HUTTONIAN THEORY. 



39 



m 



his 



It 



i 



?i 



9 



were round fo many different centres of attraction 

 is alfo an appearance quite inconfiftent with the 

 notion of depofition ; both thefe, however, are 

 compatible with the notion of folidity acquired by 

 the refrigeration of a fluid, where tlie whole mafs 

 is aded on at the fame time, and where no fol- 

 vent remains to be difpofed of after the indura- 

 tion of the reft. 



35. Another fpecies of foffil-falt exhibits ap- 

 pearances equally favourable to the theory of 

 igneous confolidation. This is the trona of A- 

 frica, which is no other than foda, or mineral al- 

 kali, in a particular ftate. Thefpecimen of this 

 foffil in Dr Black's, now Dr Hope's, collection, 

 is of a fparry and radiated ftrudure, and is evi- 

 dently part of the contents of a vein, having a 

 ftony cruft adhering to it, on one fide, with its 

 own fparry ftrudure complete, on the oppofite. 

 It contains but about one-fixth of the water of 

 cryftallization effential to this fait when obtain- 



/ 



ed in the humid way ; and, what is particularly 

 to be remarked, it does not lofe this water, nor 

 :ome covered with a powder, like the com- 

 n alkali, by fimple expofure to the air. It is 

 dent, therefore, that this folTil does not origi- 



be 



nate from mer 



precipitation 



il 



add, that in its fparry ftrud: 

 dent marks of having once 



C4 



id when we 

 contains evi- 



been fluid 



have 

 little 



•^ 



