96 STRATIGRAPHICAL GEOLOGY 



faces of bedding planes, and no explanation of them has yet been 

 suggested. 



5. Scotland 



In the north-west of Scotland Cambrian rocks flank the eastern 

 side of the tract occupied by the Hebridean and Torridonian, all 

 the way from Durness and Eriboll on the north coast down to 

 the island of Skye. Before the discovery of Olenellus in these 

 rocks they were supposed to be of Ordovician age. 



In the north of Sutherland there are two tracts of Cambrian, 

 the relative positions of which are shown in Fig. 23. The beds 

 of the Durness area are arranged in the form of a basin truncated 

 on the eastern side by a fault which brings them against the 

 Archaean gneiss ; on the west they are seen to rest unconformably 

 on this gneiss and on the red Torridon sandstone. The Durness 

 basin is separated from that of Loch Eriboll by a prominent ridge 

 of Archaean gneiss, which, however, bears an outlier of the 

 Cambrian basement beds. The Eriboll area exhibits the same 

 series as that of Durness, but they are crushed and faulted in a 

 remarkable manner, and are cut off on the east by a thrust-plane, 

 which carries some of the Archaean gneiss over the Cambrian Series, 

 so that here the ordinary test of age by superposition becomes 

 useless. 



The total thickness of the beds composing the Cambrian System 

 of Scotland is estimated as at least 2000 feet, but the upper limit 

 is not reached, being everywhere concealed beneath the masses of 

 crushed and sheared rock which have been carried westward onto 

 and over the Cambrian strata. The exposed portion is divisible 

 into two series, an arenaceous below and a calcareous series above. 

 These can also be subdivided as follows : 



'3. Grey limestones, some dark and some light grey, with 

 Calcareous many layers of chert ; many fossils throughout. 



Series or 2. Dolomitic limestones, grey, white, mottled, and pink, 

 Durness - with layers of chert nodules. The Sangomore and 



limestone, Sailmhor Groups. Few fossils. 



1400 feet 1. Light-coloured dolomites and limestones, with bands of 



chert. 



: 5. Dolomites and limestones with Salterella. 

 4. Dolomitic grits with Salterella (Serpulite grit) \ 200 

 Arenaceous 3. Calcareous mudstones (Fucoid Beds) / feet. 



Series, \ 2. Fine-grained quartzites perforated by worm burrows 

 720 feet (pipe rock). 300 feet. 



1. Coarse flaggy grits and quartzites, with a basement bed 

 of brecciated conglomerate. 200 feet. 



The most abundant fossils in the Durness limestone are 

 Cephalopoda Orthoceras, Piloceras, and Lituites. Next in number 



