Rich deposits of clay fed the brickmaking industry of Philadelphia and the surrounding region. In this map, dated 1905, green and tan shaded areas indicate clay deposits in New Jersey, where wide-ranging deposits of clay run diagonally across much of the state. Arguably, the best quality was found in Middlesex County, however suitable clay could also be found across the southern portion, particularly along the Delaware River in Burlington County. In Philadelphia, the best quality brick clay was in the “Neck,” between the Delaware and Schuylkill Rivers.
Map from The Clays and Clay Industry of New Jersey, by Heinrich Ries and Henry B. Kümmel (MacCrellish and Quigley, 1904).