GLOSSARY OF GEOLOGIC TERMS. 
Andesite. A lava of widespread occurre nce, saaally at dark-gray color and inter- 
mediate in chemical composition between rhyolite and basalt. 
Anticline. An arch of bedded or layered rock suggestive in form of an overturned 
canoe. (See fig. 16, p. 86; fig. 25, p. 117; Pl. XIX, B, p. 103.) See also Dome 
and Syncline e.) 
Badlands. A region nearly devoid of vegetation where erosion, instead of carving 
hills and valleys of the familiar type, has cut the land into an intricate maze of 
harrow ravines and sharp crests and pinnacles. Travel across such a region is 
almost impossible, hence the name. (See Pl. XXII, p. 110 
Basalt. A common lava of dark color and of great fluidity when molten. Basalt is 
less siliceous than granite and rhyolite, and contains much more iron, calcium, 
d magnesium. 
Bolson (pronounced bowl-sown’ ). A flat-floored desert valley that drains to a central 
ya. 
Breccia (pronounced bretch’ya). A mass of naturally cemented angular rock frag- 
ding. Irregular bedding at an angle oblique to the general plane of strat- 
ification (see Sedimentary rocks), formed by the action of tides or currents vary- 
ing it in direction and force. (See Pl. A ViE.p. WL: Pl Xxx, p. 119 
Diabase. A heavy, dark intrusive rock having the same ition as basalt but, 
on account of its slower cooling, a more crystalline texture. Its principal con- 
stituent minerals are feldspar, augite, and usually olivine. Olivine is easily 
changed by weathering, and in many diabases is no longer recognizable. Augite 
Diorite. An even-grained € igneous rock consisting chiefly of the minerals 
feldspar, hornblende, and very commonly black mica. If the rock contains 
q , itis quartz diori Quartz diorite resembles granite and is 
Iron, Magnesium, calcium, and other constitue 
Dip. The slope of a rock lever expressed by the ar which the top or bottom of 
the la ith a horizontal plane. ( ages 3, p. 14; fig. 13, p. 71; Pl. 
XVIII, p. srl rt XX, B, p. 106.) (See also Stri ke.) 
»Y erosion into hills and valleys. Applicable especially to plains 
or sen in process of erosion after an uplift. 
are aes applied to rock layers or beds, a ea anticline, suggestive of an inverted 
a 
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