THE MESOZOIC ERA 



CHAPTER XXII 

 THE TRIASSIC PERIOD 



FORMATIONS AND PHYSICAL HISTORY 



When the sea was excluded from the area between the growing 

 Appalachians and the Great Plains at the close of the Paleozoic, 

 Appalachia appears to have suffered deformation, one result of 

 which was the development of elongate troughs upon its surface, 

 roughly "parallel to the present coast. These troughs became the 

 sites of deposition, and the sediments laid down in them constitute 

 the only representative of the Triassic system in the eastern part of 

 the continent. The open sea seems to have been excluded from the 

 western interior by the beginning of the Triassic period, though sedi- 

 mentation was in progress over considerable areas between the 

 meridians of 100 and 113. Some of these areas appear to have 

 been sites of salt seas and some of fresh lakes, while still others were 

 probably without standing water. Between the meridians named, 

 many areas of relatively high land probably interrupted the con- 

 tinuity of the areas of sedimentation. On the western coast, the 

 ocean began to gain on the continent about the close of the Paleozoic, 

 and the shore of the Pacific was presently shifted eastward to the 

 vicinity of the nyth meridian in the latitude of Nevada. 



In keeping with these changes in geography, Triassic strata are 

 known in three regions: (i) The Atlantic slope east of the Appala- 

 chians; (2) the western interior; and (3) the Pacific coast. The 

 strata in these three regions are in many ways unlike. 



The Eastern Triassic 



Distribution. The Triassic system of the east occurs in spots 

 from Nova Scotia to South Carolina, as shown in Fig. 412. Its- 

 several areas are mostly elongate in a northeast-southwest direction. 

 The beds of these several areas have been grouped under the name 



Newark (Newark, N. J.). 



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