8 DESCRIPTION of the 
tinue their direction upwards, decreafing in their diameters as 
they afcend, until they finifh 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 com- 
pact 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. 
Vari Soil. 
Grit in Grit in 
Aan ! vertical 
rata. 
ftrata. 
The 
river. 
Tus {pecies 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 confiderable degree of induration, and has fome 
f{pecks of luftre in it. Having paffed 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 laft the ftrata are formed of a rock compofed entirely of 
that fpecies of gravel, and which may be called Gravel-{tone or 
Plum-pudding-rock. This aggregate conftitutes a ftratum four 
hundred yards thick. Its ftretch is nearly from weft to eaft, 
and it is vertical-in its pofition. Its compofition confilts of 
quartz, porphyries, and fome fmall-grained granites, all of 
which have evidently been rounded by attrition in water: they 
are 
