Edinburgh Geological Society. 135 



chocolate reddish brown colour, arc those which were formerly 

 identified with the Old Eed Sandstone, from which, as I have shown 

 elsewhere by transverse sections and descriptions, they are separated 

 by the whole series of Lower Silurian rocks in a crystalline form. 

 The lowest members of these Lower Silurian rocks are white and 

 grey quartz rocks, regularly stratified, with intercalated bands of 

 limestone. This lower portion of the Silurian series overlaps quite 

 unconformably the Cambrian rocks on both sides of Loch Broom, 

 and their relations are all well and clearly seen near Ullapool, where 

 the overlying quartzites assume a much higher inclination than the 

 sandstones on which they rest. ... In ascending Loch Broom to its 

 western extremity on the mouth of the river Broom, nothing can be 

 clearer than the underlie of all the rocks hitherto mentioned to the 

 upper gneiss of the region in which are situated the glen of the river 

 Broom, with the mountains on either side of it. There is, however, 

 one intermediate spot above Ullapool, where the loch narrows, and 

 where the promontories on either side (one of which is called Loggie) 

 consist of diversified rocks, apparently the result of separate intrusion 

 and metamorphism. In these I met with dark diorites passing into 

 serpen tinous rocks, light, green, granular, felspathic lumps, and here 

 and there compact felspar rocks, of pinkish hue. Those convulsed 

 and broken spots, where the hard rocks have resisted denudation, and 

 consequently form the narrows of the loch, require to be more 

 thoroughly examined. This, however, is certain, that these peculiar 

 rocks are perfectly distinct from all the older rocks hitherto men- 

 tioned, and are entirely unlike any portion of the upper gneiss, with 

 which my little sketch terminates. This Upper or Lower Silurian 

 gneiss is at once distinguished from the fundamental or Laurentian 

 and non-micaceous gneiss by its flaglike character, and by its con- 

 taining such an abundance of mica as to be in parts almost a mica- 

 schist. It is, however, the grey quartzose variety of the gneiss of 

 Macculloch, and is distinctly seen to overlie all the previously- 

 described rocks, no one of which does it in any way resemble. It 

 has been usefully turned to building purposes by Mr. Fowler, who 

 has erected out of it the mansion of Braemore. It is regularly 

 bedded, and, dipping to the E.S.E. at small angles, ranges into lofty 

 mountains, which extend to Glen Fannich in the west and to Ben 

 Derrig in the south. It is occasionally traversed by small granite 

 and white quartz veins, and in such cases is often charged with 

 crystals of iron pyrites. In its extension to the S.E, the rock is tra- 

 versed also by large bosses of red granite, and then rolls over in 

 undulations from the valley of the Blackwater, until it occupies the 

 greater part of Ben Wyvis, the loftiest mountain in Eoss-shire. 

 Their order of superposition and the unconformity of these Lower 

 Silurian rocks, whether quartz rocks and limestone or the upper 

 gneiss, are perfectly clear and unmistakable ; and when we couple 

 these facts with the striking diversity of mineral character between the 

 lower or Laurentian and this upper flaggy micaceous quartzose gneiss, 

 and see that they are separated by mountain masses of Cambrian 

 sandstone, the only wonder is that it was left to me in my old days 



