THE MESOZOIC EEA 



CHAPTER XXIII 

 THE TRIASSIC PERIOD 



FORMATIONS AND PHYSICAL HISTORY 



During the closing stages of the Paleozoic, when the sea was 

 excluded from the area between the growing Appalachians and 

 the Great Plains, Appalachia appears to have suffered deformation. 

 One result of this deformation 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 completely excluded from the western interior by the 

 beginning of the Triassic period, though sedimentation was in 

 progress over considerable areas between the meridians of 100 

 and 113. Some of these areas appear to have been the 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 continuity 

 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 

 117th meridian in the latitude of Nevada. 



In keeping with these changes in geography, Triassic strata- arc 

 known in three regions: (1) 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 The Newark Series 

 Distribution. The Triassic system of the east occurs in spots 

 from Nova Scotia to South Carolina, as shown in Fig. 464. Its 



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