Rock gypsum is mainly used in making “plaster of Paris,” as a retarder in cement, and as a fertilizer (so-called “land plaster”).
[GLOSSARY OF COMMON GEOLOGICAL TERMS]
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NAMES of subkingdoms and important classes of fossil plants and animals, and mineral species, are not included; these being briefly and systematically discussed in chapters [17], [18], [19], and [20], respectively. By using the index the reader can quickly locate the page where any one of these names is discussed. Some definitions in this glossary are taken from U. S. Survey Bulletin No. 613.
Anticline.—A kind of folded structure in which strata have been bent upward or arched.
Archeozoic.—The earliest known era of geologic time.
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, and magnesium.
Base-level.—The lowest level to which a stream can cut (erode) its channel. A whole region may be base-leveled by erosion.