478 Geological Society. 



The author particularly cited the observations of Professors Ram- 

 say and Harkness, in illustration of tliis essential feature of the 

 passage upwards from this quartzose and calcareous series into the 

 " Eastern or Upper Gneiss ", as seen on the hanks of the River Oykel 

 in Ross-shire, and thence ranging to Kinloch-Ailsh in Sutherland, 



To show how in the limited space of a few miles there was an en- 

 tire discrepancy between the Fundamental Gneiss and the strata 

 overlying the quartz-rocks and limestones, two transverse sections 

 were exhibited, the one along the banks of Loch Stack and Loch 

 More, the other across Loch Eriboll to Ben Hope. Both of these 

 exhibit a conformable overlying succession from the quartzose and 

 calcareous strata into overlying micaceous fiag stones, which though 

 occasionally so metamorphosed as to resemble a sort of gneiss, are for 

 the most part very unlike that rock, and when viewed en masse 

 can everywhere be distinguished from the Lower Gneiss ; to say no- 

 thing of their greatly overlying position and their having a strike 

 and dip entirely discordant to that ancient rock. 



Attention was peculiarly directed to the details of the section 

 across Loch Eriboll, where a large Orthoceratite had been discovered 

 by Mr. Clark, in a strong band of quartz-rock between the Lower 

 and Upper Limestone, and where, in the escarpment above the house 

 of that gentleman, the clearest proofs are seen of an unbroken and 

 conformable succession from the quartzo-calcareous members of the 

 series up into the quartzo-micaceous and chioritic rocks (" Upper 

 Gneiss") which range across Loch Hope and rise to the summit of 

 Ben Hope, 3040 feet above the sea. 



In its advance on the dip to the east, this overlying micaceous 

 and flag-like series occasionally becomes gneissose, particularly in 

 those tracts south and east of Tongue, and along the eastern frontier 

 of Sutherland, where intrusive granitic, syenitic, and felspathic rocks 

 prevail infinitely more than in the western tracts. 



Particular attention was given by the author and Prof. Ramsay, 

 and subsequently by Prof. Harkness, to the existence of a zone of 

 intrusive rocks, which seemed to Prof. Nicol to produce a decided 

 separation between the Silurian Rocks with fossils and the " Eastern 

 Gneiss." In the escarpment above Eriboll House, the only igneous 

 rock observable is a very thin course of a few feet of felstone, which 

 is quite conformable to the strata, and produces no sort of disruption 

 among them. In proceeding northwards, or towards Whiten Head, 

 these igneous rocks, chiefly of red compact felspar and white quartz, 

 protrude in startling and irregular masses, particularly in Ben Ar- 

 noboU ; but neither there nor at the Whiten Head upon the Northern 

 Ocean (which the author visited thirty-three years ago in company 

 with Prof. Sedgwick) do these felspathic rocks produce any real 

 severance between the quartzose strata and the so-called " Eastern 

 Gneiss," which latter, in the form of deep-green micaceous and 

 hornblendic schists, overlies the quartz- rock conformably, both sets 

 of strata dipping together to the E.S.E. A similar ascending suc- 

 cession of the strata was shown to exist in Assynt and on Loch More, 

 notwithstanding the occasional interpolation of igneous rocks. 



It was announced that the small map, the publication of which 



