The correlation of bentonite beds which are found in the Echinospherites and Nidulites members of the Chambersburg limestone, between Chambersburg, Pennsylvania, and Martinsburg, West Virginia, is the result of field work done in 1932 and 1933. The authors worked the sections individually,1 and then jointly studied the area in order to check the results obtained.
It is believed that four beds of bentonite in this district can be correlated over a distance of approximately 36 miles along the strike. The sections studied are as follows (Fig. 1): (1) one mile north of Marion, Pennsylvania; (2) two miles southwest of Marion, Pennsylvania;2 (3) Wilson, Maryland; (4) Pinesburg Station, Maryland; (5) Falling Waters, West Virginia; (6) Bedington, West Virginia; (7) quarry of the North American Cement Corporation, three miles north of Martinsburg, West Virginia; (8) near bridge over Opequon Creek, half a mile south of Blairton, West Virginia; and (9) . . .