common iron furnace flag. But it 

 appears not very obvious to common apprehenfion that the 

 fpecies of arrangement requifite to form this intermediary 

 fubftance, could be compatible with any fluidity permitting 

 farther motion of the ultimate particles of the mafs ; yet 

 immediately after the completion of this arrangement, they 

 receive a new difpofition, and the radiated fibrous itrufture 

 commences. Sometimes this pervades even the unaltered 

 glafs ; but Mr. Watt prefumes this only to happen where the 

 minute globules firlt formed were icattered fo far afunder that 

 their centres became fibrous before their peripheries came into 

 contaft. This view of the fubjeft is jultilied by the ana- 

 logous operation of the formation of cryftals fimilar to thofe 

 defcribed in the heart of the radiated fpheroids, while their 

 exterior ftill retained the fibrous texture. 



If it be confidered as extraordinary that a change fhould 

 be effefted, converting an apparently fohd and homogeneous 

 mafs into an accumulation of radiated fpheroids, and that 

 thefe radii fhould lofe their fibrous itrufture, and affume the 

 texture, afpeft, and tenacity, of a compaft, hard, and ho- 

 mogenous ftone, it is certainly much more extraordinary 

 that this ftone fhould permit farther arrangement to proceed, 

 and fhould enable the cryftalline molecules which it contains 

 in a ftate of confuted aggregation, to arrange themielves, 

 and to form regular cryftals, which, although minute, are 

 equal, in the perfeftion of their forms, and in the brilliancy of 

 their natural polilh, to the moil precious products of cryf- 

 tallization. It is alfo well deferving of obfervation by how 

 regular a march the magnetic influence of the fubftance 

 keeps pace with the perfeftion of its arrangement, till it 

 becomes fo powerful that fragments of the regenerated ftone 

 are fufpended by the magnet. 



It has been moll juftly remarked by Mr. Smithfon, that 

 folution, far from being neceffary to cryltallization, effectually 

 prevents its commencement ; for while folution fubfifts, 

 cryltallization cannot take place. It may remain a queition 

 whether previous folution be effential as a preparatory means 

 of obtaining, by fubfequent evaporation or cooling, the 

 fmall pans of bodies difengaged, fo that they may unite 

 to form regular cryftals. If, by folution be only meant 

 that fimple aftion of heat, or water, which merely coun- 

 teracts 



