1474 EFFECTS of HEAT 
fubftance, which, in this fluggifh ftate, would be little difpofed 
to move, being confined in its original fituation by contiguous 
beds of more refractory matter, would cryftallize, without 
undergoing any change of place, and conftitute one of thofe 
beds of whinftone, which frequently occur interftratified with 
fandftone and limeftone. 
In other cafes where the heat was more intenfe, the beds of 
fand, approaching more nearly to a ftate of fufion, would ac- 
quire fuch tenacity and toughnefs, as to allow themfelves to be 
bent and contorted, without laceration or fracture, by the in- 
fluence of local motions, and might affume the fhape and’ 
character of primary {chiftus: the limeftone would be highly 
cryftallized, and would become marble, or, entering into thin 
fufion, would penetrate the minuteft rents in the form of cal- 
careous fpar. Laftly, when the heat was higher ftill, the fand 
itfelf would be entirely melted, and might be converted, by the 
fubfequent effects of flow cooling, into granite, fienite, &c. ; 
in fome cafes, retaining traces of its original ftratification, 
and conftituting gneifs and ftratified granite ; in others, flowing 
into the crevices, and forming veins of perfect granite. 
In confequence of the action of heat, upon fo great a quan- 
tity of matter, thus brought into a fluid or femifluid ftate, and 
in which, notwithftanding the great preflure, fome fubftances 
would be volatilized, a powerful heaving of the fuperincumbent 
mafs muft have taken place; which, by repeated efforts, fuc- 
ceeding 
cryftals of ice, like the blade of a knife, formed ina mafs of clay, of fuch ftiffnefs, 
that it had juft been ufed to make cups for chemical purpofes. In many of 
my former experiments, I found that a fragment of glafs made from whinftone or 
lava, when placed in a muffle heated to the melting point of filver, affumed a 
cryftalline arrangement, and underwent a complete change of character. During 
this change, it became foft, fo as to yield to the touch of an iron rod; yet retained 
{uch ftiffnefs, that, lying untouched in the muffle, it preferved its fhape entirely ; 
the harp angles of its fraéture not being in the leaft blunted. 
laa 
