TY - `BOOK` AU - Ludvigsen, Rolf TI - A trilobite zonation of Middle Ordovician rocks, southwestern District of Mackenzie PB - Geological Survey of Canada CY - Ottawa PY - 1979 LA - eng SE - 98 S. T2 - Bulletin / Geological Survey of Canada M1 - 312 SN - 0-660-10165-3 SN - 978-0-660-10165-1 CN - 79 S 203 AN - UBHD-1475964 ER -