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This rock outcrop is part of Castle Rock, in Kansas. What is so amazing about the rocks?

Answer:

This is the Niobrara Chalk, a layer of rock that runs all the way from Kansas to Canada. In places it is up to 700 feet thick. One truly amazing thing about this rock is that this huge layer of chalk is made up almost entirely of the fossilized bodies of single celled organisms called foraminifera, each much smaller than a grain of sand.

The upper layer is a harder limestone, that resists weathering. As it crumbles at the edges, the softer chalk underneath weathers away.

Buried in this chalk are the fossils of mosasaurs, plesiosaurs, monstrous fish, and giant clams. During my years as a geologist at the Memphis Pink Palace Museum, this was one of my favorite collecting spots for our summer field schools.

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