168 Peter Macnair — Altered Clastic Rocks 



II. Wokk of Previous Observebs. 



Before passing to the more immediate subject of the paper, 

 I would here briefly refer to the work of some of the previous 

 observers upon this district, and that for a more particular reason, 

 namely, that justice may be done to one of the most illustrious 

 names connected with Scottish geology, I mean James Nicol, whose 

 knowledge of the Highland rocks and abilities as a stratigrapher 

 was far in advance of his time. 



In the years 1860-1 Murchison and Geikie, 1 and also K. Harkness, 2 

 published papers dealing with certain traverses of the Southern and 

 Central Highlands. These papers were naturally based on the 

 supposed succession in the north-west of Sutherlandshire, so that 

 iheir observations were no doubt to a great extent overshadowed by it, 

 Murchison and Geikie being of course predisposed to the old theory, 

 so that they saw nothing in these traverses but what conformed to it, 

 and that, simply put, was that all the rocks below any limestone 

 band were quartzose and flaggy, and represented their lower series, 

 and all above it were micaceous and schistose, and representing 

 I heir upper series ; though the latter seems to have had serious 

 doubts on the matter, not being able to make nature fit the theory, 

 the consequences of the whole being that the true mineralogical 

 character of the beds and their stratigraphical succession escaped 

 them. 



The paper of Harkness bears upon itself such evident mis- 

 conception of the mineral characters of the Highland rocks, which 

 had already been established by such observers as Maculloch, as 

 to render it entirely worthless from a geological point of view. 

 For instance, a comparison of the description of the Pass of Leny 

 section with that given by Nicol the following year, shows clearly 

 the difference in value of the two observers' work. 



Turning now to Nicol's paper, 3 published in 1862, we find it 

 thoroughly characteristic of the man. His reading of the sections 

 are simple descriptions of what he saw in nature. At the outset 

 he states the object of his paper, which was to investigate the 

 relationships of the three great formations, the clay-slate, the mica- 

 slate, and the gneiss ; and though he seemed to be burdened with the 

 Wernerian doctrine of their succession, yet his paper seems to me to 

 show his masterly conception of what the unravelling of the Highland 

 rocks meant. The manner in which he chose his sections, and the 

 faithful description he gave of their rocks, are scarcely surpassed 

 by those of the Geological Survey of the present day, who have 

 adopted much the same methods in attacking the Highland problem. 

 His method was to take a series of sections at different points from 

 east to west across the Highlands from the verge where they abut 

 against the Old Eed Sandstone, explaining their principal mineral 



1 "Altered Rocks of the Central Highlands" : Quart. Journ. Geol. Soc. 1861. 



2 " On the Rocks of Portions of the Highlands of Scotland" : Quart. Journ. Geol. 

 Soc. 1861. 



3 " Southern Grampians" : Quart. Journ. Geol. Soc, vol. xix, p. 180. 



