Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 13, 2025
Under the same head is an interesting essay upon Glaciers, with figures, one of which is a reduced copy of a sketch in Agassiz's great work, representing the Glacier of Zermatt, in the Monte-Rosa region. Under the head of Heat as an Agent, we have, as might be expected, interesting and valuable matter upon volcanic phenomena, and those of metamorphism.
Early stages of metamorphism are seen in SLATE. Pressure has hardened the marine muds, the arkose, or the volcanic ash from which slates are derived, and has caused them to cleave by the rearrangement of their particles. Under somewhat greater pressure, slate becomes PHYLLITE, a clay slate whose cleavage surfaces are lustrous with flat-lying mica flakes.
The spaces between the grains, which are intact, are filled with a confused mass of peripherally granulated minerals, in which strain shadows are very prominent. The rock has been derived by dynamic metamorphism from a basic igneous rock. 4-Biotite Granite Gneiss. Eighteen miles above mouth of Nascaupee River. A fine-grained rock of gneissic structure having a faint pink color.
There are certain parts in most countries, and particularly in Ireland, where masses of vegetation have undergone a still further stage in metamorphism, namely, in the well-known and famous peat-bogs. Ireland is par excellence the land of bogs, some three millions of acres being said to be covered by them, and they yield an almost inexhaustible supply of peat.
The materials of such strata, if they underwent metamorphism, would be subject to chemical laws, simple and uniform in their action, the same in every climate, and wholly undisturbed by mechanical and organic causes.
The metamorphism is more striking in the first change than in the second. Granted that the soul is immaterial, and that it leaves the body after death, what is there to keep it on earth? Gravitation cannot affect it.
The attitude and structure of the strata tell also of the foldings and fractures, the deformation and the metamorphism, which they have suffered; and the igneous rocks associated with them as lava flows and igneous intrusions add other details to the story. Each formation is thus a separate local chapter in the geological history of the earth, and its strata are its leaves.
Sandstone may be converted into quartzite, and shale into ARGILLITE, a compact, massive clay rock. New minerals may also be developed. Where the changes are most profound, rocks may be wholly made over in structure and mineral composition. In contact metamorphism, thin sheets of molten rock produce less effect than thicker ones.
Under the microscope it is a confused mass of finely granulated minerals, with numerous included crystals. The rock has undergone complete metamorphism and its origin is unknown. 8 Phyllite-Near Otter Lake. A soft extremely fine grained gray rock, with a well developed schistose structure, carrying much magnetite, plagioclase, orthoclase and their alteration products.
CONTACT METAMORPHISM. Rocks beneath a lava flow or in contact with igneous intrusions are found to be metamorphosed to various degrees by the heat of the cooling mass. The adjacent strata may be changed only in color, hardness, and texture. Thus, next to a dike, bituminous coal may be baked to coke or anthracite, and chalk and limestone to crystalline marble.
Word Of The Day
Others Looking