Lower Cretaceous limestones and schists, with radiolarian cherts, are extensively developed; and in many parts of the island Upper Creta 1 See L.
In the extreme north-east are found the oldest rocks in the state - lower Devonian (the New Scotland beds of New York) and, not so old, an extension of the Lower Carboniferous which underlies the Warrior coalfields of Alabama, and which consists of cherts, limestones, sandstones and shales, with a depth of 800 to 900 ft.
Radiolaria are found in cherts in the Culm of Devonshire and Cornwall, in Russia, Germany and elsewhere.
In descending order they embrace the following subdivisions, whose thickness in the district of Durness is estimated at about 2000 ft.: (e) limestones, dolomites and cherts, with numerous organic remains; (d) grit and quartzite, with Saltarella and Olenellus (Serpulite Grit); (c) calcareous shales and dolomites, with many annelid casts and sometimes Olenellus (Fucoid Beds); (b) Upper Quartzite, often crowded with annelid pipes (Pipe Rock Quartzite); (a) Lower Quartzite - their original upper limit can nowhere be seen, for they have been overridden by the Eastern Schists in those gigantic underground disturbances already referred to, by which these rocks, the Archean gneiss and Torridonian sandstone, were crumpled, inverted, dislocated and thrust over each other.
On the east side in North Glen Sannox Burn, they are associated with cherts, grits and dark schists with pillowy lavas, tuffs and agglomerates which, on lithological grounds, have been regarded as probably of the same age as the Arenig cherts and volcanic rocks in the south of Scotland.