414 EECENT WOEK OF THE GEOLOGICAL ST7EVET 



this tendency, the Cambrian and Silurian strata resting on the 

 Archaean rocks brought forward by one of these powerful thrusts, 

 fold over the western face of the displaced gneiss and actually un- 

 derlie the Archaean rocks in inverted order. 



e. Erom the foregoing phenomenon (cZ) it follows that along the 

 line of outcrop of a maximum thrust the materials above the plane, 

 in contact with the underlying strata, may consist of either 

 Archaean rocks, Cambrian sandstones, or some zone of the 

 Silurian series. Por example, along the outcrop of the Glencoul 

 Thrust, in Loch Glencoul and Loch Glendhu, the Archaean gneiss 

 rests directly on the piled-up Silurian strata ; but when it is traced 

 southwards towards Inchnadamff, the thrust brings the quartzites 

 to overlie the limestones along the base of the western slope of 

 Glasven. In like manner, along the outcrop of the Ben-More Thrust, 

 at one point the Archaean gneiss is made to overlie the piled-up 

 Silurian strata, at another point the Cambrian sandstones are brought 

 in contact with the heaped-up beds, while at a third point different 

 members of the Silurian series are thrown against each other. 



All these various features are beautifully illustrated along the line 

 of complicated structure between EriboU and Ullapool. 



5. Horizontal Sections illustrating the Physical Relations 

 of the Strata between EriboU and Ullapool. 



In order to show the remarkable variations in the geological 

 relations of the strata and the extraordinary complexity of the 

 structure, we propose to describe a series of horizontal sections 

 drawn across the general strike of the sedimentary deposits and the 

 eastern schists, leaving out minute details. 



Section from Ben ArJcle to the Moine Thrust-plane (fig. 9). — Be- 

 ginning with the tract lying to the north of Loch More, there is a 

 magnificent example of the abnormal thickness of the quartzites, due 

 to the piling-up of the beds by minor thrusts or|reversed faults. Indeed 

 there is no finer instance along the line to Ullapool. So deceptive is 

 the structure that, were it not for the subdivisions of the " pipe-rock " 

 recently established, the task of unravelling the complications would be 

 hopeless. Along the western base of the mountain, the basal quartzites 

 rest unconformably on the old Archaean platform : but a short distance 

 up the slope a great major thrust-plane occurs, separating the under- 

 lying undisturbed quartzites from the overlying displaced beds. Along 

 the " sole " of this major thrust the zones of the quartzite, chiefly of 

 the " pipe-rock," have been driven, piled on each other by minor 

 thrusts or reversed faults, the latter being truncated by the former. 

 In tracing these reversed faults, the band of Serpulite-quartzite in 

 the " pipe-rock " has been of the utmost service. Advancing east- 

 wards to Loch-an-na-Paoilege, the same phenomenon is met with, 

 viz. the constant repetition of various zones of the quartzites by minor 

 thrusts. Eventually the " pipe-rock," " Eucoid-beds," and Serpulite- 

 grit are repeated by similar displacements, till they are overlapped 

 by a maximum thrust, bringing forward a slice of Archaean rocks 

 with the basal quartzites. By means of another maximum thrust 

 a belt of green schist and sheared gneiss, with recognizable bands of 



