Measurements of remanent magnetization were made on cores prepared from 54 samples collected from a 50 mi2 area of the St. Francois Mountains, Missouri. The rocks studied are devitrified Precambrian volcanics. In some of these rocks, the stable magnetization has high coercivity and appears to reside in fine-grained magnetite that was formed by devitrification and vapor-phase crystallization. This magnetization is inferred to be chemical remanent magnetization. The remanent magnetization directions from all the samples are closely grouped after demagnetization in ac fields of 500 to 800 oersteds. The calculated mean direction is coincident with the mean directions of other Precambrian igneous rocks of the St. Francois Mountains. The calculated pole position is 141.0°W, 0.9°S.
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Hsu et al. (1966) studied this question.
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