Gradually coming to occupy definite beds, which are deepened and polished by the friction, they impress a characteristic appearance on the land, which guides them as they traverse it, and, although the ice melts at lower levels, vast quantities of clay and broken stones are brought down and deposited in terminal moraines where the glacier ends.
Glaciation was formerly much more extensive, old moraines being observed down to 12,000 ft.
The presence of enormous glaciers in the Ice Age is attested by the moraines at the Atlantic end, and by other indications farther east.
Numerous glacial marks, however, such as polished striated rocks, moraines, erratic blocks, &c., prove that the whole of Greenland, even the small islands and skerries outside the coast, has once been covered by the inland ice.
Nor is there any sign of moraines, glacier-scorings or other traces of the ice-age.
Its front rested on Staten Island and Long Island, whose surface features, and a part of whose area, are due to the deposits along the ice front, including terminal moraines and outwash gravel plains.
As the ice receded, it halted at various points, forming moraines and other glacial deposits.
Heavy terminal moraines and outwashed fluviatile plains have been laid on the cuesta remnants, increasing their height as much as 100 ft.
The great ice sheets formed terminal moraines around their border at various halting stages; but the morainic belts are of small relief in comparison to the great area of the ice; they rise gently from the till plains to a height of 50, 100 or more feet; they may be one, two or three miles wide; and their hilly surface, dotted over with boulders, contains many small lakes in basins or hollows, instead of streams in valleys.
The morainic belts are arranged in groups of concentric loops, convex southward, because the ice sheets advanced in lobes along the lowlands of the Great Lakes; neighboring morainic loops join each other in re-entrants (north-pointing cusps), where two adjacent glacial lobes came together and formed their moraines in largest volume.
The moraines are of too small relief to be shown on any maps but those of the largest scale; yet small as they are, they are the chief relief of the prairie states, and, in association with the nearly imperceptible slopes of the till plains, they determine the course of many streams and rivers, which as a whole are consequent upon the surface form of the glacial deposits.
Nearer the Great Lakes the till sheets are trenched only by the narrow valleys of the large streams; marshy sloughs still occupy the faint depressions in the till plains, and the associated moraines have abundant small lakes in their undrained hollows: hence these drift sheets are of late Pleistocene origin.
South-western Wisconsin and parts of the adjacent states of Illinois, Iowa and Minnesota are known as the driftless area, because, although bordered by drift sheets and moraines, it is free from glacial deposits.
In this central region, however, it is only by way of exception that the cirques were so far enlarged by retrogressive glacial erosion as to sharpen the preglacial dome-like summits into acute peaks; and in no case did glacial action here extend down to the plains at the eastern base of the mountains; but the widened, trough-like glaciated valleys frequently descend to the level of the elevated intermont basins, where moraines were deployed forward on the basin floor.
The finest examples of this kind are the moraines about Jackson Lake on the basin floor east of the Teton Range (Grand Teton, 13,747 ft.), a superb north-south range which lies close to the meridional boundary line between Wyoming and Idaho.
Glacial erosion has been potent in excavating great cirques and small rock-basins, especially among the higher southern surmounting summits, many of which have been thus somewhat reduced in, height while gaining an Alpine sharpness of form; some of the short and steep canyons in the eastern slope have been converted into typical glacial troughs, and huge moraines have been laid on the desert floor below them.
The principal terminal moraines are associated with the ice of the Wisconsin epoch.
Terminal moraines at the border of the Illinoian drift are generally feeble, though widely recognizable, and such moraines at the margin of the Iowan and Kansan drift sheets are generally wanting.
While these ancient events shaped the topography in a broad way, its final development was comparatively recent, during the glacial period, when the loose materials were scoured from some regions and spread out as boulder clay, or piled up as moraines in others; and the original water-ways were blocked in many places.
All the glaciers are now in retreat, with old tree-covered moraines, hundreds or thousands of feet lower down the valley.
Local moraines are found in some of the valleys in Pomona and Hoy.
Considerable interest attaches to the diamonds found in Wisconsin, Michigan and Ohio near the Great Lakes, for they are here found in the terminal moraines of the great glacial sheet which is supposed to have spread southwards from the region of Hudson Bay; several of the drift minerals of the diamantiferous region of Indiana have been identified as probably of Canadian origin; no diamonds have however yet been found in the intervening country of Ontario.
Covering the higher parts of the south-western Palaeozoic area in most places are rolling hills of boulder clay or stony moraines; while the lower levels are plains gently sloping toward the nearest of the Great Lakes and sheeted with silt deposited in more ancient lakes when the St Lawrence outlet was blocked with ice at the end of the glacial period.
- small sheets of water ponded back by some of the last moraines shed by the retreating glaciers - are confined to the more mountainous tracts.
Moraines of the last of the glaciers are numerous throughout the Highlands.
In the mountains west of Kabul glaciers have retired, leaving the moraines perfectly undisturbed.
Cirques, valley troughs, numberless beautiful cascades, sharpened alpine peaks and ridges, glacial lakes, and valley moraines offer everywhere abundant evidence of glacial action, which has modified profoundly practically all the ranges.
Some of them are relics of the longitudinal moraines of the ice-sheet, and they run north-west to south-east, parallel to the striation of the rocks and to the countless parallel troughs excavated by the ice in the hard rocks in the same direction; while the Lojo As, which runs from HangOudd to Vesi-jarvi, and is continued farther east under the name of Salpausellia, parallel to the shore of the Gulf of Finland, are remainders of the frontal moraines, formed at a period when the ice-sheet remained for some time stationary during its retreat.
When the climate became less severe the ice slowly receded, leaving its moraines, called in Sweden krosstenslera and krosstensgrus.
In connexion with almost all the Himalayan glaciers of which precise accounts are forthcoming are ancient moraines indicating some previous condition in which their extent was much larger than now.
In the east these moraines are very remarkable, extending 8 or io m.
They are hemmed in and separated by snowcapped mountain peaks and ridges, which are seamed with glaciers terminating in moraines and shingle slopes at the base of the foot-hills.