Vietnam or Thailand ? Vote for the TOP Country of the Week !
This dissimilarity is the more striking, considering that these two parallel chains are separated by a plain only between ten and fifteen miles in width; and that the Uspallata lavas, as well as no doubt the alternating tufaceous beds, have proceeded from the west, from points apparently between the two ranges.
Here numerous proofs are seen of submarine eruptions, by which the argillaceous and sandy strata were invaded and cut through, and tufaceous breccias formed. Inclosed in these breccias are many angular and hardened fragments of laminated clay in different states of alteration by heat, and intermixed with volcanic sands. View of the Isle of Cyclops, in the Bay of Trezza.
It is supposed by the Duke of Argyll that this formation was accumulated in a shallow lake or marsh in the neighbourhood of a volcano, which emitted showers of ashes and streams of lava. The tufaceous envelope of the fossils may have fallen into the lake from the air as volcanic dust, or have been washed down into it as mud from the adjoining land.
Lava-currents have also flowed upon the land and along the bottom of the sea volcanic sand, pumice, and scoriae have been showered down so abundantly that whole cities were buried- tracts of the sea have been filled up or converted into shoals and tufaceous sediment has been transported by rivers and land-floods to the sea.
Although in other parts of Patagonia I have no direct evidence of shoal-water shells having been buried under a great thickness of superincumbent submarine strata, yet it should be borne in mind that the lower fossiliferous strata with several of the same species of Mollusca, the upper tufaceous beds, and the high summit-plain, stretch for a considerable distance southward, and for hundreds of miles northward; seeing this uniformity of structure, I conceive it may be fairly concluded that the subsidence by which the shells at Santa Cruz and S. Julian were carried down and covered up, was not confined to these two points, but was co-extensive with a considerable portion of the Patagonian tertiary formation.
A mixture of lime and clay, a tufaceous deposit, and an apparently recent deposit of soapstone, containing a variety of substances, as alumina, silica, lime, soda, magnesia, and iron.
Tufaceous strata thus formed in the neighbourhood of Vesuvius, Etna, Stromboli, and other volcanoes now in islands or near the sea, may give information of the relative age of these tuffs at some remote future period when the fires of these mountains are extinguished.
The vast quantity of this unworked fuel would be sufficient to warm the whole population of Iceland for a century; this vast turbary measured in certain ravines had in many places a depth of seventy feet, and presented layers of carbonized remains of vegetation alternating with thinner layers of tufaceous pumice.
Section from Illapel to Combarbala; gypseous formation with silicified wood. Panuncillo. Coquimbo; mines of Arqueros; section up valley; fossils. Guasco, fossils of. Copiapo, section up valley; Las Amolanas, silicified wood. Conglomerates, nature of former land, fossils, thickness of strata, great subsidence. Valley of Despoblado, fossils, tufaceous deposit, complicated dislocations of.
It appears from the investigations of Sir R. Murchison in Shropshire, that when the Lower Silurian strata of that country were accumulating, there were frequent volcanic eruptions beneath the sea; and the ashes and scoriae then ejected gave rise to a peculiar kind of tufaceous sandstone or grit, dissimilar to the other rocks of the Silurian series, and only observable in places where syenitic and other trap-rocks protrude.
Word Of The Day