The oldest rocks, the gneisses and schists of the Archean period, form nearly the whole of the Central Plateau, and are also exposed in the axes of the folds in Brittany.
They consist for the most part of red and grey gneisses and granulites, with subordinate layers of granite and granitite.
The difference between schists and gneisses is mainly that the latter have less highly developed foliation; they also, as a rule, are more coarse grained, and contain far more quartz and felspar, two minerals which rarely assume platy or acicular forms, and hence do not lead to the production of a fissile character in the rocks in which they are important constituents.
It is often taught that gneisses are the further stages of the crystallization of schists and belong to a deeper zone where the pressures and the temperatures were greater.
Practically all the remaining area in these islands is occupied by metamorphic schists and gneisses which occur in great variety and with which are associated numerous dikes and masses of intrusive igneous rock.
The metamorphic rocks of the rest of Mainland are principally coarse gneisses, micaceous and chloritic schists, quartzites, &c.; in these rocks at Tingwall and Wiesdale considerable beds of limestone occur, which may be followed across the island in a northerly direction to Yell Sound, and to Dales Voe in Delting.
-) Gneisses, Schists, Marbles, Granites (Swaziland Series).
In the Umzimkulu river and in the Tugela river below its junction with the Buffalo, metamorphic limestones are associated with schists, gneisses and granites.
The plateau is built up of granites, gneisses and crystalline schists of Archean and probably Primary age.
The oldest rocks in the country are the granites, gneisses, &c., of the southern massif and the crystalline schists which form the axis of the Cordillera and the Caribbean chain.
In the nature and position of the upland rocks - mainly crystalline schists and gneisses, excessively complicated and disordered in mass, and also internally deformed - there is found abundant proof that the peneplain is a degraded mountain region.
The Southern Alps, the backbone of the South Island, rest on a foundation of coarse gneisses and schists, that are quite unrepresented in the North Island.
The oldest rocks are Archean, represented by the band of gneisses and schists exposed along the western foot of the Southern Alps.
==Geology== The rocks of the Appalachian belt fall naturally into two divisions; ancient (pre-Cambrian) crystallines, including marbles, schists, gneisses, granites and other massive igneous rocks, and a great succession of Paleozoic sediments.
"Dalradian" schists and gneisses, with some dark limestones, come out in the north-east of the county, forming a moorlandregion between Cushendun and Ballycastle.
Such veins often attain a thickness of several feet, and sometimes possess a columnar structure perpendicular to the enclosing walls; they are met with in the crystalline limestones and other Laurentian rocks of New York and Canada, in the gneisses of the Austrian Alps and the granulites of Ceylon.
The oldest rocks, granites, gneisses and schistose sandstones, the Ngami series, rise to the surface in the east and south-east and doubtless immediately underlie much of the sand areas.
The schists and gneisses of the Ox Mountain axis also enter the county north of Castlebar.
The central zone of crystalline rock consists chiefly of gneisses and schists, but folded within it is a band of Palaeozoic rocks which divides it longitudinally into two parts.
The oldest rocks, forming the greater mass of the hinterland, are gneisses, schists and granites of Archaean age.
It is not possible to say what was the original character of many of the disrupted materials, for they have been rearranged and re-crystallized into granulitic, flaggy gneisses and schists (Moine schists).
The fundamental rocks of the island are gneisses, through which cut the feldspathic granites which form the Haghier massif.
The natural history of Sokotra, unravelled by the study of its geology and biology, has been summarized by Professor Balfour as follows: "During the Carboniferous epoch there was in the region of Sokotra a shallow sea, in which was deposited, on the top of the fundamental gneisses of this spot, ...
On the mainland, the north and east shores are of gneisses and granites of archaean age, with a broken and hilly surface rising in places to 600 ft.
The oldest rocks in New South Wales are referrable to the Archean system, and consist of gneisses and schists, including the glaucophane-schists in the New England tableland, and hornblendeschists of Berthong.
PreCambrian rocks are represented by the gneisses of Primrose Hill and schists of Rushton in Shropshire; by the gneisses forming the core of the Malvern Hills, and by the ancient volcanic and other rocks of the Wrekin, Charnwood Forest and Nuneaton.
The basin in which these sandstones were laid down is limited on the east by ancient gneisses and schists overlain by the highly inclined red felspathic grits.
Gneisses, schists, slaty rocks.
It is also a common constituent, as irregular grains, in many gneisses and crystalline schists, a quartz-schist being composed largely of quartz.