1852.] SHARPE ON THE HIGHLANDS. 127 



extent of micaceous scMst. Thus there has been a sort of conspiracy 

 to give an undue importance to the Clay-Slate, which has got mapped 

 of nearly double its real width ; and which, as far as I could learn, 

 contains no subordinate beds of limestone. 



In the eastern part of its course, the band of clay-slate belongs to 

 a single formation, being a dark grey or dark blue slate, of nearly 

 uniform character, the finer beds of which are worked in many places 

 for roofing slate : but to the westward there are two formations of 

 slate, whose mineral characters are sufficiently different to make it 

 desirable to distinguish them. The lower of these two is the dark 

 bluish grey slate just mentioned, over which lies a series of beds of 

 great thickness of a light green or greenish grey chloritic slate, con- 

 taining beds of slaty conglomerates of a similar green colour, full of 

 small pebbles of white quartz, which are here and there so abundant 

 as almost to deprive the rock of its slaty character. With these few 

 exceptions, both the bedding and the cleavage of the slates of both 

 series are well marked throughout their course. 



We cannot decide the age of these slates until organic remains have 

 been found in them ; but, in the absence of such conclusive proof, we 

 must fall back on the best evidence we can obtain, which is that of 

 mineral character : this leads me to compare them to the two great 

 Slate Formations of Westmoreland and Cumberland, long since di- 

 stinguished by Professor Sedgwick, viz. the green slate, chloritic, 

 quartzose, and often brecciated, overlying the dark clay-slate of 

 Skiddaw. 



The position of these slates differs so much in various parts of 

 their course, as to make it necessary to describe in detail the sections 

 visited; in doing which I will commence at the east where their 

 arrangement is least complicated. 



Fig. 1. — Section from the Brig-o-Callyy in Glen Shea, to Blair 



Gowrie. 



N.W. S.E. 



Brig-o-Cally. Craig Hall. Blair Gowrie. 



Mica-schist. Clay-slate. Trap. Old Red Sandstone. 



Figure 1 is a section from the Brig-o-Cally in Glen Shea to Blair 

 Gowrie. The clay-slate dips at an angle of about 30° towards the 

 mica-schist, being obviously thrown into that position by a great dyke 

 of greenstone trap which separates it from the Old Red Sandstone. 

 The actual boundary between the schist and slate was not seen : the 

 band of slate is about three miles wide. It has been quarried for 

 roofing slate about one mile below the Brig-o-Cally. The Old Red 

 Sandstone, in the picturesque gorge below Craig Hall, is a coarse 

 breccia containing large boulders of quartz, jasper, &c., in a matrix 

 which has been altered by the influence of the neighbouring trap into 

 a crystalline mass. Half a mile lower down the river, the conglo- 

 merate is found unaltered, and thus it continues to Blair Gowrie. 



