104 Prof. C. Lapicorth — Clone of the Highland Controversy. 



rocks of Eriboll are not the coarse Hebridean Gneisses, but the fine 

 slaty schists. 



The process of rock-folding in the region is exceedingly complex, 

 and has resulted in most remarkable phenomena. The rock-folds 

 (and faults) are of all grades, from miles across down to microscopic. 

 In some cases the original dividing plane (either bedding plane or 

 fault plane) of two successive rock-sheets has been twisted into the 

 form of spirals, cornucopias, etc. Folding, interfolding, buckling, 

 shearing, stretching have all taken effect again and again along the 

 junction (fault or bedding) plane between the Sedimentaries and 

 Archasan ; and innumerable protrusions of igneous rock — plutonic — 

 have foi'ced their way in numberless veins in the latter (Archaean) 

 up to the former (Sedimentaries). At present, even near the line 

 where the two distinct sets of rocks retain their recognizable 

 individuality, the schistose layers that form the so-called lowest 

 beds of the Eastern Schists are (occasionally) compounded of 

 materials of such different origin that even in the same hand- 

 specimen (from one locality) I believe that it can be sometimes 

 demonstrated that certain parts of a layer may be mainly Assynt, 

 other parts mainly Archtean, and other parts mainly intrusive or 

 segregatory. The result is a comparatively homogeneous schist ; 

 but who shall indicate its geological age ? 



Schists composed of Archsean, Ordovician (sedimentary), and 

 intrusive rocks respectively, form part and parcel of one and the 

 same (lowest or heterogeneous) zone in the Eastern (Schistose) area, 

 and intermingled with them occur schists (apparently) composed 

 of mixtures of all three in different degrees. Here and there near 

 the junction line (between the present Durness-Eriboll Series and 

 the present Eastern Metamorphic Series) we can say : This band 

 (a) is essentially or wholly Archsean ; this (b) is certainly Ordovician ; 

 and this (c) probabl}'^ intrusive rock. But as we go further east all 

 recognizable distinctions vanish one by one, and in the present 

 state of our knowledge all that we can presume to say is, that, 

 considered as a whole, the Eastern Schist of Central Sutherland is 

 in all probability an intimate compound of sheets of (1) Archa9an, 

 (2) Sedimentary, and (3) Intrusive rocks, which have been crushed into 

 slaty rock, in which crystallization has set up along the cleavage planes. 



The quartz, and possibly some of the mica, of the Upper Schists 

 may have been largely derived from the Sedimentaries ; hence the 

 highly quartzose nature of these schists. Their felspar has either 

 been derived from the Archasan, or from intrusive plutonic rocks. 



So far as my own observations go, there seems to be no trace what- 

 ever of any sedimentary rock in the Durness-Eriboll region of more 

 recent date than the Durness Limestone. The thin, so-called Upper 

 Quartzite band of Sango Bay is the crushed basement zone of the 

 Lower Quartzite. The green schists overlying it are pressure schists, 

 formed and brought over in the great overfault. The same zone 

 occurs again in Eriboll, along the great fault-line of the LTpper Schist 

 series. If (like those geologists who erroneously maintain that these 

 Sango Bay Schists, etc., naturally succeed the Durness Limestone), 



