Radiolarites.—The writer has had occasion to study deposits of radiolarites in different parts of the world. He observed them along the south border of the Alps in the “zone du Canavese,”3 in the Dutch East Indies on the Island of Boeroe, one of the Moluccan Islands,4 and in California where they are found in the Franciscan formation.

Radiolarites, sometimes called phtanites, consist of a chert containing radiolaria. The glossary, published by the United States Bureau of Mines, gives the following definition of “chert.”5

Chert. A compact, siliceous rock formed of chalcedonic or opaline silica, one or...

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