FICINlTr of EDINBURGH. 427 



No. 67. In this fpecimen 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 Hutton conceives, that the induration, fo very remark- 

 able in the above fpecimens, was oceafioned by the heat of the 

 whin, when it was injected between the ftrata of fandftone, cau- 

 fing it to undergo a certain degree of fufion ; and, to this idea, 

 the facetted texture of fome of the fpecimens adds considerable 

 weight, fuch arrangements being very familiar in ftones which 

 have undergone fuiion. 



The Wernerian fchool, to account for the fame phenomenon, 

 afTerts, that as fandftone is generally porous, the fluid folution 

 of the trap being introduced into the fiflure, naturally percola- 

 ted to a gTeater or lefs extent *. Again, that it is owing to the 

 intermixture of the matter of the vein, with the rock that forms 

 its walls f ' 7 and, as a proof of this, it is added, that no indu- 

 ration appears, where the traverfed rock is pofTefled 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 contradictory. On Salifbury Craig, and 

 generally throughout the neighbourhood of Edinburgh, where- 

 ever we rind 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. 



3H2 It 



* Comparative View of the Huttonian and Neptunian Theory, p. 13c. 

 t System, of Mineralogy, vol. iii. p. $6$. 



