In Secs. 34 and 35, T. 4 S., R. 4 E., Marshall County, Oklahoma, about 7 miles northwest of Madill, there is a group of outcrops of pre-Pennsylvanian rocks (Fig. 1), which have not heretofore been described in print. They occur 3 or 4 miles south of the northern limit of the Gulf coastal plain, as marked by the north edge of the Trinity sand. Being difficult of access, they were easily overlooked in the mapping of the Tishomingo quadrangle 25 years ago.
The accompanying detail map (Fig. 2) shows the exact distribution of these exposures,...
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