This component of the tapestry is simplified from
the geologic map of King and Beikman (1974). Rocks contain
information essential to an intelligent understanding of the Earth
and its long natural history. Geologists determine the location,
geographic extent, ages and physical and chemical characteristics
of rocks and unconsolidated (loose) materials. To express these
attributes geologists have developed a unique method of portrayal,
the geologic map, which has the following properties:
- It recognizes similarities and differences among materials
that make up the Earth's crust and classifies them by type of
rock or surficial deposit;
- It ascribes Earth materials to a specific environment or mode of origin- for example, volcano, river deposit, windblown dune, limestone reef, alteration at depth by heat or pressure;
- It identifies rock formations of distinctive materials and ages that are the three-dimensional building blocks of the Earth's crust; it further shows the relative position of one formation to another at the Earth's surface;
- It arranges rock formations of different ages into a time sequence from which the geologic history of the planet can be deciphered.
Reference:
King, P.B., and Beikman, H.M., compilers, 1974,
Geologic map of the United States (exclusive of Alaska and Hawaii):
Reston, Va., U.S. Geological Survey,
three sheets, scale 1:2,500,000.
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