Triassic SystemThis system has but limited representation in the eastern part of the United States, being known only east of the Appalachian Mountains in an area which was land throughout most of the Palaeozoic era, hut which was deformed when the eastern mountains were developed at the close of the Palaeozoic. In the troughs formed in its surface during this time of deformation, sediments of great thickness accumulated during the Triassic period.
To this strength the geographic isolation enforced by the Appalachian mountains had been a prime contributor.
In many places, but in and near the Appalachian Mountains its thickness is much greatermore than five times as great if the maximum thicknesses of all formations be made the basis of calculation.
Thus there is here a gap, easily traversed, across the Appalachian mountains and plateaus to the more level and fertile plains beyond.
Lay east of the site of the Appalachian Mountains throughout the Palaeozoic era, and quantities of sediment from it Were accumulated where these mountains were to arise later.
Similar events were meanwhile happening in North America, for the seas were steadily filled with sediments which drove them from the northeast towards the south-west, and doubtless those movements which at the close of this period uplifted the Appalachian mountains were already operative in the same direction.
West of where the escarpment dies out, the Great Valley Region and a considerable portion of the Appalachian Mountains Region are drained by the Coosa, the Tallapoosa and their tributaries, into Mobile Bay, but the Cumberland Plateau, like that part of the Appalachian Mountains Region which lies directly N.
In eastern New York, and almost as much in the southern Appalachian Mountains (Georgia and Alabama); but its average thickness is much less.
During exercises, the government's premier contingency operations compound in the Appalachian Mountains of Tennessee was populated only by maintenance crews and a few relaxed guards.