428 



RECENT WOEK OF THE GEOLOGICAL STTEVEY 



the east at an angle of 35° ; but in places it lias been folded, and the 

 materials lying above it have been denuded away. Hence we 

 find, to the west of Glastullich, that it is overlapped by the Moine 

 flagstones, which there rest directly on the thrust Silurian lime- 

 stones. 



Prom the Achall valley southwards to Ullapool the outcrop of 

 the Ben-More Thrust-plane can be traced almost continuously by 

 means of the Archaean rocks. In two places, however, it is over- 

 lapped by the Moine Thrust, which ushers in the micaceous flagstones. 



To the east of Ullapool there is an undisturbed order of succession 

 from the basal quartzites to the Serpulite-grit. Along this latter 

 horizon there is a povrerful major thrust, bringing in a portion of 

 the Cambrian sandstones overlain unconformably by the basal 

 quartzites and succeeded by the various members of the Silurian 

 series up to the limestone. Polio wing the line of outcrop of this 

 major thrust, southwards by the Braes of Ullapool to the shore of 

 Loch Broom, a large mass of Cambrian sandstone appears above the 

 plane, resting on the Serpulite-grit and spreading over a considerable 

 area to the north of Corry Point. Near the latter locality the 

 basal quartzites, in several places, rest unconformably on the Cam- 

 brian sandstones (fig. 22). 



Pig. 22. — Horizontal Section south of Ullajpool. 

 (About 1 mile in length.) 



Passing eastwards, the Cambrian and Silurian strata borne along 

 by this major thrust are abruptly truncated by the Ben-More 

 Thrust-plane, well exposed at various localities. Along the western 

 face of the disrapted gneiss, small patches of Cambrian strata rest 

 unconformably on the latter with an inverted dip towards the plane 

 of disruption. Eventually within a short distance the Archaean 

 gneiss is overlapped by the micaceous flagstones above the Moine 

 Thrust-plane. 



To the south of Loch Broom the major thrust, which forms 

 such an important feature in the geological structure of the Ullapool 

 and Achall districts, is entirely overlapped by the Ben-More Thrust- 

 plane, bringmg forward a large slice of the old Archaean platform, 

 consisting of gneiss with numerous basic dykes, covered unconform- 

 ably by patches of Cambrian conglomerate and sandstone. 

 Advancing southwards towards Little Loch Broom, the materials 

 lying above the Ben More Thrust-plane consist almost wholly of 

 Cambrian strata, w^hich, at Dundonald, have been converted into 

 schists. Indeed, so striking is the metamorphism developed by 



