TRANSITION GREENSTONE OF FASSNEY. I27 



posable, favourable to vegetation, and no where 

 visible except in the beds of rivulets. 



In the bed of the rivulet south of Herd's Hill, 

 there occurs an alternation of very thick beds * of 

 Grey-wacke and Grey-wacke-slate. These beds 

 are stratified : their direction corresponds with 

 that of the mountain range, which runs nearly 

 north-north- east, and south-south-west. The dip 

 is north-westerly, and the angle of inclination 

 about 6o°. The beds of grey-wacke-slate are the 

 most considerable in thickness, and I understand, 

 have been worked to some extent, for roofing, by 

 Mr Knox, but without much success. 



Following the course of the water, I came upon 

 a curious porphyrinic rock, having a basis of com- 

 pact felspar, approaching to claystone, with nu- 

 merous small imbedded crystals of quartz, and a 

 few of felspar. This stone has a striking resem- 

 blance to one of the members of the overlying 

 porphyry formation ; but as we have only an op- 

 portunity of examining a very small portion of the 

 bed, it is difficult to say, whether it is Felspar 

 Porphyry, a variety of Compact Felspar, or of 

 Claystone. This bed is six or eight feet thick, is 

 conformable with the strata of Grey- Wacke, and 

 must therefore be regarded as of the same forma- 

 tion. Another bed of this rock, but thinner, is 

 met with a little to the westward, with strata of 

 grey-wacke intervening. 



