VICINITY of EDINBURGH. 427 
No. 67. In this {pecimen there is fomething very like the ap- 
pearance of an agate ; it, however, is not contained in the fub- 
ftance of the greenftone, but in the ftratified matter below it. 
No. 68. Another fpecimen of the fandftone, in its unaltered 
ftate, taken about thirty feet from the greenftone. 
Dr Hurron conceives, that the duration, fo very remark- 
able in the above fpecimens, was occafioned by the heat of the 
whin, when it was injected between the ftrata of fand{tone, cau- 
fing it to undergo a certain degree of fufion; and, to this idea, 
the facetted texture of fome of the fpecimens adds confiderable 
weight, fuch arrangements being very familiar in ftones which 
have undergone fufion. 
Tue Wernerian {chool, to account for the fathe phenomenon, 
afferts, that as fandftone is generally porous, the fluid folution 
of the trap being introduced into the fiffure, naturally percola- 
ted to a greater or lefs extent *. Again, that it is owing to the 
intermixture of the matter of the vein, with the rock that forms 
its walls +; and, as a proof of this, it is added, that no indu- 
ration appears, where the traverfed rock is poffefled of a quart- 
zy bafe. 
THEsE arguments occur in different works, but they appear 
to me very little calculated to fupport the point in difpute, 
if not in fome refpects contradi@tory. On Salifbury Craig, and 
generally throughout the neighbourhood of Edinburgh, where- 
ever we find fandftone coming in contact with greenftone, 
either in beds or veins, we are almoft certain, that an indura- 
tion will be exhibited along the edge of the ftrata. 
ER 2 It 
“ Comparative View of the Huttonian and Neptunian Theory, p. 13¢.. 
+ System of Mineralogy, vol. iii. p. 365. 
