Throughout much of the Rocky Mountains and Great Plains region of the western United States there are extensive deposits of red sediments (so-called "Red Beds"), containing layers of salt and gypsum, from 200 to 1,000 or more feet thick. These strata commonly rest in regular order on Permian Red Beds, so that conditions of deposition of Permian time continued through Triassic time, that is continental deposits formed mostly in salt lakes, fresh lakes, along stream courses, and on land in part by the action of wind. [Illustration: Fig. 40.--Map showing the general relations of land and water in North America during the Triassic period. Lined areas represent land; vertical-lined areas, basins in which continental deposits formed. (Based upon map by Willis; courtesy of the Journal of Geology.)] In the eastern half of North America there is no record of accumulation of any marine strata whatever, because, as a result of the Appalachian Revolution, the land was brought well above sea level. There was, however, deposition of a remarkable series of nonmarine strata in several long, narrow, troughlike depressions whose trend was parallel to, and just east of, the main axis of the newly formed Appalachian Range. These troughs lay between the Appalachians and the very persistent old land mass called Appalachia which we have already described. The facts that these troughs are truly down-warps; that they so perfectly follow the trend of the Appalachian Mountain folds; and that the strata in them are of late Triassic Age, make it certain that they were formed by a great lateral pressure which must have been a continuation of the Appalachian Revolution. Thus the Appalachian Mountains continued to grow well into the Triassic period, and, while the Paleozoic strata were being folded, the surface of old Appalachia (including part of the Taconic Mountain region) was down-warped to form the troughs in which the late Triassic strata accumulated. One trough extended through the Connecticut Valley; another (the largest) from southeastern New York through northern New Jersey, southeastern Pennsylvania, Maryland, and into Virginia; while several smaller ones occurred in Virginia and North Carolina.