United States or Norfolk Island ? Vote for the TOP Country of the Week !
Not only carbonate of lime, but also free carbonic acid gas, is given off plentifully from the soil and crevices of rocks in regions of active and spent volcanoes, as near Naples and in Auvergne. By this process, fossil shells or corals may often lose their carbonic acid, and the residual lime may enter into the composition of augite, hornblende, garnet, and other hypogene minerals.
In a depression of the granitic or hypogene rocks in the States of Massachusetts and Connecticut strata of red sandstone, shale, and conglomerate are found, occupying an area more than 150 miles in length from north to south, and about five to ten miles in breadth, the beds dipping to the eastward at angles varying from 5 to 50 degrees.
The anthracite and plumbago associated with hypogene rocks may have been coal; for not only is coal converted into anthracite in the vicinity of some trap dikes, but we have seen that a like change has taken place generally even far from the contact of igneous rocks, in the disturbed region of the Appalachians.
Relation of trappean Rocks to the Products of active Volcanoes. Section through formations from a, low, to c, high. a. Hypogene formations, stratified and unstratified. b. Aqueous formations. c. The aqueous or fossiliferous rocks having now been described, we have next to examine those which may be called volcanic, in the most extended sense of that term.
But if we investigate different mountain chains, we find gneiss, mica-schist, hornblende-schist, chlorite-schist, hypogene limestone, and other rocks, succeeding each other, and alternating with each other in every possible order.
Imperfection of the Record. Calcaire Silicieux. Gres de Beauchamp. Calcaire Grossier. Miliolite Limestone. Soissonnais Sands. Lower Eocene of France. Nummulitic Formations of Europe, Africa, and Asia. Eocene Strata in the United States. Gigantic Cetacean. Map of the principal Eocene areas of North-western Europe, showing: Shaded dotted: Hypogene rocks and strata older than the Devonian.
Here, therefore, if anywhere, we might expect to find hypogene formations of Eocene date breaking out in the central axis or most disturbed region of the loftiest chain in Europe. Accordingly, in the Swiss Alps, even the flysch, or upper portion of the nummulitic series, has been occasionally invaded by Plutonic rocks, and converted into crystalline schists of the hypogene class.
When it alternates with these rocks, it often contains some crystals of mica, and occasionally quartz, feldspar, hornblende, talc, chlorite, garnet, and other minerals. It enters sparingly into the structure of the hypogene districts of Norway, Sweden, and Scotland, but is largely developed in the Alps.
There is certainly a great and striking general resemblance in the principal kinds of hypogene rocks in all countries, however different their ages; but each of them, as we have seen, must be regarded as geological families of rocks, and not as definite mineral compounds.
The more ordinary or regular veins are usually worked in vertical shafts, and have evidently been fissures produced by mechanical violence. They traverse all kinds of rocks, both hypogene and fossiliferous, and extend downward to indefinite or unknown depths. We may assume that they correspond with such rents as we see caused from time to time by the shock of an earthquake.
Word Of The Day