Study of the outcrop areas of igneous intrusions in the Texas, Arkansas, and Georgia portions of the Gulf Coastal Plain furnishes clues which simplify interpretation of igneous rocks found in deep well samples in the Mississippi Embayment. Many of the known centers of later Mesozoic igneous activity, both outcropping and buried, are apparently the sites of ancient volcanoes which furnished to the depositional basins significant amounts of pyroclastic debris now in part preserved in the early and middle Gulf Cretaceous strata. Dikes transect the oldest known sedimentary rocks in the vicinity of the eruptive centers. The oldest igneous rocks of the Coastal Plain may bear a Triassic date; the youngest were emplaced in late Austin or early Taylor time.

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