Cambrian and Ordovician strata crop out in western Newfoundland in a belt 5-30 mi wide and extending from Port au Port Peninsula north to Cape Norman and across the tip of the Great Northern Peninsula. These rocks are of two distinct facies--one autochthonous and the other allochthonous. Basal Lower Cambrian sandstone beds of the autochthonous facies unconformably overlie Precambrian rocks, and are succeeded by dolomite and limestone of Middle Cambrian to Ordovician Whiterockian age. This sequence is about 4,000 ft thick; there are no angular unconformities within it. The allochthonous facies includes the Cow Head Group, 1,000 ft thick and composed predominantly of limestone and limestone conglomerate, and its lateral equivalent, the thicker (5,000± ft) Humber Arm roup, predominantly of clastic rocks but including some volcanic rocks. These two groups range in age from Middle Cambrian to Ordovician Whiterockian. Conglomerate boulders and bedded rocks of the Cow Head Group have yielded more varied faunas and a more complete faunal succession than other rocks. Cambrian faunas from limestone boulders include both Pacific and Atlantic types. Ordovician faunas from both facies are like those of the rest of North America, including Greenland, and of western Ireland, northern Scotland, and Spitsbergen.

Faunal distributions in the Cambrian and particularly in the Ordovician do not appear to require fo+r their explanation that the Atlantic Ocean was "closed" during these periods.