1859.] MimcnisoN — xorth highlands. 233 



masses, as laid down in the accompanying map of Sutherland*, 

 whilst some of them extend into Ross-shire. Again, Prof. Ramsay 

 found such felspathic rocks in a similar position northwards near 

 the head of Loch Coul. 



However devious their outlines, and however much they are occa- 

 sionally developed, these intrusive felstones never break up the order 

 of succession, even where they are interwoven with the metamorphic 

 Lower Silurian strata. Thus, if the observer, instead of selecting 

 such transverse sections as those on which I have naturally insisted, 

 as being the most free from such eruptive agency, chooses to pass 

 over any of these igneous hilly masses in proceeding from west to 

 east, he will still find the strata on both their flanks dipping to the 

 east, — that is, to the S. or N. of east, according to the sinuosities and 

 projections of the more ancient rocks upon which these Lower Silu- 

 rian deposits were originally accumulated. 



In short, the granitic felstones and syenites so largely developed 

 in the eastern parts of Assynt, and which rarely if ever occur be- 

 tween the limestones and the upper quartz, but chiefly either in the 

 latter or in the younger or overlying flagstones, no more hinder the 

 observer from developing a clear and conformable order of super- 

 position, than the true porphyries and other intrusive rocks have 

 prevented the Geological Surveyors from working out the regular 

 order of the associated Lower Silurian types of Wales f. 



A most instructive lesson, in regard to the operation and effect of 

 the intrusion of the red felstones, is to be seen at the Whiten Head, 

 or maritime eastern headland of the noble bay of Loch Eriboll. 



There, the quartz-rock series of the loch appears with its usual white 

 aspect, when blanched by atmospheric action, — the cliff's with nume- 

 rous caverns facing the bay being composed of that rock, without 

 any associated limestone, which, as before said, thins out in its course 

 from S.S.W. to N.N.E. On rounding the headland in a boat (a very 

 calm day favoured usj), the grandest scene, both for the painter and 

 the geologist, was exposed to our sight. Numerous jagged rocks of 

 quartz stand out — some pertaining to the mainland, others forming 

 detached stacks in the sea,— one of which lias a height of about 150 

 feet. Threading through these pinnacles and proceeding to the east, 

 we found the whole of these white quartzose strata dipping east- 

 wards or to the E.S. E., and then uverlaiii hy a great mass of dark chlo- 

 litie and micaceous s' hist, whieh is penetrated in devious directions 



by eruptive bosses ami veins of a light-red igneous rock, composed 

 chiefly of felspar with Bome light-coloured quarts, certain veins of 

 which cut across the strata, whilst others run parallel to them. 



Although this eruptive rock has doubtless passed up through the 

 -tratitied quarts-rook (one of the detached Btaoks exposing, indeed, 



* This map was exhibited al the Meeting of the Society. The chief features 

 nre givrn in the reduced sketch-map, PL XII. in Vol. w.. published in No. 62. 



t Sec the sheets of the Geological Store] M:i|> of North Wales, and the illus- 

 trative sections. 



| I | >: i — . -< 1 under these cliffs in a boat with Prof, Sedgwick in 1827 I hut the 

 mi then t"" high t<> allow .if our examining the rocks 



