64 lLLUSTkA.TIONS OF THE 



in them are not all of the fame date 



tiid 



all of the fame formation. This is clear 



or 



in the cafe of one vein producing a fhift 

 flip in another ; for the vein which forces the 

 other out of its place, and preferves its own di, 

 redtion, is evidently the more recent of the two 

 and mud have had its materials in a Hate of ac- 

 tivity, when thofe of the other were inert. Some- 

 times, alfo, at the interfedion of two veins, we 

 may trace the current of the materials of the 

 one, acrofs thofe of the other; and here, of 

 confequence, the relative antiquity is determi- 

 ned juil as in the former inftance. 



59. The want of any appearance of ftratifica- 

 tion in mineral veins has already been taken 

 notice of. There is, however, to be obferved, 

 in many inftances, a tendency to a regular ar- 

 rangement of the fubflances contained in them ; 

 thofe of the fame kind forming coats parallel to 

 the fides of the vein, and nearly of an equal thick- 

 nefs. This phenomenon is confidered as one 

 the ftrongeil arguments in favour of the Neptu- 

 nian fyftem, but has nothifig in it, in the leail in- 

 compatible with that theory which afcribes the 

 formation of veins to the adion of fubterraneous 

 heat. When melted matter from the mineral re- I 

 gions was thrown up into the veins, that which 

 was neareft to the fides w^ould foonefl: lofe its heat. 

 The fimilar fubftances, alfo, would unite while 



this 



A. 



