Silurian Reef at Grafton, Wisconsin

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Interreef deposits consist of thick beds of fine-grained, partly cross-bedded dolostone with abundant oncolites, which are spherical to ellipsoidal particles formed by concentric layers of microbial organisms. Oncolites indicate agitated waters where particles are rolled frequently over the seafloor, and they also indicate shallow depths where sunlight is available for photosynthesis.



© 1997, Milwaukee Public Museum, Inc.