3S6 Dr. Mac Culloch on the Parallel Roads of Glen Roy. 



In terminating this description I may remark, that the topo- 

 graphical deficiencies which may be found in it are irremediable 

 until an accurate geographical survey of this country shall be made, 

 but that these deficiencies can not materially affect the arguments 

 about to follow, whatever additions they may chance to make to 

 them. 



In as far as the mineralogical structure of the country is con- 

 cerned in the description of the lines of Glen Roy, I have already 

 noticed the principal facts in describing the nature of the alluvia 

 which form the surfaces of the hills. I may however proceed to 

 say, that the natural rock is not often visible on their faces, although 

 k may be observed in most parts of the bed of the river. I have 

 already briefly remarked that at the upper part of the valley 

 it consists of a hard micaceous schist traversed by veins of red 

 granite. The same rock is continued upwards towards the source 

 of the Spey till the granite itself appears ; which forms the most 

 elevated part, and that only, of the country between the sources of 

 the Spey and of the Roy. But in proceeding from the head of 

 Glen Roy to its mouth, the granite veins gradually disappear ; 

 various sorts of schist, micaceous, quartzose, and argillaceous, oc- 

 curring in an irregular order and at various elevations. The beds 

 are sometimes to be seen absolutely horizontal, and at others as 

 completely vertical ; and I need hardly say that they occupy all the 

 intermediate angles. A similar construction extends through Glen 

 Gloy, and along the sides of Loch Lochy, as well as the skirts of 

 Ben Nevis. 



The different opinions which have been entertained relative to 

 the origin of these lines, or Roads, as they have most commonly 

 been supposed, render it necessary to describe their form and ma- 

 terials ; which the accompanying sections, with the aid of a few 



