United States or Cameroon ? Vote for the TOP Country of the Week !
MICA SCHIST, the most common of schists, and in fact of all metamorphic rocks, is composed of mica and quartz in alternating wavy folia. All gradations between it and phyllite may be traced, and in many cases we may prove it due to the metamorphism of slates and shales. It is widespread in New England and along the eastern side of the Appalachians.
Ten or fifteen miles north of Morambala, stands the dome-shaped mountain Makanga, or Chi-kanda; several others with granitic-looking peaks stretch away to the north, and form the eastern boundary of the valley; another range, but of metamorphic rocks, commencing opposite Senna, bounds the valley on the west.
Independently of this local metamorphic action, all the strata undoubtedly display an indurated and altered character; and all the rocks of this range the lavas, the alternating sediments, the intrusive granite and porphyries, and the underlying clay- slate are intersected by metalliferous veins.
Looking to the basal, metamorphic, and plutonic rocks of the continent, the areas formed of them are likewise vast; and their planes of cleavage and foliation strike over surprisingly great spaces in uniform directions.
In the present work, therefore, the four great classes of rocks, the aqueous, Plutonic, volcanic, and metamorphic, will form four parallel, or nearly parallel, columns in one chronological table. They will be considered as four sets of monuments relating to four contemporaneous, or nearly contemporaneous, series of events.
As all the crystalline rocks may, in some respects, be viewed as belonging to one great family, whether they be stratified or unstratified, metamorphic or Plutonic, it will often be convenient to speak of them by one common name.
Aqueous, Plutonic, volcanic, and metamorphic Rocks considered chronologically. Terms Primary, Secondary, and Tertiary; Palaeozoic, Mesozoic, and Cainozoic explained. On the different Ages of the aqueous Rocks. Three principal Tests of relative Age: Superposition, Mineral Character, and Fossils. Change of Mineral Character and Fossils in the same continuous Formation.
For it is scarcely possible that such rocks could have been solidified and crystallised while uncovered; but if the metamorphic action occurred at profound depths of the ocean, the former protecting mantle of rock may not have been very thick.
Darwin are strictly to the point as regards all ordinary developmental and metamorphic changes, and even as regards transmitted acquired actions, and tricks acquired before the time when the offspring has issued from the body of the parent, or on an average of many generations does so; but it cannot for a moment be supposed that the offspring knows by inheritance anything about what happens to the parent subsequently to the offspring's being born.
The internal impulse is conservative, and tends to the preservation of specific, or individual, form; the external impulse is metamorphic, and tends to the modification of specific, or individual, form.
Word Of The Day