GLOSSARY OF GEOLOGIC TERMS. 201 
Meander. To flow in serpentine curves. A loop in a stream. The term comes 
from the Greek name of a river in Asia Minor, which has a sinuous course. Most 
streams in flowing across plains develop meanders. (See Pl. III, A, p. 11.) 
Metamorphism. Any change in rocks effected in the earth by heat, pressure, 
solutions, or gases. A common cause of the metamorphism of rocks is the intru- 
sion into them of igneous rocks. Rocks that have been so changed are termed 
metamorphic. 
Monzonite. An even-grained intrusive igneous rock intermediate in character 
— go and granite. It resembles granite. 
Moraine. A mass of drift deposited by a glacier at its end or along its sides, 
Oil ours An canis or body of oil in sedimentary rock that yields petro- 
leum on drilling. The oil occurs in the pores of the rock and is not a pool or 
pond in the ordinary sense of these words. 
Outcrop. That part of a rock that appears 2 the surface. The appearance of a 
rock at the surface or its projection above the soil. 
Paleontology. The study of the world’s iat life, either plant or animal, by 
means of fossils. 
Peneplain. A region reduced almost toa plain by the long-continued normal ero- 
sion of aland surface. It should be distinguished from a plain produced by the 
attack of waves along a coast or the built-up flood plain of a river. 
Petrography. The description of rocks, especially of igneous and metamorphic 
rocks, studied with the aid of the microscope. 
Petrology. The study of rocks, especially of igneous and metamorphic rocks. 
Placer deposit. A mass of gravel, sand, or similar material resulting from the 
crumbling and erosion of solid rocks and containing particles or nuggets of gold, 
platinum, tin, or aye valuable minerals, which have been derived from roc 
eins by e 
Playa (pounced playa). The shallow central basin of a desert plain, in which 
water gathers after a rain and is evapora 
Porphyry. rie ny igneous rock in which certain crystal constituents are distinctly 
visible in contrast with the — substance of the roc 
Quartzite. A rock composed of sand grains cemented by silica fete an extremely 
hard mass 
—— a lava, usually of light color, corresponding in chemical composition to 
granite. The same molten liquid that at great depth within the earth solidifies 
as granite would, if it flowed out on the surface, cool more quickly and erystal- 
lize less completely as rhyolite. 
Schist. A rock that by subjection to heat and pressure srisbaias the earth has under. 
gone a change in the character of the particles or minerals that compose it ‘ind 
has these minerals arranged in such a way that the rock splits more easily in 
certain directions than in others. A schist has a crystalline grain roughly com- 
parable with the grain of a piece of wood. 
Sedimentary rocks. Rocks formed by the accumulation of. sediment in water 
- the remains or products of animals or plants pores limestones and coal); of the 
isan materials. Some its ( 
blown from volcanoes and PR on wien or in wate. A @haractoristic fea- 
ture of sedimentary deposits is a layered structure known as bedding or strati- 
fication, Each layer is a bed or stratum. Sedimentary beds as deposited lie 
flat or — flat. 
: Shale. A rock consisting of hardened thin layers of fine mud. 
