Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 11, 2025
The district around the Laacher See is covered by laminated ejecta of the old volcano, probably of subaërial origin, through which bosses of the fundamental slate peer up at intervals, while the surface is diversified by several truncated cones.
I am almost disposed to doubt whether it is necessary to make the concession of "wet and swampy;" otherwise, there is nothing that I know of to be said against this excellent conspectus of the reasons for believing in the subaërial origin of coal.
Along with this upheaval of the sea-bed there was extensive denudation and erosion of the strata, so that valleys were eroded over the subaërial tracts, and the Jordan-Arabah valley received its primary form and outline.
And if the mean height of all the land now above the sea throughout the globe is 1000 feet, as some geographers believe, it would only require six million years to subject a mass of rock equal in volume to the whole of the land to the action of subaerial denudation.
They are subtended by one of many aqueducts, whose walls, two feet thick, showed no signs of brick: it is remarkable for being run underground to pierce a hillock; in fact, the system is rather Greek or subterranean, than Roman or subaerial. Still descending, we found the ancient or mediaeval wells, numbering about a dozen, and in no wise differing from those of Shuwak.
The horizontal plane of the sea now intersects an old land surface roughened by subaerial denudation. The shore line is irregular and indented in proportion to the relief of the land and the amount of the submergence which the land has suffered. It follows up partially submerged valleys, forming bays, and bends round the divides, leaving them to project as promontories and peninsulas.
The few still active volcanoes in Chile are confined to the central and loftiest ranges of the Cordillera; and volcanic matter, such as appears to have been of subaerial eruption, is everywhere rare. According to Meyen, there is a hill of pumice high up the valley of the Maypu, and likewise a trachytic formation at Colina, a village situated north of St. Jago.
Besides the inland cliffs above alluded to which mark the ancient limits of the sea, there are other abrupt terminations of rocks of various kinds which resemble sea-cliffs, but which have in reality been due to subaerial denudation.
On the banks of the Great River, a section is exposed nearly five hundred feet deep, worn through numerous thin sheets of the lava of this series, which are separated from each other by beds of scoriae. They seem to have been of subaerial formation, and to have flowed from several points of eruption on the central platform, of which the Piton du Milieu is said to be the principal one.
Here extended deposits of peat may accumulate in swamps, and the remains of land and fresh- water animals and plants swept down by the stream are imbedded in the silts laid at times of flood. Borings made in the deltas of great rivers such as the Mississippi, the Ganges, and the Nile, show that the subaerial portion often reaches a surprising thickness.
Word Of The Day
Others Looking