366 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Doc. 1, 



Lower Silurian BocJcs (c\ c^, c^), in the form of Quartz-Bocks with 

 intercalated Crystalline Limesto7ie, foil owed hy Chloritic and Micaceous 

 JSchists, and Younger Gneiss. — These consist (in ascending order, as 

 exhibited in the general section at p. 360) of — 1. quartz-rock (c^); 

 2. limestone (c^); 3. quartz-rock (c^); (d) micaceous and chloritic 

 schists passing into a sort of gneiss, with repetitions of quartzose and 

 micaceous flaggy rocks, &c. 



Such is the succession observed in proceeding from the districts 

 of UUapool, Assynt, and Durness on the west, to the south-eastern 

 border of Sutherland, where that county is bounded by Eoss. With 

 some local deviations and rolls which reverse the inclination, the 

 prevailing dip of all these regularly stratified masses is eastwards, 

 and for the most part to the E.S.E. or S.E. Let us first consider 

 the inferior members of this group, as exhibited on the shores of 

 Loch Broom and at Ullapool in the north-western extremity of 

 Ross-shire, and as rangirig thence to the N.N.E. through the wide 

 parochial tracts of Assynt and Edderachillis, into Durness, throughout 

 which they can be more or less continuously followed for a distance 

 of not less than fifty miles, and always exhibiting the same order of 

 a central mass of limestone with underlying and overlying quartz - 

 rock strata, succeeded upwards by mica-schists and a younger 

 gneiss. 



Lower Quartz-rock. — ^The lowest beds, as seen in the west of 

 Sutherland, rest, as before said, on the Cambrian conglomerate and 

 sandstone (6), or, if that formation be absent, on the old gneiss {a). 

 Their lithological characters have recently been so well described 

 by Nicol under the name of quartzite*, that I have little to add. 

 ririe-grairied, void of mica, and usually of a light-buff or greyish 

 colour, but often weathering to a pure white, this siliceous band 

 much resembles the Stiper Stones of Shropshire, and gives the 

 clearest evidence that it is simply an altered sandstone, being not 

 only regularly bedded and jointed, but also exhibiting here and there 

 argillaceous way-boards, which have usually passed into schists. 

 This band further resembles the Stiper Stones or the typical base of 

 the Silurian rocks of Shropshire m containing Annelides (PI. XIII. 

 figs. 28-31) and Fucoids, which last also occur in the uppermost 

 layers of the lower band and immediately beneath the limestone. 



The minute cylindrical bodies which Macculloch supposed to be 

 Orthoceratites have completely satisfied Mr. Salter that they belong 

 to the class of sea- worms. I have therefore named them, in the new 

 edition of ' Siluria ' (1859, p. 222), Serpulites MaccuUochii, in honour 

 of the first discoverer of the oldest perceptible organic remains of the 

 Highland rocks. (See PI. XIII. fig. 31.) At the Bridge of Skiag, near 

 Loch Assynt, an argillaceous course occurs upon the lower quartz- 

 rock, containing casts of tortuous cylindrical bodies which are evi- 



* I prefer adhering to the old name of Quartz-rock, by which these rocks haye 

 been known from the early days of Scottish geology, and which I long ago 

 applied to the Lower Silurian Stiper Stones, showing that they were altered 

 sandstones (Sil. Syst. p. 268 et seq.). The term " quartzite " has been adopted from 

 the French. 



