NORTH SCOTLAND 



563 



entiate them. In one place this overlying, pebbly mass is 1 foot and 

 8 inches thick. The brecciated zone above referred to follows immediately 

 above this conglomerate, thus showing the whole to be a zone of prolonged 

 disturbance. The surface on which the conglomerate rests is on the 

 whole very level, though minor irregularities are noticeable. The follow- 

 ing sketch, reproduced from my notebook, shows some of these. 



This contact can be traced across the low neck (submerged at high tide) 

 which connects the island with the mainland, its position being at or just 

 below high tide, and the exposure being essentially along the strike of the 

 beds, and thus appearing horizontal. On the mainland it can be traced 

 in the cliff for some distance along the shore of the Kyle of Durness. 



The significance of this conglomerate lies in the fact that it marks a 

 period of distinct emergence, followed by erosion and resubmergence of 



Figure 1. — Disconformable Contact of Lower Ordovicic on Lower Cambric at Eilean 

 Dubh, near Durness, Scotland 



the region. The magnitude of the hiatus here represented is, however, 

 not apparent; from the physical appearances one would be tempted to 

 assign little significance to it. The fact, however, that the beds some 

 distance above carry a typical Lower Ordovicic (Beekmantown) fauna 

 makes it evident that its significance is greater than would at first appear, 

 for the entire Middle and Upper Cambric is here cut out, indicating a 

 period of prolonged exposure and of non-deposition of the later Cambric 

 strata. 



It may be added that the physical evidence of a hiatus known to exist 

 in other cases is no more marked than that found here. Such is the 

 case in the Siluro-Devonic contact in sections of western New York, 

 Canada, and Michigan, where the whole Lower Devonic is wanting, as 

 well as a part of the Upper Siluric. 



It is possible that this conglomerate marks only a minor emergence, 

 and that the great break between the Lower Cambric and the Lower 

 Ordovicic is somewhat higher. The beds which succeed the conglomerate 

 layer are at first massive, fine, calcarenites, followed by thin-bedded cal- 

 cilutites, which on weathered surfaces show a fine cross-bedding, such as 

 would be produced by migrating ripples. This is sometimes very marked, 



