244 THEORY of the EARTH. 



Tented me with the figure of regular flratification ; but, upon 

 examining the whole mafs of rock, I found, that it was only 

 towards the bottom that this ftratified appearance took place ; 

 and that, at the top of the rock, the moft beautiful and regular 

 figure was to be observed ; but a figure the moft oppofite to that 

 of ftratification. It was all compofed of concentric circles ; 

 and thefe appeared to be the fe&ion of a mafs, compofed alto- 

 gether of concentric fpheres, like thofe beautiful fyftems of 

 configuration which agates fo frequently prefent us with in mi- 

 niature. In about eight or ten feet from the top, the circles 

 growing large, were blended together, and gradually loft their 

 regular appearance, until, at a greater depth, they again ap- 

 peared in refemblance of a ftratification. 



THIS regular arrangement of the floating marly fubftance in 

 the body of fait, which is that of the ftrudlure of a coated 

 pebble, or that of concentric fpheres, is altogether inexplicable 

 upon any other fuppofition, than the perfecl fluidity or fufion 

 of the fait, and the attractions and repulfions of the contained 

 fubftances. It is in vain to look, in the operations of folution 

 and evaporation, for that which nothing but perfecl fluidity or 

 fufion can explain. 



THIS example of a mineral fait congealed from a melted 

 ftate, may be confirmed from another which I have from Dr 

 BLACK, who fuggefted it to me. It is an alkaline fait, found 

 in a mineral ftate, and defcribed in the Philofophical Tranfac- 

 tions, anno 1771. But to underftand this fpecimen, fome- 

 tliing muft be premifed with regard to the nature of foflil al- 

 kali. 



THE foflil alkali cryftallizes from a diffblved ftate, in com- 

 bining itfelf with a large portion of the water, in the manner 

 of alum ; and, in this cafe, the water is eflential to the confti- 

 tution of that tranfparent cryftalline body ; for, upon the eva- 

 poration of the water, the tranfparent fait lofes its folidity, and 

 becomes a white powder. If, inftead of being gently dried, 



the 



