NORTH SCOTLAND 561 



The northern development, found in the northwest of Scotland, is 

 totally different from the southern, for mudstones are rare or lacking, and 

 the lithic development comprises sandstones and limestones or dolomites. 

 The faunas are wholly distinct from those of the southern area, this dis- 

 tinction being expressed not only in specific, but far more pronouncedly 

 in generic, differences. 



THE NORTHERN SECTIONS 



I have studied these formations at various localities in the northwest 

 of Scotland, especially in the vicinity of Durness, and along the rugged 

 shores of Loch Eriboll. The series begins with a great quartzite, gen- 

 erally of pure quartz grains, though the lower part contains much feld- 

 spar, while the base consists of a thin conglomerate of coarse and fine 

 fragments. The rock rests either on the old Lewisian gneiss, from the 

 disintegration and decomposition of which the quartzite has been derived, 

 or on an intervening sandstone and conglomerate, the Torridonian, which 

 itself is an earlier, terrestrial derivative from the gneiss. 



The total thickness of the basal, sandy, or quartzite series is almost 

 600 feet. The lower third is cross-bedded and feldspathic, and without 

 fossils, representing a purely terrestrial accumulation. The upper two- 

 thirds is more or less fossiliferous and may represent, in part at least, a 

 seashore accumulation. It abounds in vertical worm-holes, mostly of the 

 types referable to Scolithus, from which a part of the rock received its 

 name of "pipe-rock." The upper part becomes more calcareous, and 

 Salterella, Hyoiithes, and Olenellus make their appearance. This portion 

 represents the Lower Cambric division, the fauna being of the Pacific 

 type and like that of the Appalachian trough of North America. The 

 entire series is generally spoken of as the Eriboll quartzite series, from its 

 excellent development on the shores of Loch Eriboll. Through the cal- 

 careous zones the series grade upward into a pure dolomitic limestone, 

 which goes under the name of the Durness limestone series, from the fine 

 exposures found in the vicinity of that village in northwestern Scotland. 

 The lower part of this calcareous series is conformable with the under- 

 lying sandstones, with which it forms a continuous depositional unit. 

 The total thickness of this calcareous series is almost 1,500 feet, and it is 

 divisible into the several following groups : 



Durness limestone series, 1,500 feet: 



VII. Durine group. 

 VI. Croisaphuill group. 



V. Balnakiel group. 

 IV. Sangomore group. 



