16 DESCRIPTION of the 
from weft to eaft, and a foutherly dip. To endeavour to have 
thefe appearances more fully explained to me, I directed my 
fteps to the brow of that hill, where I had obferved the rock laid 
bare; and in pafling along the fronts of the hills from eaft to 
weit, I foon came to a dike of porphyry fimilar to thofe which I 
had immediately left. This dike is fixty feet broad, ftretching 
nearly from fouth to north, and flanked upon both fides by mi- 
caceous fhiftus, ftretching and dipping as before defcribed. In 
proceeding farther along the faces of thofe hills, I found feveral 
other dikes of porphyry, of various breadths, and at various di- 
{tances from each other ; but all of them fimilar in their lines of 
direGtion, and the micaceous fhiftus always interpofing between 
them, through which they feemed to rife. The porphyries of 
thofe dikes are generally of a ferruginous colour, tending fome- 
times to an orange-red, and of various tints of thofe colours. 
They have great induration, are coarfe-grained, and produce a 
rough fracture. The particles of quartz which are fcattered in 
their principal mafles, are fmall, amorphous, and are of a ferru- 
ginous colour. The particles of felfpar are of a light tint of the 
fame colour, and are moftly cryftallized. The furface of thofe 
dikes are in many places bare, and expofed to the eye for long 
extents, in their lines of direCtion; and in all thofe lines of di- 
yeCtion which I have traced, I have never found any of them al- 
ter in their breadths, in their verticality, nor in their direions. 
Their furfaces, in general, confift of oblong fquare blocks, now 
loofe and unconnected with each other; and, in many places, 
the lines of fraéture of thofe blocks are fo ftraight, that one 
might almoft fuppofe that they-had been disjoined by the hand 
of art. 
I nave often obferved, in this diftria, and in other parts of 
the Grampians, that the loofe and outlying blocks of both gra- 
nite and of porphyry, (which have not been worn down by at- 
M trition), 
