Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 24, 2025
The 'Globigerina' of the Atlantic soundings is identical with that which occurs in the chalk; and the casts of lower silurian 'Foraminifera', which Ehrenberg has recently described, seem to indicate the existence at that remote period of forms singularly like those which now exist.
There is one other geological term, bequeathed to us by a great authority, and which cannot be changed for the better: I mean that of Geological Horizon, applied by Humboldt to the whole extent of any one geological division, as, for instance, the Silurian horizon, including the whole extent of the Silurian epoch.
The mountain-ridges consist of quartz, and the lower country of clay-slate and sandstone, the latter containing Palaeozoic fossils. These fossils have been separately described by Messrs. Morris and Sharpe: some of them resemble Silurian, and others Devonian forms.
As almost all the species either feed on some vegetable substances in growth or decay, or else live upon other insects, some such provision of food was necessary for them. Remains of such plants were discovered in the Silurian rocks. In the Devonian formations, which contain the next oldest set of fossil insects, numbers of conifers and ferns are found.
Moreover, we find through the researches of Messrs. Hartt and Scudder that there were highly developed insects, such as May flies, grasshoppers, etc., in the Devonian rocks of New Brunswick, leading us to expect the discovery of low insects even in the Upper Silurian rocks.
A summer shower carries the soil of my side-hill, which is mainly disintegrated Silurian rock and shale, into the river, and some millions of years hence, when it has become stratified rock, and been lifted up into the light of day, some other, and, I trust, wiser husbandman, will be gathering his harvest from it, and be worried over the downpour that robs him of it.
That they constitute a series of rocks intermediate in date between the lowest Carboniferous and the uppermost Silurian is not disputed by the ablest geologists; and it can no longer be contended that the Upper, Middle, and Lower Old Red Sandstone preceded in date the three divisions to which, by aid of the marine shells, the Devonian rocks have been referred, while, on the other hand, we have not yet data for enabling us to affirm to what extent the subdivisions of the one series may be the equivalents in time of those of the other.
M. Barrande, author of an admirable work on the Silurian rocks of Bohemia, confirms the doctrine of their metamorphosis, having traced more than twenty species through different stages of growth from the young state just after its escape from the egg to the adult form.
Blake has made fine colored drawings of it, which may be published at some future time. . .The family of the Pleurotomariae numbers between four and five hundred fossil species, beginning in the Silurian deposits, but especially numerous in the carboniferous and jurassic formations. The sponges afford another interesting case.
As to fossil representatives of the ichthyic type, the most ancient were not supposed before 1838 to be of a date anterior to the Coal, but they have since been traced back, first to the Devonian, and then to the Silurian rocks.
Word Of The Day
Others Looking