STRATA of the GRAMPIANS. 13 
the diftrict of blue:clay flate, and may almoft be faid to alternate 
with it. I have been perhaps:more minute in the defcription of 
this rock than it‘deferved; but I have been fo, becaufe doubts 
have arifen relative to what name ought to be given to this aggre- 
gate. In all my geological refearches, I have found this rock only 
twice ; once, where I have here defcribed it; and, again, near to 
Banff, on the Moray Frith. In both of thofe fituations, the ag- 
gregates are of the fame compofition, and fimilar in pofition 
they both lie among blue clay flate. 
In this long alternation, two fubftances occur which are he- 
terogeneous to the rocks among which they lie. The firft of 
thofe, is a bed of compact Felfpar, of great induration. This 
bed is ten feet broad: its ftretch is nearly from weft to eaft: its 
pofition is vertical; and it ftands between two of the layers of 
the blue clay flate. Its colour is of a reddifh-brown, with a 
fmall admixture of purple ; and its general fracture is conchoi- 
dal, fomewhat rough, but not earthy. 
Nor far diftant from this bed, an appearance occurs wor- 
thy of fome notice. Where the aggregate and the blue clay 
flate are alternating, a furface of confiderable extent of the 
aggregate rock is expofed to view, parallel to its ftratifica- 
tion. This furface is regularly undulated in {mall undula- 
tions, bearing a very fltrong refemblance to thofe that may be 
feen upon the fand of the fea-beach, when recently left by the 
tide. After paffing the bed of compact felfpar, the blue clay 
flate and aggregate rock again alternate ; but here the blue clay 
_ flate predominates. Near to this, the fecond fubftance hetero- 
geneous to thofe alternating rocks occurs. It is a bed of Whin, 
the form of which is fomewhat fingular. It confifts of a prin- 
cipal trunk, which the river, here cuts nearly at right angles. 
Upon the eaft fide of the river, this principal trunk is feen to 
fplit into three branches ; and thofe three take an eaftern direc- 
tion, between the ftrata of the aggregate rock and the blue clay 
flate, where thofe two rocks are of great induration. The 
breadth: 
