| Reference | {Deposit:: F1 < BROWN, C.E., 1966, PHOSPHATE DEPOSITS IN THE BASAL BEDS OF THE MAQUOQUETA SHALE NEAR DUBUQUE, IOWA, IN GEOLOGICAL SURVEY RESEARCH 1966: U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 550-B, P. B152-B158.}{Deposit:: F2 < BROWN, C. E., 1974, PHOSPHATIC ZONE IN THE LOWER PART OF THE MAQUOKETA SHALE IN NORTHEAST IOWA: U.S. GEOLOGICAL SURVEY JOURNAL OF RESEARCH, V. 2, NO. 2, P. 219-232.} |