IN THE NOETH-WEST HIGHLANDS OF SCOTLAND. 425 



limestones with the Caledonian series, thus regarding thcra as of 

 Pre-Cambrian age. But in the course of the survey of that region 

 we found that the false-bedded quartzites, the " pipe-rock," the 

 " Fucoid-beds," the Serpulite-grit (with the Serpulites) are associated 

 with the crystalline limestones and the intrusive sheets, the whole 

 series being intersected by numerous thrusts which develop new 

 structures of an important kind. 



Advancing southwards to the confines of Assynt, we find evidence 

 of an extraordinary overlap of the Moine Thrust-plane, along 

 the base of the Cromalt Hills to the south of Elphin and Loch 

 Urigill. From the base of the Stack of Glencoul the outcrop of 

 this thrust-plane can be traced continuously, southwards by Loch 

 Ailsh, thence crossing the Oykel and AUt Ealag in a S.S.W. 

 direction. From the latter point it runs luest for a distance of six 

 miles, along the base of the north slope of the Cromalt Hills to the 

 famous Knockan cliff south of Elphin, p>assing transgressively across 

 the Ben-More Thrust-plane and all underlying thrusts, till the mica- 

 ceous flagstones rest at various localities on the undisturbed Silurian 

 strata. 



Between Loch More and Glencoul the belt of complicated ground 

 extending from the outcrop of the Moine Thrust westward to the 

 edge of the undisturbed Silurian strata varies from two to four 

 miles ; while from Glencoul to the base of the Cromalt Hills, the belt 

 averages about six miles in width. When we reach the Knockan 

 cliff, the southern prolongation of this complicated ground is buried 

 underneath the materials borne along the plane of the Moine Thrust. 

 Indeed, had it not been for the extensive denudation of the strata 

 above the latter thrust-plane, we should never have been able to 

 study the sequence of these terrestrial movements, or the various 

 stages in the production of the Moine schists. 



With the view of showing the belt of complicated ground, com- 

 prising displaced Archaean, Cambrian, and Silurian strata, along the 

 northern margin of this great overlap, the accompanying horizontal 

 section (fig. 19) has been drawn from Elphin eastwards by Am Pollan 

 and Cnoc na Glas Choille, to the outcrop of the Moine Thrust-plane 

 in AUt Ealag. 



At Elphin, close to the road leading to Ullapool, the " Fucoid- 

 beds " and Serpulite-grit are truncated by a powerful major thrust, 

 bringing forward the piled-up " Fucoid-beds," Serpulite-grit, and 

 basal limestone. The latter are abruptly cut off by another major 

 thrust-plane, along which the Eilean Dubh limestones have been 

 driven, repeated by innumerable minor thrusts, for a distance of 

 two miles. At Am Pollan, these displaced limestones are capped by 

 an outlier of the materials lying above the Ben-More Thrust-plane, 

 consisting of Archaean rocks covered unconformably by the Cam- 

 brian sandstones and the basal quartzites, the latter resting uncon- 

 formably on both. Advancing eastwards, the strata are mainly 

 composed of piled-up limestones, which, at the base of the west 

 slope of Cnoc na Glas Choille, are overlapped by the Silurian strata 

 lying above the main outcrop of the Ben-More Thrust-plane. In the 



