If you would like to learn more about rocks and minerals in general, the names of several reference books are listed on [page 100]. In addition, scientific reports that describe in detail many of the rocks and minerals of Texas have been published by the Bureau of Economic Geology of The University of Texas, the United States Geological Survey, and other organizations. A selected list of these reports is given on pages [100]-101.
Rocks and minerals are familiar objects to all of us. We pick up attractive or unusual [pebbles] for our collections, we admire rocky mountain peaks, we speak of the mineral resources of our State and Nation. Rocks and minerals enter, either directly or indirectly, into our daily living. From them come the soils in which grow the grains, the fruits, and the vegetables for our food, the trees for our lumber, and the flowers for our pleasure. The iron, copper, lead, [gold], silver, and manganese, the [sulfur] and [salt], the clays and building stones, and the other metals and nonmetals that we require for our way of living were once a part of the earth’s crust.
Texas’ highest mountain is Guadalupe Peak, right, with an elevation of 8,751 feet. El Capitan, left, has an elevation of 8,078 feet. These peaks in the Guadalupe Mountains in Culberson County consist largely of Capitan reef [limestone], which formed during the [Permian] [Period].
Earth’s Outer Crust
Rocks and minerals make up most of the outer layer or crust of our earth—the actual ground beneath our feet. The crust is approximately 18 to 30 miles thick beneath the continents. In general, the outermost part consists of many layers of stratified rocks, one above another. The older rocks normally make up the bottom or the deeper layers, and the younger rocks form the upper layers. Not all the layers are perfectly flat and parallel—some are lenticular (lens-shaped), some are tilted, some are partly eroded away, and some are present in one place and absent in another. Beneath the continents, the layers of rock rest on ancient [metamorphic rocks] and on great masses of [igneous] rock such as [granite]. These lower rocks are known as the basement.
Earth’s outer crust (thickness not drawn to scale).
Over much of the land surface of the earth, the outermost layer is made up of layers of rock
On the continents, the layers of rock rest on [metamorphic rocks] and on [igneous] rocks such as [granite]