TO THE NORTH-WEST HIGHLANDS OF SCOTLAND. 



403 



Fig. 6. — Diagram showing the Formation of Outliers of Cambrian 

 Strata by folding and denudation in Post-Cambrian and 

 Pre-Silurian time. 



1. Archaean. 1'. Pre-Cambrian Plane of Marine Denudation. 



2. Cambrian. 2'. Pre-Silurian Plane of Marine Denudation. 

 3-7. Silurian. 



III. The Silurian Formation. 



1. Uniformity in the Order of Successsion. 



The results of our researches along the line of complicated struc- 

 ture from Eriboll to Ullapool demonstrate the remarkable uniformity 

 of the order of succession of the Silurian formation. All the various 

 zones and even the minor subdivisions, from the basal quartzites up to 

 the horizon of the Eilean Dubh limestones (Group II. of vertical 

 section of Durness limestones), have been traced for a distance of nearly 

 60 miles with very small variations in their respective thicknesses. 



2. Subdivision of the " Pipe-Bock " Zone. 



The detailed mapping of the Assynt region and the tract 

 north to Ben Arkle has enabled us still further to subdivide the 

 " Pipe-Rock " zone of the quartzites into five horizons. At the top 

 of the fourth subzone (see vertical Section II. p. 406) an interesting 

 discovery was made of a thin band containing Serpulites (like 

 those in the Serpulite-grit) on Ben Arkle. This band, however, 

 seems to be local ; for though it has been carefully searched for 

 to the south, it has not yet been met with. 



The lowest group of Limestones (Group I., vertical section of 

 Durness Limestone) has been also subdivided into eight zones, which 

 have been of the greatest service in unravelling the complicated 

 structure of the limestone plateau at Inchnadamff. A recent 

 examination of the representatives of this group in Eriboll has 

 proved their occurrence in that region also. 



In order to compare the vertical section of strata at Durness and 

 Eriboll with that along the line of complicated structure from 

 Loch More to UUapool, we have drawn out a vertical table of the 

 strata in the latter region (vertical Section II. p. 406), showing the 

 various subdivisions and the horizons of the numerous sheets and 

 dykes of intrusive rocks in Assynt. 



