United States or New Caledonia ? Vote for the TOP Country of the Week !
In what manner then did the great lake-basins originate if they were not hollowed out by ice? My answer is, they are all due to unequal movements of upheaval and subsidence.
As the fine mud is carried away by a river from the deep pool which is formed from the base of every cataract, so it seems to be imagined that lake-basins may be gradually emptied of the mud formed by abrasion during the glacial period.
The carpenters who came to build our frame house, noticing how the sedges sunk beneath their feet, said that if they should break through, they would probably be well on their way to California before touching bottom. On the contrary, all these lake-basins are shallow as compared with their width. When we went into the Wisconsin woods there was not a single wheel-track or cattle-track.
Subsequently to the retreat of the great glaciers we know that the lake-basins have been to a certain extent encroached upon and turned into land by river deltas; one of which, that of the Rhone at the head of the Lake of Geneva, is no less than 12 miles long and several miles broad, besides which there are many torrents on the borders of the same lake, forming smaller deltas.
It is impossible to deny that the mere geographical distribution of lakes points to the intimate connection of their origin with the abundance of ice during a former excess of cold, but how far the erosive action of moving ice has been the sole or even the principal cause of lake-basins, is a question still open to discussion.
We may easily conceive that a similar mass might now be produced, if a copious evolution of gases should occur in one of the lake-basins. If a breach should be made in the side of the cone, the flood would sweep away great heaps of ejected fragments of shale and sandstone, which would be borne down into the adjoining valleys.
Following up this idea after he had visited Switzerland and without any communication with M. de Mortillet or cognisance of his views, he suggested in 1859 that the lake-basins were not of pre-glacial date, but had been scooped out by ice during the glacial period, the excavation having for the most part been effected in Miocene sandstone, provincially called, on account of its softness, "molasse."
Extinct Glaciers of Switzerland. Alpine Erratic Blocks on the Jura. Not transported by floating Ice. Extinct Glaciers of the Italian Side of the Alps. Theory of the Origin of Lake-Basins by the erosive Action of Glaciers considered. Successive phases in the Development of Glacial Action in the Alps. Probable Relation of these to the earliest known Date of Man.
La Proprieta Fondiaria, etc., p.144. The quantity of water escaping from the lakes by infiltration depends much on the hydrostatic pressure on the bottom and the walls of the lake-basins, and consequently the depression of the lake surface, diminishing this pressure, would diminish the infiltration. Mountain Lakes.
When, however, the period of upheaval was followed by one of gradual subsidence, the movement not being everywhere strictly uniform, lake-basins would be formed wherever the rate of depression was in excess in the upper country.
Word Of The Day