In the late Paleozoic, the margin of the North American Plate probably was located well oceanward of the old continental margin. The continents were clustered in the supercontinent called Pangea, while the ancestor of the Pacific Ocean (sometimes called Panthalassa) occupied half the Earth's surface.

The continuity and patterns of sedimentation of the rocks deposited along the old continental margin were unaffected by any mayhem that may have taken place in the terranes. This suggests the two regions were widely separated. There was a second episode of rifting and separation, which started about 360 million years ago and initiated a basin floored by oceanic crust that today is represented by Slide Mountain terrane in the Omineca Belt. West of this, Paleozoic arc rocks occur in Quesnel, Stikine and Wrangellia terranes. Separating Quesnellia from Stikinia, and Stikinia from Wrangellia, are respectively, the Cache Creek and Bridge River terranes which represent remains of former ocean basins.

One of the first pieces of evidence of large scale movement of terranes comes from the differences between Permian fossils (280-260 million years ago) in shallow water limestones within these terranes. Fossils found on the continental margin are the remains of animals that appear to have lived and died at latitudes mid-way between the Permian equator, the located at the latitude of Texas, and the cooler waters of the present Canadian Arctic. Fossils in Slide Mountain, Quesnel and Stikine terranes most closely resemble forms that lived on the old continental edge in the southwestern United States. Remarkably, Permian fossils in the Cache Creek terrane resemble those in Japan, China, and southeast Asia, which perhaps is not surprising as they occur in a subduction complex that represents the remains of a large ocean. Those in Wrangellia resemble cooler water faunas, today found in the Canadian Arctic or the Russian Urals, although some fossils are similar to those in Timor (which itself was probably in an unknown location). This scrambling together in the Cordillera of the remains of animals that probably lived, died and were buried at different latitudes and in different parts of the world is explained by later plate movements which carried the rocks in which they are buried into the positions they presently occupy along the old continental margin.