Glaciation was formerly much more extensive, old moraines being observed down to 12,000 ft.
These afford the clearest evidences of glaciation on a great scale in early Carboniferous times.
of the Urals, but the question as to the glaciation of the Urals still remains open.
They almost invariably lie on strongly ice-worn platforms of rock, and are obviously hollows produced by the gouging action of the sheets of land-ice by which the general glaciation of the country was affected.
The unusual glaciation of the east coast is evidently owing to the north polar current carrying the ice masses from the north polar basin 4 south-westward along the land, and giving it an entirely arctic climate down to Cape Farewell.
The effect of glaciation on the soil is noted in a later paragraph.
It is most probable that, when allowance has been made for the obliteration of glacial markings, and the region has been better explored, it will appear that the glaciation of Turkestan was on a scale at least as vast as that of the Himalayas.
The reason for this exemption from glaciation is the converse of that for the southward convexity of the morainic loops; for while they mark the paths of greatest glacial advance along lowland troughs (lake basins), the driftless area is a district protected from ice invasion by reason of the obstruction which the highlands of northern Wisconsin and Michigan (part of the Superior oldland~ offered to glacial advance.
Glacial deposits certainly do exist in the Permo-carboniferous formations, which are described under that head, but in the true Carboniferous system glaciation may be taken as not proven.
It presents evidences of having been subjected to powerful glaciation, and to subsequent immersion and immense denudation.
Local glaciation has carved the higher levels of this range into a maze of amphitheatres containing lakes, separated from each other by aretes and alpine peaks.
No satisfactory solution of this problem has been reached; but the association of the Great Lakes and other large lakes farther north in Canada with the great North American area of strong and repeated glaciation is highly suggestive.
Outside the region affected by glaciation, deposits by wind, rain, rivers, &c., have been building up the land, and sedimentation has N ~ been in progress in lakes and about coasts.
The few small lakes of the state are mostly on the Pocono plateau, where they were formed by glaciation; here, too, are some streams with picturesque cascades.
Local glaciation has modified the higher levels of the Bighorn Mountains, giving glacial cirques, alpine peaks and many mountain lakes and waterfalls.
North of the morainic belt the effect of the glaciation is seen in the irregular courses of the streams, the numerous lakes and freshwater marshes and the falls and rapids along those streams displaced by the glaciers from their former courses.
The glaciation is also responsible for the poor soil of most of the state, for, although the rocks are the same crystallines which give good soils further south in unglaciated regions, all the decayed portions of the Maine rocks have been removed by glacial erosion, revealing fresh, barren rock over great areas, or depositing the rather sterile hard-pan as a thin coating in other places.
On some of these peaks again there is a considerable amount of glaciation, more particularly on the slopes of Diklos-mta, where the glaciers descend to 7700 ft.
Glaciation.-In the central and western parts of the Tian-shan there exist numerous indications of former glaciation on an extensive scale, e.g.
The glacial deposits profoundly modified the surface of the country, whether they resulted from the melting of the ice-sheets of the time of maximum glaciation, or from the movements of local glaciers.
Preserved in the formation known as the Dwyka Conglomerate, are evidences that at this time the greater portion of South Africa was undergoing extreme glaciation, while the same conditions appear to have prevailed in India Table Of Formations Sedimentary.
In the United States no direct evidence has been found of the low tensperaturewhich brought about glaciation in many other parts of the earth during this period.
(The causes or conditions of glaciation, it may be noted here, are no better known than in 1910.
The process of disintegration and levelling down has reached such an advanced stage that, if ever there did exist evidences of former glaciation, they have now become entirely obliterated, even to the complete pulverization of the erratic blocks, supposing there were any.
All the lakes of the state were formed by glaciation.
the mountains of which appear to have escaped glaciation.
Many of them are at high elevations (Lake Victoria, 13,400 ft., being probably the most elevated), and are undoubted vestiges of an ancient period of glaciation.
Since the uplift and stream dissection a slight depression has allowed the sea to invade the lower portions of the river valleys, forming the bays known as Narragansett Bay, Providence "river," Sakonnet " river," &c. Glaciation has disturbed the river 1 Block Island, over which the jurisdiction of the state extends, lies Jo m.
The northern half is more broken and irregular; elevations, usually rounded, mingle with depressions some of which are occupied by small shallow lakes or ponds, the characteristic physical features of this region being due to glaciation.
Much interest attaches to estimates of time based on data afforded by the consequences of glaciation.
Much of the grandest scenery is due to glaciation.
After the uplift which caused the rivers to cut below the general " uplands," and develop well marked valleys for themselves, came the period of the great continental glaciation.
northern summer insolation was unusually low at the onset of the last glaciation around 115,000 years ago, it was high during deglaciation.
microcrystalline assemblages are more probably the product of geologically recent alteration, post-dating the last glaciation.
We continued to climb and reached a tarn formed by glaciation.
The forms of Vermont's mountains, even to the highest summits, were to a great extent rounded by glaciation, but as the rocks vary much in texture and are often steeply inclined, stream erosion has cut valleys deep and narrow, often mere gorges.
It has been suggested, however, that a prolonged period of volcanic activity may reduce the air temperature to a marked degree by throwing large quantities of dust into the atmosphere: this will act by preventing the penetration of solar radiation.) During a period of prolonged glaciation water becomes withdrawn from the ocean, for rainfall goes to form solid ice-caps that accumulate upon polar and continental land areas.
These irregular features are wanting south of the limits of Pleistocene glaciation; there the rivers have had time, in the latest cycle of erosion into which they have entered, to establish themselves in a continuous flow, and as a rule to wear down their courses to a smoothly graded slope.
Glaciation has strongly scoured away the deeply-weathered soils that presumably existed here in preglacial time, revealing firm and rugged ledges in the low hills and swells of the ground, and spreading an irregular drift cover over the lower parts, whereby the drainage is often much disordered; here being detained in lakes and swamps (muskegs) and there rushing down rocky rapids.
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