Igneous Rock: Subjected to these agonies of birtl% and being, the earth has written its autobiography in letters of stone, and rocks are the documents of earth history, for all to read who can.
The Three Classes of Rock.—Geologists recognize three classes of rocks which together compose the lithosphere: igneous, sedimentary, and metamorphic rocks. Igneous rocks have crystallized from a partly or wholly liquid melt of rock matter called magma.
Metamorphic recrystallization may be A thorough and accompanied by marked change chemical compositions, especially if it takes p at depths where high temperatures and pressi prevail. The distinction between igneous metamorphic rocks then becomes vague. Not naturally there are many geological controver concerning the origin and mode of formatior these mixed igneous-metamorphic rocks, or r matites. Granite was formerly regarded a typical igneous rock, but it is now thought some granites may have crystallized from n mas, while others may have been formed by thorough recrystallization of pre-existing ro Distribution of Rocks.See Also Mass Of Rock Around:A rock is not a homogeneous mass of rock around of mate¬rial with a constant chemical composition throughout its bulk. If a rock is examined closely it is seen to be made of many compo¬nents, each quite different from the others and usually forming discrete crystals. These individual components are the minerals.
The movement of the earth's crust may carry the rock as much as 700km (454 miles) below the surface. Here the temperature and pressure will be even higher and the rock will begin to melt. Molten rock is lighter than solid rock and it will begin to rise up through the overlying rock towards the surface. If it reaches the surface as a lava flow it will immediately be ready for weathering and erosion and the start of a new cycle. More often the molten rock solidifies underground and then all the rock above it must be eroded away before it can begin the cycle again.
On The Other Hand See Steep Rock Pinnacle:Special wonders and curiosities of France leap to our thought. Mont-Saint-Michel; Falaise, with the castle where William the Conqueror was born; Le Puy, with its shrine on top of an incredibly steep rock pinnacle; Les Baux, the lofty Christmas village of the south; Rocamadour, in its rock-bound ravine, where Zacchaeus is supposed to have holed up as ""Saint Amadour"; Vezelay, of the Magdalene; Sainte-Odile, hilltop con¬vent of the Alsatian patroness; the photogenic Pont-du-Gard; Aigues-Mortes, port of the Crusaders; Les Saintes-Maries-de-la-Mer, the now land¬locked "Port of the Three Marys"; the Rock of Monaco (but see under Monaco chapter) and La Turbie, high above it, with a view clear to Corsica. All these are scarcely more than random names picked out of the hat.
Special wonders and curiosities of France leap to our thought. Mont-Saint-Michel; Falaise, with the castle where William the Conqueror was born; Le Puy, with its shrine on top of an incredibly steep rock pinnacle; Les Baux, the lofty Christmas village of the south; Rocamadour, in its rock-bound ravine, where Zacchaeus is supposed to have holed up as ""Saint Amadour"; Vezelay, of the Magdalene; Sainte-Odile, hilltop con¬vent of the Alsatian patroness; the photogenic Pont-du-Gard; Aigues-Mortes, port of the Crusaders; Les Saintes-Maries-de-la-Mer, the now land¬locked "Port of the Three Marys"; the Rock of Monaco (but see under Monaco chapter) and La Turbie, high above it, with a view clear to Corsica. All these are scarcely more than random names picked out of the hat.
|
