As soil develops, it forms layers, or horizons, which are often categorized as: a. a, b, c
b. source, mantle, crust
c. 1, 2, 3
d. dirt, humus, rock

Gemstones are commonly found in pegmatites, which are igneous rocks that are a. exceptionally mafic b. exceptionally coarse grained c. exceptionally fine grained d. extrusive, forming from lava

The meseta in spain is a a. navigable river b. castle c. coastal plain d. plateau

Many areas surrounding the caspian sea contain important a. rare minerals b. forestry resources c. gold and silver mines d. oil and natural gas fields