i 



MINERALOGY OF THE REDHEAD. 561 



tht roads, and these mark the boundaries of the 

 two rocks. 



Where the sandstone-rocks terminate, they are 

 seen to rest upon a bed of por^phyry-congloinerate. 

 When this rock is fresh and untarnished by the 

 weather, it presents a uniform surface ; but where 

 it is beginning to decompose, its angular frag- 

 ments become visible. These are somewhat blunt 

 in the edges, and generally pass imperceptibly in- 

 to the basis in which they are imbedded, although 

 at times, these pieces have a smooth surface on one 

 or two sides, as if a little worn by attrition, while 

 at the other extremity, they blend wath the gene- 

 ral mass. The whole bed is composed of the 

 same kind of rock, — a claystone, with numerous 

 crystals of earthy felspar. This bed is upwards 

 of twenty feet in thickness, and rests upon a bed 

 of slaty- sandstone-conglomerate, or a sandstone in 

 apparent fragments, imbedded in a basis of a si- 

 milar composition, and possessed of a slaty frac- 

 ture. The pavemient of this sandstone, would 

 have been invisible, had not a slip taken place, 

 by which the strata are better exposed, and the 

 sandstone is seen to rest upon a bed of porphyry- 

 conglomerate, precisely similar to that which 

 forms its roof. To this last bed of porphyry, 

 succeed strata of amygdaloid, in many places pass- 

 ing into trap-tuff. 



The amygdaloid varies much in its composition. 

 The basis in some cases, appears to be wacke, in 



Aa3 



