Abstracts Earth and Environmental Sciences

Stratigraphy and correlation of Precambrian volcanic rocks, Eminence, Missouri

by Henry Hugh Fisher

"A portion of the Precambrian rocks located in the vicinity of Eminence, Missouri are studied and describes. These rocks are exposed as rhyolitic knobs protruding through hills of Ordovician sediments. The Precambrian rocks under study consist principally of rhyolite, with smaller amounts of tuff and creccis. The rhyolite is a potash rhyolite porphyry, both flow banded and unbanded, with phenocrysts of kaolinized orthoclase in a matrix of quartz and orthoclase. The tuffs contain devitrified glass shards and occasional ash balls such as those exhibited at Cott Mountain. A stratigraphic sequence was determined with the oldest rocks to the south at Stiegel Mountain and the younger rocks at Coot Mountain to the north. The tuffs occur between rhyolite flows. The entire sequence has a general dip to the north; but local variations in dip and strike occur. Basal conglomerate formed from rhyolite boulders occurs with the Ordovician sediments, particularly at the Little Rocky Creek Ford knob. The possibility that the Eminence rhyolites are ignimbrites was studied and rejected" – Abstract, Page ii.