No. 23.] CENTRAL CONNECTICUT IN THE GEOLOGIC PAST. 33 



mountain s, but to what extent they were built at the end of the 

 Paleozoic and to what extent in some of its earlier periods is 

 unknown. The fact, however, that the mountains had become 

 removed by the middle of the Triassic period suggests that, . al- 

 though the crtistal forces may have been intense during the last 

 movements of the revolution which closed the Paleozoic, the 

 elevation of the regions of subsequent Triassic sedimentation may 

 not have been great. The regions which were later occupied by 

 Triassic rocks may already by the close of the Paleozoic have 

 formed intermontane depressions premonitory of the subsidence 

 of the Triassic. This conservative interpretation has been 

 adopted in the structure section. On the other hand, the forces 

 of erosion have been found capable of removing mountains within 

 the time limits of a single geologic period. A time of unknown 

 duration extended between the Permian folding and the middle 

 Triassic, a time unrecorded by sediments in eastern North 

 America. It is not an unreasonable supposition therefore that 

 in this time-interval mountains of great volume may have been 

 worn away. Certain it is that in eastern New England vast 

 bodies of granite were intruded into the crust in the great revo- 

 lution which closed the Paleozoic and which is known as the 

 Appalachian Revolution. In northern New Jersey also are in- 

 trusions which can be proved to be later than the * Silurian. 

 Furthermore, much of the metamorphism of western New Eng- 

 land is thought by the writer to belong to the late Paleozoic, 

 since post-Ordovician sediments are everywhere altered. Where 

 such great intrusion, folding, and metamorphism are taking place, 

 a mountainous relief is certain to come into existence; but be- 

 tween the mountain ranges may lie intermontane troughs, and 

 it is possible, although no evidence bears upon this conclusion, 

 that central Connecticut may have been such a trough. 



There is still to be considered the meaning of the granite- 

 gneisses which penetrate the foundation rocks of the region. 

 These welled up as abyssal molten masses magmas laden with 

 steam and other gases. They rose from the depths in successive 

 stages : they forced their walls apart, or broke off and swallowed 

 portions of the adjacent rocks, and raised the superincumbent 

 crust into irregular mountain domes. The evidence still shows 

 that sheets of molten rock penetrated into cracks in the over- 

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