It is shown that Upper Cambrian rocks are more extensive on the south shore of Port au Port Peninsula than was known, and that they interrupt the supposedly continuous type section of the Lower Ordovician St. George Formation. Trilobites and graptolites in the Humber Arm Group show that its age ranges from LateCambrian through Canadian. Boulders from limestone conglomerate bands in the group have yielded Franconian (Upper Cambrian) and Whiterock (early Middle Ordovician) trilobites; these conglomerates are like those in the Cow Head Group. Thus, part of the Humber Arm Group was deposited during the same time interval as part of the Cow Head Group. The Humber Arm rocks, however, include a greater thickness of sandstone and shale than do the rocks of the Cow Head Group.