GEOLOGY. 



THE MESOZOIC ERA. 

 CHAPTER XII. 



THE TRIASSIC PERIOD. 



The crustal movements which affected the North American con- 

 tinent during the closing period of the Paleozoic era, and the accom- 

 panying 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 rela- 

 tively 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 reg'on, though there were still considerable areas 

 of sedimentation between the meridians of 100° and 113°. Some 



