84 OBSERVATIONS 
is true indeed that there are many of thefe angles obtufe; but 
there are an equal number, which are as much lefs than the 
right-angle, as the others are greater. ° 
In whichfoever of thefe two lights we are to take the explana- 
tion of this mineral appearance, my argument, viz. that thefe 
two fubftances had concreted together from a fluid ftate of fu- 
fion, is equally fupported. For whether cryftalizing quartz 
fhall inclofe a body of feld-fpar, or concreting feld-fpar deter- 
mine the fhape of fluid quartz ; particularly, if we have, as is 
here alfo the cafe, two folid bodies mutually including and in- 
cluded by each other, it amounts to a demonftration, that thofe 
bodies had concreted from the fluid ftate of fufion, and had 
not cryftalized in the manner of falts from a folution. There- 
fore, here is the teftimony of granite from three different places 
of the earth, vz. from the Daouri, from the Oural Mountains, 
and from Scotland, by which this truth is manifefted. 
Ir would feem that the circumftances, neceflarily concurring 
in order to produce this particular effect, are rarely to be found ; 
and the external circumftances which attend it in the eaft, do 
not appear to accompany it in the weft of Europe. In Scot- 
land, this {tone neither forms the walls of a vein, nor are to- 
pazes found connected with it, as M. Parrin found it in the 
eaft. The internal circumftances, therefore, which, in the 
mafs of granite, determine this particular conftruction of the 
ftone, are to us unknown. 
Ir is not, however, confined to any particular place or fituation ; 
it is found both at the level of the fea, and upon the higheft parts. 
of the earth, and in countries extremely diftant from each other. 
Now, confidering that nothing is more general in minerals than 
granite, it is furprifing that this particular modification of its. 
conftituent parts has been fo little obferved. But, as it would. 
feem to take place only in fmall portions of the granite mafs, 
there may be fimilar examples in many mafles, or in moft gra- 
nite 
