Recently there has come to the writer’s notice an interesting volcanic ash or tuff from Calcasieu Parish, Louisiana, which because of its distinctive character, may be of interest to other students of subsurface geology of the Gulf Coastal Plain. Volcanic ash and glass have been reported from the later Mesozoic and Tertiary deposits of the Gulf Coastal Plain in numerous papers, but in few of these have any definite data been given concerning petrographic character. These deposits have been referred to as “volcanic glass,” “rhyolitic ash,” etc., but seldom has the index of refraction of the material been given. In...
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