172 Peter Macnair — Altered Clastic Rocks 



to pass downwards into them, though they are soon covered by the 

 later Old Eed Sandstone conglomerates. Above the argillaceous 

 zone, however, a strong and constant band of these arenaceous rocks 

 is well developed. Along the shores of Loch Lomond they are to be 

 seen below Rowardennan, being also well exposed near Sallachie 

 Wood, from whence they strike northwards, being well developed 

 along the northern shores of Loch Katrine. Still further eastwards, 

 massive beds characteristic of this zone are seen in Ben Ledi ; 

 passing further along the line of strike, they are shown in Ben 

 Vorlich, around St. Fillans, in Glen Leadnock, thence by Dunkeld 

 Bridge of Cally, and onwards to the sea above Stonehaven. The 

 rocks of this lower arenaceous group are easily recognized by their 

 scarcely altered fragmental aspect, showing little or no evidence of 

 the intense metamorphism which is to be found nearer the centre of 

 the Highland area. They have, of course, been more or less indu- 

 rated, but they rarely show such evidences of extreme crystallization 

 and foliation as are to be found amongst some of the higher zones to 

 be described. The rocks of this zone vary from exceedingly fine 

 light or dark greywackes (which are hardly to be recognized from 

 an igneous rock, so fine is their texture through grits, with their 

 pebbles of quartz and felspar set in a fine matrix of comminuted 

 felspathic matter) to massive conglomerates with pebbles, often as 

 large as an inch and more in diameter. These fine-grained grey- 

 wackes often exhibit a closely banded structure of lighter and darker 

 shades of grey, which is undoubtedly referable to the original 

 sediments out of which the beds have been formed. 



V. Middle Arenaceous Zone. 



The next zone in ascending oi'der is that to which we have given 

 the name middle arenaceous zone, because it is found to lie between 

 the lower arenaceous group just described and an upper argillaceous 

 and arenaceous zone, from both of which it is easily distinguished by 

 its lithological features. Intercalated in this group occurs the Loch 

 Tay limestone zone, about to be described. 



The characteristic rocks of this middle arenaceous group are 

 a series of mica-schists, quartz-schists, and grits. They are more 

 highly foliated than the arenaceous groups below, and seem to have 

 suffered a further degree of metamorphism. Upon the whole, they 

 seem to present moi'e of an arenaceous than an argillaceous affinity, 

 they being easily distinguished, as I have already remarked, from 

 the arenaceous band below. Geographically, they extend in a broad 

 band across the country in a similar manner to those zones just 

 described, occupying the region between the lower arenaceous group 

 on the south and the upper argillaceous zone on the north. They 

 are well exposed in the valley of the Dochert, the braes of 

 Balquhidder, also on the hills that lie between Loch Earn and Loch 

 Tay, stretching north-eastwards by Aberfeldy, Pitlochry, and thence 

 onwards into the Eastern Grampians, where they seem to have been 

 largely displaced by the later eruptive masses of granite and other 

 igneous rocks. 



