Abstract
Restudy of graptolite assemblages from the classic Castle Brook locality near Magog reveals that 2 graptolite zones, those of Climacograptus bicornis and Orthograptus truncatus var. intermedius, are present there. These zones indicate a late Middle Ordovician (Wilderness and Trenton) age for the rocks comprising them. If the graptolite-bearing slates are included in the Beauceville Group, the lower part of that unit is, therefore, Wilderness and Trenton in age. The graptolite-bearing rocks near Magog and the Normanskill Formation may be correlated because the same 2 graptolite zones are present in both units. The Magog graptolite-bearing strata are thus not younger than the Normanskill Formation, as has long been thought, and the graptolite fauna of the Magog rocks does not belong in a zone distinct from those in the Normanskill Formation.
