516 Geologica I Society : — 



observers, in so far as they forestalled the conclusions to which the 

 Geological Survey had been led. Reference was made to the obser- 

 vations of Macculloch, Hay Cunningham, C. W. Peach, and Salter ; 

 to the prolonged controversy between Sir Roderick Murchison and 

 Professor Nicol ; to the contributions of Hicks, Bonney, Hudleston, 

 Callaway, Lapworth, Teall, and others. It was shown that Nicol 

 was undoubtedly right in maintaining that there was no conformable 

 sequence from the fossiliferous quartzites and limestones into tbe 

 eastern scbists. It was also pointed out that the conclusions of 

 Professor Lapworth regarding the nature and origin of the eastern 

 schists involve an important departure from Nicol's position, and 

 are practically identical with those obtained independently by the 

 Geological Survey. 



The results of the recent survey work among tbe Archaean rocks 

 may be thus summarized : — (1 ) the eruption of a series of igneous 

 rocks of a basic type in which pegmatites were formed ; (2) the 

 development of rude foliation in these masses, probably by mechanical 

 movement, and their arrangement in gentle anticlines and synclines, 

 the axes of which generally run N.E. and S.W. ; (3) the injection 

 of igneous materials, mainly in the form of dykes, into the original 

 gneisses, composed of (a) basalt rocks, (b) peridotites and palaeopicrites, 

 (c) microcline-mica rocks, (d) granites ; (4) the occurrence of mecha- 

 nical movements giving rise to disruption-lines trending N.W. and 

 S.E.,E. and W., N.E. and S.W. ; (5) the effects of these movements 

 on the dykes were to change the basalt-rocks into diorites and 

 hornblende-schists, the peridotites and pakeopicrites into talcose 

 schists, the microcline-mica rocks into mica-schists, and the granites 

 into granitoid gneiss ; (6) the effects on the gneiss resulted in the 

 formation of sharp folds trending generally N.W. and S.E., the 

 partial or complete reconstruction of the original gneiss along the 

 old foliation-planes, and finally the development of newer schistosity 

 more or less parallel with the prominent disruption-lines. 



There is an overwhelming amount of evidence to prove that all 

 these various changes had been superinduced in the Archaean rocks 

 in Pre-Cambrian time. 



After reviewing the facts bearing on the denudation of the Ar- 

 chaean land-surface, the order of succession and thickness of the 

 Cambrian strata were given, from which it is apparent that tbe 

 deposits gradually increase in thickness as we pass southwards from 

 Durness to Loch Broom. 



Prior to the deposition of the Silurian sediments the Cambrian 

 strata were folded and extensively denuded. By these means 

 various Cambrian outliers were formed far to the east of the present 

 limits of the formation. 



The order of succession of the Silurian strata along the line of 

 complicated structure from Eriboll to Lllapool Avas described, ref< r- 

 ence being made to the further subdivision of the " Pipe-rock " and 

 the Ghrudaidh Limestones (Group I. of Durness section). None of 

 the richly fossiliferous zones of Durness is met with along this line, 

 as they occupy higher horizons. An examination of the fossils 



