Excerpt from Geology, Vol. 3 of 3
The crustal movements which affected the North American continent during the closing period of the Paleozoic era, and the accompanying changes in geography, have been noted. From the area between the growing Appalachians and the Great Plains the sea was excluded. The surface of Appalachia, lying east of the Appalachian Mountains, and extending eastward perhaps beyond the present coast, the land which throughout the Paleozoic era had furnished sediments to the sinking trough where the Appalachian Mountains were to arise, suffered deformation during the closing stages of the Paleozoic or soon after, and parts of its surface were converted into areas of deposition. These areas were in the form of long and relatively narrow troughs, roughly parallel to the present coast. In them, sediments from the surrounding land were laid down, and constitute the only representative of the Triassic system known in the eastern part of the continent. It is not known that the deformation of the surface of Appalachia brought any part of the present land area beneath the ocean.
In the west, the geographic changes which marked the transition from the Paleozoic were scarcely less important. The more or less open sea of the western interior during the Mississippian and Pennsylvanian periods was largely excluded at the close of the Carboniferous. In the Permian period, it is true, the sea had at least temporary access to an extensive area in the western interior (Vol. II, p. 621); but in the Triassic period the open sea seems to have been completely excluded from this region, though there were still considerable areas of sedimentation between the meridians of 100° and 113°.
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