Volcanic elafS. 



]70 OBSERVATIONS ON BASALT, &C. 



But, (hough the procefs of arrangement has often only advanced 

 thus far, it has in many inftances proceeded much farther, and 

 it is by no means unufua! to find the entire bafis regularly ar- 

 ranged into cryftalline bodies; thus, lo cite/a well known in- 

 ftance, in many of the ancient lavas of Somma, large augites 

 are imbedded in a cryftalline mats, formed of minute cryftals of 

 ieucite, together with another cryftalline fubftance, whole na- 

 ture is not perfectly determined. 



The cafual occurrence of volcanic glafs i-; iiowife at variance 

 with this account, as it is fufficienllv probable, (hat fome glaffes 

 may have a much greater tendency to cryftalline arrangement 

 than others poffefs; and it cannot appear extraordinary, that 

 regular cryftals fhould fometimes be generated, even in the 

 glafs, as it is a matter of daily occurrence in artificial glaffes, 

 and in furnace flags. 



,. , ,. If the diftinction attempted to be- fiiown between igneous 



Peculiar bodies i » 



maybe afforded fufion and folution be eftabhfhed, it may offer a means of ac- 



by this nrethod C0l intin£ for the abundance of peculiar bodies in lava, which do 

 oi reparation- » . • . i ' , ■ 



not exift in other ntuatmns, or at leaft are of extremely rare 



occurrence. For, if the igneous action decomposes the molecules 

 of the fubftances on which it operates, there feems every 

 probability that new compounds may refult, diffimilar to any 

 fubftances we are acquainted with. It would appear, that the 

 neqeffity of imagining an undifcovered flratum abounding in 

 leucites, chryfolite?, and augites, may be difpenfed with; and, 

 as I have endeavoured (o (how the probability that the mod 

 infufible fubftances will not be the fir ft to cryftallize, the pene- 

 tration of refractory leucites by fuiible augites, will ceafe to be 

 an argument againft both being generated in the lava. I may 

 alio obferve, that the fame eaufes which vary the cryftallized 

 bodies refulting from igneous folution, muft operate upon the 

 unarranged balls ; and that (he fame rock may be fufed in(o 

 lavas extremely diffimilar, as their varieties muft depend on 

 the degree of folution which the fufion has accompliflied.* 

 The facte and If the analogy attempted to be Qiown between the aqueous 



doftrines here and igneous formation appear founded, the tranfition from glafs 



pven will not 



affeft tl e quef- l0 



tiofl of the igne- * 'pj.g ev i^ crce f the generation of leucites in the lava which 

 faraat'wnof^ eontntii them., colle&ed by Leopold de Buch, and Breiflac, and 

 bafalt, finally acquitfeed in by Dolomieu, appears fo fatisfaclory, that it 



can hardly be deemed prefumptuous to affume the point as deter- 

 mined. 



