the Primary Rocks and the Oolitic Series in the North of Scotland. 147 



a considerable way down Strath Peffer, they regain the most characteristic 

 form of a dark-coloured calcareo-bituminous schist, foliated, and sometimes 

 contorted, much mixed with pyritous shale, and giving- rise to sprino-s of sul- 

 phureous water. Their last appearance (at least as far as we noticed them) is 

 about two miles to the south-east of Inverness, where, in several places, they 

 form a considerable system of beds composed of grauwacke, sandstone, indu- 

 rated pyritous shale, dark, laminated limestone, &c. &c.* In this last locality 

 their relations are, however, somewhat obscure ; partly from the want of "-ood 

 natural sections, and perhaps still more from the gradually thinnino-off of the 

 older conglomerates. 



Returning to the former line of section, we enter upon the inner zone of 

 conglomerate mountains at a deep gorge, which offers a passage to the Alt- 

 Grant. The waters descend for about two miles in a narrow perpendicular 

 cleft, about two hundred feet deep, which must cut in succession through all 

 the beds in this part of the system. Its sides are, however, absolutely inac- 

 cessible : we are, therefore, obliged to seek on the banks of the Alness for 

 sections exhibiting in perfect detail tiie structure of this part of the series. 

 We there find that the chain is composed of an indefinite number of conglo- 

 merate beds, some of which are of coarse texture, and are not to be distin- 

 guished from the outer zone, which is in contact with the primary moun- 

 tains ; others (in the ascending order) are of finer texture, and pass into thin- 

 bedded, red sandstone. The coarse conglomerates gradually sink in impor- 

 tance, and, at length, become decidedly sul)ordinate to the sandstone, which in 

 some places is soft and nearly incoherent, exhibits many lines of false bedding 

 or cleavage not parallel to the planes of stratification, and is partly associated 

 with a meagre, micaceous slate-clay. In these varieties the prevailing colour 

 is red, or reddish grey, variegated with red streaks or blotches. 



Near the lower gorge (where the river escapes into the plains, which stretch 

 between the shores of the Firth of Cromarty and the base of the round-topped 

 conglomerate mountains), the more prevailing colour of the sandstone is grey, 

 or brownish grey, often ironshot, and here and there exhibiting a red tinge. 

 Some of these varieties have a coarse texture, like millstone grit, and occa- 

 sionally pass into conglomerate ; but more usually they are of a finer texture, 

 and have thick, hard (but ill-defined) beds, which are extensively quarried for 

 building. In many of these quarries, which are opened in the lower part of 

 the Alt-Grant and of the Alness, the rock cannot be distinguished from the 

 commonest varieties of gritstone which are subordinate to the English coal- 



* This system of beds is well exposed at Inche's quarry, and on the banks of a neighbouring 

 rivulet. 



