Sedimentary rocks account for about five percent of the earth's outer sixteen kilometers. This layer is important because it holds the clues to earth's past. The layers contain evidence about transport processes, surface environments, and past life. They also are important for the economy. The layers provide energy resources like oil and gas. |
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Sediments are carried by wind, water, gravity, and glaciers. After deposition, the sediments are compacted and cemented together. They are classified into two major categories: detrital and chemical sedimentary rocks. Detrital sedimentary rocks are derived from weathering and include conglomerates, breccias, sandstones, siltstones, and shales. Chemical sedimentary rocks are derived from material carried in solution and can include coal, limestone, travertine. |
Sedimentary rocks form strata or beds which are layers upon layers of accumulated sediments. |
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There are many examples of sedimentary rocks in the Texas Hill Country. Locations such as Marble Falls, Texas and Lost Maples State Natural Area are two great places where sedimentary rocks are highly visible.
Longhorn Caverns is a great place to locate limestone beds that have formed by the downward percolation of rainwater. |
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Dripping water mixes with the cave air to form calcium carbonate. The calcium carbonate continues dripping and forms many unique cave features such as stalactites, stalagmites, draperies, and columns. |
Stalactites hang from the ceiling and stalagmites form right below them. When they meet, they form columns. |
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Inverted potholes were formed by the swirling action of water when there were underground streams. |