The Archean rocks have a broad extension in Finland, N.
Both to the east and to the west of this depression the Archean and Palaeozoic rocks which form the greater part of the island are strongly folded, with the exception of the uppermost beds, which belong to the Permian system.
Granite and Archean schists form nearly the whole of the eastern hills from the Strait of Bonifacio southwards to the Flumendosa river, culminating in Monti del Gennargentu.
In the geological history of France there have been two great periods of folding since Archean times.
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.
Australia is essentially the fragment of a great plateau land of Archean rocks.
It consists in the main of an Archean block or " coign,"which still occupies nearly the whole of the western half of the continent, outcrops in north-eastern Queensland, forms the foundation of southern New South Wales and eastern Victoria, and is exposed in western Victoria, in Tasmania, and in the western flank of the Southern Alps of New Zealand.
These areas of Archean rocks were doubtless once continuous.
But they have been separated by the foundering of the Coral Sea and the Tasman Sea, which divided the continent of Australia from the islands of the Australasian festoon; and the foundering of the band across Australia, from the Gulf of Carpentaria, through western Queensland and western New South Wales, to the lower basin of the Murray, has separated the Archean areas of eastern and western Australia.
The breaking up of the old Archean foundation block began in Cambrian and Ordovician times.
The sea does not appear to have extended completely across Australia, breaking it into halves, for a projection from the Archean plateau of Western Australia extended as far east as the South Australian highlands, and thence probably continued eastward, till it joined the Victorian highlands.
Ungava includes much of the lower portion of Labrador, with a rim of recent marine deposits along its western coast, but the interior has the usual character of low rocky hills of Archean rocks, especially granite and gneiss, with a long band of little disturbed iron-bearing rocks, resembling the Animikie, or Upper Huronian of the Lake Superior region, near its eastern side.
In the early part of the Palaeozoic era only the gneissic region of Finland and Olonets and probably the Archean mass of S.
The Ordovician and Silurian systems are widely developed, and it is most probable that, with the exception of the Archean continents of Finland and the S, the sea covered the whole of Russia.
Here the folded Archean rocks are overlaid by Cambrian and Ordovician beds, which still lie for the most part flat and undisturbed.
South and east of the Palaeozoic plateau is an extensive area consisting chiefly of Archean rocks, and including the greater part of Mongolia north of the Tian-shan.
There is again a floor of folded Archean rocks overlaid by nearly horizontal strata of Lower Palaeozoic age; but these are followed by marine beds belonging to the Carboniferous period.
Large ore-bodies of granular and compact magnetite occur as beds and lenticular masses in Archean gneiss and crystalline schists, in various parts of Norway, Sweden, Finland and the Urals; as also in the states of New York, New Jersey, Pennsylvania and Michigan, as well as in Canada.
Bitumen is, in its various forms, one of the most widel y -distributed of substances, occurring in strata of every geological age, from the lowest Archean rocks to those now in process of deposition, and in greater or less quantity throughout both hemispheres, from Spitzbergen to New Zealand, and from California to Japan.
In the southern region, which is by far the better known, the oldest rocks are granites, crystalline schists and other rocks of Archean aspect.
The plateau is built up of granites, gneisses and crystalline schists of Archean and probably Primary age.
- Geologically Venezuela consists of three distinct regions: (1) South of the Orinoco a great mass of granite, gneiss, pyroxenite and other crystalline rocks, continuous with that of Guiana and probably of Archean age.
- Speaking generally, New Caledonia may be described as a band of Palaeozoic and probably Lower Palaeozoic rocks, associated doubtless with some Archean beds; this band runs from north-west to south-east, through the whole length of the island.
This foundation consists of Archean, Palaeozoic and Mesozoic beds folded together, the direction of the folds being N.
Archean rocks - gneiss, schist and granite - cover large areas through which the Nile cuts its way in alternate narrow gorges and open reaches.
In Ankole and Koki rocks consisting of granular quartzite, schistose sandstone, red and brown sandstone, and shales with cleaved killas rest on the Archean platform and possibly represent the Lower Witwatersrand beds of the Transvaal.
The oldest rocks are Archean, represented by the band of gneisses and schists exposed along the western foot of the Southern Alps.
It has been suggested that the, jasperoids and diabases of the Tarawera Mountains on the North Island may be of Upper Archean age, from their resemblance to the Heathcotian rocks of Australia.
The higher elevations are mostly either Archean or Paleozoic formations projecting above Tertiary deposits.
Rocks of Archean and Palaeozoic ages contribute only a small share, but there is a Scale, 1:7,700,000 English Miles o 60 80 too 200 ï¿½-' 4,, ,% 4s o,r^ ° o ?
Archean rocks form the cores of the ancient crystalline masses within the littoral zone from Algiers to Bona.
1.2.1 Archean Rocks 1.2.2 Eastern or Younger Schists 1.2.3 Torridonian Sandstone 1.2.4 Cambrian 1.2.5 Ordovician and Silurian 1.2.6 Old Red Sandstone 1.2.7 Carboniferous 1.2.8 Permian 1.2.9 Triassic 1.2.10 Jurassic 1.2.11 Cretaceous 1.2.12 Older Tertiary 1.2.13 Post-Tertiary 1.2.14 Recent
Dispersed over all parts of the western Highlands, they are most numerous in the north-west, especially in the Outer Hebrides and in the west of the shires of Ross and Cromarty and Sutherland, where the surface of the Archean gneiss is so thickly sprinkled with them that many tracts consist nearly as much of water as of land.
High have been cut out of the Archean gneiss.
Archean gneiss, Cambrian sandstone, Silurian quartzite, limestone and schist, Jurassic sandstone and limestone, Cretaceous sandstone, and Tertiary basalts, gabbros, and granitic rocks all enter into the composition of the islands.
Archean System >>
Timor consists of a core of ancient rocks (Archean?) upon which rest Permian and later deposits of sedimentary origin.
In Quebec the chief portion is south of the St Lawrence on the low plain extending from Montreal to the mountains of the " Eastern Townships," while in Ontario it extends from the Archean on the north to the St Lawrence and Lakes Ontario, Erie and Huron.
Georgian Bay and the northern part of Lake Huron with the whole northern margin of Lake Superior bathe the foot of the Laurentian plateau, which rises directly from these lakes; so that the older fertile lands of the country with their numerous cities and largely-developed manufactures are cut off by an elevated, rocky and mostly forest-covered tract of the Archean from the newer and far more extensive farm lands of the west.
- Passing westward by rail from the forest-covered Archean with its rugged granite hills, the flat prairie of Manitoba with its rich grasses and multitude of flowers comes as a very striking contrast, introducing the Interior Continental plain in its most typical development.
This great plain runs north-westward between the border of the Archean protaxis and the line of the Rocky Mountains, including most of Manitoba, the southern part of Saskatchewan and most of Alberta.
This interior plain of the continent represents the area of the ancient sea by which it was occupied in Mesozoic times, with a more ancient margin towards the north-west against the Archean, where undisturbed limestones and other rocks of the Silurian and Devonian rest upon the downward slope of the Laurentian Shield.