OBSERVATIONS ON BASALT, &C. 121. 



thofe which confolidated tl%e fluid glafs, and aggregated its 

 particles info a compact uniform (lone.* 



The appearances that I have endeavoured to defcribe, feem Ot^ er con ^"- 

 deferving of confideration in feveral points of view. Few Rem^jye c ; r . 

 things can be more at variance with commonly received opi- cunr >fta»ce, that 

 nion, than the diversified fuccefiion of changes of Aru^^e^^*^^ 

 which this glafs exhibits in its paflage to a cryftallized ftate.idity maybefup- 

 The generation of the globules which unite to form the jafpi- P of "l l ° have 

 deous fubftance, is what we might be prepared to expect, by 

 obferving 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 molecules of the mafs ; yet, immedi- 

 ately after the completion of this arrangement, they receive 

 anew dilpofition, and the radiated fibrous ftru&ure commences. 

 Sometimes this pervades even the unaltered glafs ; but I pre- 

 fume this only to happen where the minute globules firft form- 

 ed were fcattered fo far afunder, that their centres became 

 fibrous, before their peripheries came into contact. This 

 view of the fubjecl is juftified by the analogous operation of 



* The cafe is confiderably different, where cryftals polTeffing re- 

 gular forms are generated in glafs. The molecules of which they 

 are formed, have doubtlefs been only fufpended in the vitreous me- 

 dium; and their union is determined by cryftalline polarity, which 

 appears to me perfectly diftin6l from the fimple aggregation which 

 changes a fluid into a folid, whether it be homogeneous or com- 

 pound, which affe&s the internal arrangement of thofe bodies, but 

 which never can feparate their components into diftincl: maffes, or 

 form them into regular folids. Every molecule, at the moment 

 of its formation, muft neceiTarily be endowed with all the proper- 

 ties it afterwards poflefTes. The fufpenfion of fuch molecules in a 

 fluid medium, though it may conceal, cannot alter thofe proper- 

 ties ; and the union of fuch molecules, to form a regular folid, 

 in no refpect alters their individual or aggregate qualities. Whe- 

 ther heat be evolved at the moment of this union, is a queftion not 

 eafily folved; as the crystallizations with which we are familiar are 

 from chemical folutions, in which fome of the molecules are ge- 

 nerated by the feparation of a combined fubftance, at the moment 

 when others are united by cryftalline polarity. 



the 



