STRATA of the GRAMPIANS. i 3 



the diflrict 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 irdeferved ; 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 composition, and fimilar in pofition l 

 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. 



Not 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 considerable extent of the 

 aggregate rock is expofed to view, parallel to its ftratifica- 

 tion. This furface is regularly undulated in fmall undula- 

 tions, bearing a very ftrong refemblance to thofe that may be 

 feen upon the fand of the fea-beach, when recently left; by the 

 tide. After pafling 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 lingular. 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, betw r een the ftrata of the aggregate rock and the blue clay 

 flate, where thofe two rocks are of great induration. The 



breadth. 



