OBSERVATIONS ON BASALT, &C. J \Q 



There are fome confiderations which appear to offer a par- Explanation of 



tial explanation of the formation of the globules, and of the ^ glomes "and 



radiated fpheroids. It is well afcertained that heat is emitted fpheroids ; from 



by all bodies, in their change from a gafeous to a fluid ftate, * he emi f lon of 

 ...... . ., ... ' heat during con- 



and alio in their change from a fluid to a iolid ftate. It is gelation. 



reafonable to fuppofe, that heat may alio be emitted in thofe 

 changes of arrangement which affect the internal texture of a 

 body, after it has attained an apparently folid ftate. That a 

 fucceffion of fuch changes does actually take place, appears 

 to me demonftrated by the appearances I have defcribed, and 

 by the increafe of fpecific gravity, which feems to keep pace 

 with the internal changes of the fubftance. It would appear, 

 that thefe changes are caufed by a gradual diminution of tem- 

 perature, which permits certain laws to induce peculiar ar- 

 rangements among the particles of the glafs. When feveral of 

 thefe particles enter into this new bond of aflbciation, they 

 rouft form a minute point, from which heat muft iflue in every 

 direction. That heat will gradually propagate itfelf, till the 

 temperature of the glafs is equalized ; and then the recur- 

 rence of the circumftances which induced the flrft particles to 

 arrange, will caufe other particles to arrange alfo, which the 

 attraction of aggregation will difpofe round the point firft 

 formed. A fecond emiflion of heat in every direction will 

 take place; the temperature will again be equalized; and 

 again another concentric coat of arranged particles will apply 

 itfelf to the little globule. But, at the time when the central 

 point of this globule was formed, the equality of temperature, 

 in the mafs of glafs, would probably caufe a number of fimilar 

 points to be generated. The formation of each muft proceed 

 in a fimilar manner to what I have defcribed, till their 

 furfaces touch, and all the glafs be converted into the fame 

 fubftance. 



Thefe globules are therefore formed of concentric coats, General connec- 

 feut they are alfo radiated. Every one muft have remarked d °? b «w«n the 



J J radiated ltruc- 



„.,., , .,„,. . , ,-i,, ture ar> d forma- 



to effect this by chemical folution, the only power to which their t ; on by concen- 



aggregalion yields. It will be evident, from the obfervations that trie coats, 

 follow, that I am inclined to adopt the ingenious idea of Dolomieu, 

 that many apparently homogeneous rocks are compounds of the 

 minute molecules of feveral lpecies of minerals; and that, where 

 a fuitable opportunity is given, thefe will develope themfelves by 

 the formation of their peculiar cryftals, 



the 



