/ 



256 



ILLUSTRATIONS OF THE 



of the ftrata 



a" 



» 1 



' I 



fares in the ilrata were made, at leaft in many 

 inflanees, and the matter poured into them 

 nearly at the fame time, both being effects of 

 the fame caufe, the expanfive force of fiibterra- 

 neous heat. 



229. It is remarked, at § 56., that the fliifting 



is beft obferved where the veins 



make a tianfverfe fedion of beds of rock, con- 

 liderably inclined to the horizon. It is alfo 

 true, that in fome cafes the near approach of 

 the ftrata to the level, may make the ftiifts pro- 

 duced by the veins very eafy to be difcovered. 

 Thus in Derbylhire, where the mineral veins 

 are in fecondary ftrata, nearly horizontal, there 

 is almoft no ihftance in which the correfpond- 



ing ftrata are not obferved to be on different le- 

 vels, on the oppofite fides of the fame vein. 



230. The fa6l defcribed by De Luc, and re- 

 ferred to at § 55., may, for what we know of it, 

 admit of being explained in two ways. The 



great wedge of rock which appears to be infu- 

 lated between two branches of the fame vein, 

 may either be a mafs that has been broken off, 

 and fuftained by the melted matter that flowed 

 all around it ; or, it may be a mafs of rock con- 

 tained between two veins that are in reahty 

 diftind, and of different formation. Whether 

 this laft fuppoiition is the truth, would probably 



evident from a careful examination of both 



parts 



b 



^ 



