gp:ological history of the region. 517 



trap, known as the main trap sheet, the other members of the series be- 

 ing named according to their position with respect to this dominating 

 member; 1,200 feet of posterior shales and sandstones, including a sec- 

 ond bed of fish-bearing black shales; 150 feet of posterior trap, and at 

 least 3,500 feet of upper sandstones and conglomerates. 



The chapter of deposition was brought to a close by an uplift which 

 ended in giving the formation as a whole a faulted monoclinal structure 

 with generall}'' eastward dip. An unknown breadth of crystalline rocks 

 was also disturbed on the east and west. This deformation was accom- 

 panied and long followed by erosion. It is manifest that no close rela- 

 tion can be expected between the dates of beginning and ending of this 

 chapter of deposition and the dates of beginning and ending of any 

 standard division of geologic time ; hence the term Triassic is employed 

 here rather as a makeshift term, following the usage of earlier pa})ers, a 

 departure from which would cause inconvenience, although the authors 

 sympathize with Professor Russell's motive in introducing the non-com- 

 mittal term Newark as a general name for the red sandstone and trap 

 formation of the eastern United States. 



It is important to recognize that the erosion introduced by the mono- 

 clinal deformation has' completed one cycle of destructional processes 

 and has advanced well into another cycle. The constructional topogra- 

 2)hy introduced at the close of Triassic deposition lias been completely 

 extinguished, the denudation of the first cycle even reaching to effective 

 baselevcling and producing an extended pene})lain of moderate relief 

 over the adjacent crystallines as well as along the Triassic belt. 



Whatever oscillations of level may have occurred during the later 

 stages of denudation of the peneplain, they have not left significant 

 topographic marks ; but after it was developed there was a submergence 

 of its southward margin, by which the sea was allowed to lap over it, 

 and sediments bearing Cretaceous fossils were laid down in these en- 

 croaching waters. The inland extension of the Cretaceous submergence 

 and dei)Osition is not yet determined, although it is hoped that when the 

 structure of the crystalline rocks of Connecticut is better understood the 

 innermost Cretaceous margin may be discovered by means of the rela- 

 tions of revived and superposed streams and rivers. 



At some later stage than the dei)Osition of the Cretaceous cover on the 

 border of the peneplain, and hence presumably within the limits of Terti- 

 ary time, a considerable northward uplift occurred, giving the old lowland 

 an altitude of over a thousand feet in Massachusetts and further north, 

 increasing the slope of the southward rivers and rejuvenating all their 

 fading activities. At the same time at least a part of the submerged area, 

 with the Cretaceous cover on its back, was raised above sealevel, and the 

 rivers were presumably extended across the Cretaceous coastal plain to 



