I'rof. C. La])icortJi — Close of the Highland Controversy. 103 



of a new and a happier period like that of the earlier years of the 

 present century, when all British geologists shall meet upon an equal 

 footing, in mutual communion and sympathy, and when the only 

 rivalry between parties shall be in vieing with each other in develop- 

 ing the unknown treasures in that new geological world of wonder 

 now opening up before our eyes, where authority and precedent are 

 alike unknown, and where so much awaits discovery that there is 

 room and work and hope for all. 



Appendix. 



On the Stratigraphy and Metamorphism of the Eocks op the 



Durness Eriboll District.^ 



By Charles Lapworth, LL.D. , F.G.S., 



Professor of Geology and Mineralogy, Mason Science College, Birmingham. 



In * the district round Eriboll and Durness, the so-called Eastern 

 (or Upper) Gneiss is composed of two very distinct members. The 

 older member is the Arnaboll Gneiss, which is, in my opinion, 

 nothing more nor less than the so-called Laurentiau (or Lower Gneiss) 

 brought up to the east of the Assyut (Durness-Eriboll) series by 

 gigantic overfolds. 



The younger member, which is composed of tlie schistose meta- 

 morphic rocks of the Moen and Central Sutherland, contains within 

 it — forming almost inseparable parts of its mass — long strips and 

 patches of the lower zones of the Assynt (Durness-Eriboll) series. 

 The schistose quartzites or the quartz-schists (of some authors) of the 

 Sutherland Schist Series are actually nothing more than the crushed 

 and mechanically metamorphosed ends of long wedges of the Assynt 

 Series, and are often in visible continuity upon the ground with the 

 unaltered Assynt beds. 



I hold that the Sutherland Schistose Series is composed of a com- 

 plete intermixture of Ai'chtean and Assynt rocks, the two series 

 being so interfolded and interfelted together that (exception being 

 made of those zones near the great overfaults where the metamor- 

 phism is incomplete) they can never be separated in the field, but 

 must be mapped simply as " metamorphic." 



The planes of foliation and schistosity in the (so-called) Upper 

 Metamorphic Series of Sutherland are not planes of bedding ; they 

 are planes of cleavage — that is, gliding-planes, along which the 

 rocks have yielded to the irresistible pressure of the lateral Earth- 

 creep during the process of mountain-making. This pressure was 

 so extraordinary that granites, syenites, pegmatites, gneisses, and 

 quartzites have been crushed to powder, and have been finally flat- 

 tened out into rocks having all the external characters of hiilleflintas 

 and even finely laminated shales. Every stage of the crushing pro- 

 cess is recognizable in the field and under the microscope, from the 

 coarsest pegmatite and gneiss down to the so-called metamorphic 

 shales, schists, and slates. Hence the most highly metamorphosed 



^ Bead at Ordinary Meeting of Geologists' Association, July 4th, ISSi. 



^ The communication is printed as read. A few words have heen added by Prof. 

 Lapworth for the sake of clearness of description. These are given in brackets. — 

 J. J. H. Teall. 



