E Arabian Sea Ba Of G A L e Geological information incomplete Desert Deposits Quaternary Tertiary Mesozoic Palaeozoic Archaean and Metamorphic Younger Volcanic Rocks English Miles b iuHi iiiiuiiiiii after llargl,aua Geology The geology of Asia is so complex and over wide areas so little known that it is difficult to give a connected account of either the structure or the development of the continent, and only the broader features can be dealt with here.
There are, it is true, mountain ranges which are formed of folded beds; but in many cases the direction of the chains is different from that of the folds, so that the ranges must owe their elevation to other causes; and the folds, moreover, are of ancient date, for the most part Archaean or Palaeozoic. The configuration of the region is largely due to faulting, trough-like or tray-like depressions being formed, and the intervening strips, which have not been depressed, standing up as mountain ridges.
He wrote Correlation Papers - Archaean and Algonkian (1892), Some Principles Controlling the Deposition of Ores (1901).
- Molengraaff considers the Barberton series to be the metamorphosed equivalent of the Hospital Hill series, while Hatch regards it to be older and to form a portion of his Archaean series (Swaziland schists) to which position it is here assigned.
South and west of the Fossa Magna the beds are thrown into folds which run approximately parallel to the general direction of the coast, and two zones may be recognizedan outer, consisting of Palaeozoic and Mesozoic beds, and an inner, consisting of Archaean and Palaeozoic rocks, with granitic intrusions.
At the southern extremity of the great table-land, however, in the state of Puebla, there is a considerable mass of crystalline rocks which is believed to be of Archaean age.
- The Archaean crystalline rocks abound in deposits of magnetite and red haematite, many of them very large and rich.
The oldest rocks, belonging to the Archaean system, occur in the south, forming the Vosges and the Black Forest in the west, and the greater part of the Bohemian massif, including the Erzgebirge, in the east.
In Saxony also the upper Cretaceous beds rest directly upon the Palaeozoic or Archaean rocks.
Between the Palaeozoic area near Ottawa, and Georgian Bay to the north of the region just referred to, there is a southward projection of the Archaean protaxis consisting of granite and gneiss of the Laurentian, enclosing bands of crystalline limestone and schists, which are of interest as furnishing the only mines of "Old Ontario."
While all the larger cities and most of the manufacturing and farming districts of the province belong to old Ontario, there is now in process of development a "New Ontario," stretching for hundreds of miles to the north and north-west of the region just described and covering a far larger area, chiefly made up of Laurentian and Huronian rocks of the Archaean protaxis.
From Lake Ontario the St Lawrence emerges through the meshes of the Thousand Islands, where it crosses Archaean rocks, after which follow several rapids separated by quieter stretches before Montreal is reached at the head of ocean navigation.
The oldest rocks, forming the greater mass of the hinterland, are gneisses, schists and granites of Archaean age.
The geological formations represented are the following in descending order: Recent or sub-recent Pleistocene Pliocene Miocene Lower Miocene Oligocene and Eocene Upper Cretaceous or Lower Eocene Upper Cretaceous Jurassic or Lower Cretaceous Carboniferous to Trias Archaean The latest movement to which the Gulf has been or is now being subjected is one of gradual elevation, of which traces are found in recent littoral concretes, now as much as 450 ft.
They are known to be pre-Jurassic, but whether they are Palaeozoic or Archaean is uncertain.
From the absence of any well-marked unconformity it is evident that in the northern part of the Himalayan belt, at least in the Spiti area, there can have been no post-Archaean folding of any magnitude until after the deposition of the Nummulitic beds, and that the folding was completed before the later Tertiaries of Hundes were laid down.
The Mongolian or Great Altai, on the other hand, consists mainly of gneiss and Archaean rocks.
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' four topographic belts of the state correspond very closely to the outcrops of its geological formations; the rocks of the Appalachian belt being of Palaeozoic age; the formation of the Highlands, Archaean; that of the Triassic Lowland, Triassic; that of the irregular hills of the Coastal Plain, Cretaceous and Tertiary.
The Western Division is composed entirely of Archaean and Palaeozoic rocks, embracing the whole range from pre-Cambrian up to Carboniferous.
The outcrops of these rocks succeed each other in order of age in roughly concentric belts, with the Archaean mass of the island of Anglesey as a centre, but the arrangement in detail is much disturbed and often very irregular.
The low island of Anglesey, which is built tip of the fundamental Archaean rocks, is important as a link in the main line of communication with Ireland, because it is separated from the mainland by a channel narrow enough to be bridged, and lies not far out of the straight line joining London and Dublin.
Around the western and northern edge of the Old Red Sandstone plain the underlying Silurian rocks (and even the Cambrian and Archaean in places) have been bent up so that their edges form hills of singular abruptness and beauty.
Wenlock Edge, running from south-west to north-east, is an escarpment of Silurian limestone, while the broad upland of Long Mynd, nearly parallel to it on the north, is a mass of Archaean rock.
The remarkable features of the scenery of South Devon and Cornwall are due to a narrow band of Archaean rock which appears in the south of the peninsulas terminating in Lizard Head and Start Point, and to huge masses of granite and other eruptive rocks which form a series of great bosses and dykes.
A few small outcrops occur where still more ancient strata have been raised to the surface, as, for instance, in Charnwood Forest, where the Archaean rocks, with intrusions of granite, create a patch of highland scenery in the very heart of the English plain; and in the Lickey Hills, near Birmingham, where the prominent features are due to volcanic rocks of very ancient date.
The northern portion, lying mainly between io and 15° N., consists of a huge mass of Archaean rocks with a mean height of from 7000 to 7500 ft.