riCINITT of EDINBURGH. 42.5 



I now come, as propofed, to that divifion of the fubject which 

 relates to indurations. By induration is meant, a greater degree 

 of compactnefs, obfervable in particular parts of ftratified rocks, 

 than is ufual throughout their mafs. One part of a bed may be 

 harder than another, confequently more indurated. But the in- 

 duration here alluded to, is that which is fuppofed to have been 

 effected, by an alteration in the denfity of the flone, in confe- 

 qnence of the action of heat. 



These phenomena are of a very ftriking nature, and were 

 firfb brought into notice by Dr Hutton y in them, he found 

 evidence, to him perfectly concluhve, of the igneous formation 

 of whin, and, with that ingenuity and perfeverance which cha- 

 raclerife the whole of his works, he did not fail to generalife 

 his obfervations, and to place the fads, firft noticed in this fpot, 

 in fuch a light, as to render them elTentially ufeful to his 

 theory. 



The anxiety which the difciples of the Wernerian fchool 

 have always evinced, to undervalue the merit of this obferva- 

 tion, is a fure mark of the eftimation in which they hold it ; 

 and it is, therefore, very properly confidered by the fupporters 

 of the oppofite doctrine, as one of their flrongefl holds. In the 

 following lift, are comprehended moil of the varieties, which 

 this indurated fandftone prefents on Salifbury Craig. 



No. 49. is a junction fpecimen *, taken near the fouthern 

 extremity of the Craig ', here the greenftone is of the deep red 

 tinge noticed at No. 17. 



Vol. VI. P. II. 3H No. 



* By junclion fpecimen ia meant, a fpecimen which exhibits the greenftone an«L 

 the fandftone conjoined. 



