CHAPTER XXI 



FIG. 427. Triassic sediments in Connect- 

 icut with a surface flow and intrusions 

 of lava, as they may be supposed to have 

 existed before faulting. 



THE JURASSIC PERIOD 



Land in eastern North America. Rocks which were made 

 during the Jurassic period are not extensively exposed in the 

 United States, and for the most part they are less well known 

 than those of other periods. In the eastern half of the country 

 no rocks which are surely l of this age have been discovered. 

 From this circumstance it seems probable that the eastern 



part of the continent was 



largely out of water, and 



that the erosion of the 



Appalachian region was 



still in progress. After 



the deposition of the 



Newark sediments during 



the later part of the Tri- 



assic period, the eastern 



border of the continent 



was slightly warped. As 



a result, the Triassic rocks 



are now tilted, to the east 



in New England, and to 



the west in New Jersey and southward. During the same 



disturbance the rocks were broken by many normal faults 



which, in some instances, repeat the interbedded sheets of 



lava (Figs. 427 and 428). 



Temporary inundation of the Northwest. Little is known 

 of the events of Jurassic times in the great interior of the 



1 It has been suggested that some doubtful fresh-water deposits along 

 the Potomac River in Maryland are of Jurassic age, but it is equally prob- 

 able that they are Comanchean (Lower Cretaceous). 



405 



FIG. 428. The same, complicated by 

 several normal faults and eroded to a 

 peneplain. 



