8 DESCRIPTION of the 



tinue their direction upwards, decreafing in their diameters as 

 they afcend, until they nnifh their courfe near to the fuperficial 

 foil which here covers the rock. The grit contiguous upon both 

 fides to the bed of whin, is confiderably harder and more corn- 

 pad than it is in any other part of the ftratification ; and that 

 angle of the grit which lies between the body of the whin and 

 its branches, is more indurated than the ftrata of the grit upon 

 each fide. 



Soil. [5Ef£5£3 



Grit in 

 vertical 

 itrata. 



Soil, 



Grit in 



vertical 

 ftrata. 



The 



riv^er. 



This fpecies of whin is not very compact in its texture. Its 

 fracture is fomewhat earthy, and is of a brownifh-black colour ; 

 but it has a considerable degree of induration, and has fome 

 fpecks of luftre in it. Having paifed this bed of whin, the grit 

 continues in the fame pofition as immediately before the whin 

 occurred ; but, foon after, the gravel, which I have mentioned 

 to be in fome places imbedded in the grit, increafes in quantity, 

 and at lad the ftrata are formed of a rock compofed entirely of 

 that fpecies of gravel, and which may be called Gravel flone or 

 Plum-pudding- rock'. This aggregate constitutes a (tratum four 

 hundred yards thick. Its ftretch is nearly from weft to eaft, 

 and it is vertical in its pofition. Its compolition confifts of 

 quartz, porphyries, and fome fmall-grained granites, all of 

 which have evidently been rounded by attrition in water : they 



are 



