Current orthodoxy claims that more than 600 million years ago, ocean-floor spreading had produced an ocean called Iapetus a couple of thousand kilometers wide, roughly but not exactly on the site of the present North Atlantic Ocean, which separated North America and Africa-Europe, much as the North Atlantic does today. This ocean was filled with sandstone, shale, and limestone during the early Paleozoic (609 to 400 million years ago), but during the Middle Devonian (some 370 million years ago), earlier ocean-floor spreading was replaced by subduction, which dragged the ocean floor down into the mantle, bringing northern Africa and Europe back against North America, and squeezing up the sediments to form the Caledonian fold mountains of Scandinavia, Scotland, and Ireland, and the Appalachian Mountains of eastern North America, which completely obliterated the Iapetus Ocean. It was not until the Rhaetic Epoch, about 200 million years ago, that a long chain of rift valleys, which rapidly filled with coarse sediments and basaltic lava, initiated the opening of the modern Atlantic Ocean. The axis of this new rifting had rotated some 30 degrees counterclockwise from the early Paleozoic trend, so most of the early fold mountains were on the eastern side of the new ocean in Britain and Scandinavia and most of them on the western side in North America, although residuals of the Appalachians were left in northwestern Africa and parts of the Caledonides on the east coast of Greenland.
No one disputes that the Caledonian and Appalachian fold mountains in Scandinavia, the British Isles, Greenland, northwestern Africa, and eastern North America were a single mountain system that was folded during the Devonian (also at some other times), and fragmented and separated during the Mesozoic opening of the North Atlantic. But what I do deny is that the Iapetus Ocean ever existed. The primary reason for postulating Iapetus was the orthodox assumption that fold mountains result from subduction of earlier ocean floor. Hence in this view a significant seaway had to be postulated there before the subduction. Moreover, this appeared to be strongly confirmed by the fossil faunas and paleontography. Whereas clear evidence of Ordovician continental glaciation was found throughout the northwestern bulge of Africa, limestones with subtropical faunas were traced along the western slopes of the Appalachians, apparently much too close to the frigid ice sheets unless there was wide separation between Africa and North America at that time. The Ordovician trilobite faunas on the west side of the axial zone of the Appalachians and Caledonides were also incompatible with those adjacent to them on the east side. Trilobite genera occupying similar ecological environments were so different genetically that it seemed impossible that they could have lived so close together for so many millions of years. They needed to have been separated by a barrier such as a wide ocean a thousand kilometers or more wide.
Certainly these trilobite faunas could not have been so near each other as they are now found. But the separation was 3000 km along the axial line of the Appalachians and Caledonides, not across it. Restoring this separation brings the trilobites of Pennsylvania back to face those of Scandinavia, with which they are compatible. I first recognized this gross shear along the axial zone of the Appalachians from the S-shaped distortion of the ''Granville front,'' the boundary of the Late Proterozoic fold-mountains that preceded the 1 Appalachians (Fig. 38). Later, firm confirmation came from paleomagnetic measurements.
During the early Paleozoic time interval when the Iapetus Ocean is alleged to have existed, lavas and other suitable rocks were magnetized by the contemporary magnetic held, so that these rocks recorded their latitude and the direction to the pole. Such rocks, irrespective of whether they were in North America, Africa, or Europe, would indicate the same position for the pole. But if during the Devonian Period the hypothetical Iapetus Ocean was closed by the subduction of its floor, and the Africa-Europe plates collided with the North America plate, the pole indicated by Africa and Europe would come to differ from the pole indicated by the America plate by the amount of the closure and in the direction of the closure.
Dr. W. A. Morris pioneered the investigation of this question, and found that indeed the poles had separated by some 30 degrees, but the separation was in the direction of the Appalachian-caledonian axis, and not transverse to it as it would have to be if the alleged lapetus Ocean had been subducted. Throughout the Early Paleozoic Era up to and including the Early Devonian (about 370 million years ago), southern Britain lay adjacent to North Carolina (Fig. 39). The Ordovician trilobite fauna of Pennsylvania was adjacent to the Baltic faunas. During the Middle Devonian (a time when the Appalachian and Caledonian belts were strongly folded), Africa and Europe were sheared 30 degrees counterclockwise, bringing northwestern Africa opposite North Carolina. Morris's conclusions have since been confirmed by other paleomagneticians with some variations in detail; for example, some think that the shearing displacement continued for 50 million years into the Carboniferous. This is quite acceptable, because both the Caledonian shearing torsion and the later Tethyan torsion movements probably lasted something like 100 million years. Caution is necessary with paleomagnetic data because some rocks have been demagnetized several times, making it essential that the geologic date of each separate magnetization be identified.
The alleged anomaly between the northwest African glaciation and the subtropical limestones of the western slopes of the Appalachians during the Ordovician is also eased by the displacement along the Appalachian axis, but on an expanding Earth, it was not anomalous anyway. If the pole be assumed to have been in the center of the records of glaciation and the earth's radius assumed to have been 0.7 of the present radius, the most northerly glaciate in northwest Africa would have been in latitude 43° (the same as the most northerly Quaternary glaciate at sea level in Tasmania), and the subtropical Ordovician limestones would have been in the latitude of the present Great Barrier Reef of Queensland. The evidence for Iapetus, and the mythical ocean itself, vanish.
