No. 23.] CENTRAL CONNECTICUT IN THE GEOLOGIC PAST. 2O, 



there the basal beds disappear toward the north and the sediment 

 was received from both east and west. The muds, sands, and 

 gravels were therefore deposited in basins, the sediments becom- 

 ing thicker in some places than in others, the floor of the basins 

 spreading as progressive subsidence gave opportunity for deeper 

 sediments. 



The strata on the east side of the Lowland show many con- 

 glomerate members, indicating a derivation from uplands which 

 lay near-by on the east, though conglomerates are also found near 

 the western border and to some extent in many parts of the de- 

 posits. But the dominant segregation of conglomerates near the 

 eastern margin is even more marked in the beds above the lava 

 flows than in those below, and this greater average coarseness 

 of the upper sediments indicates the intermittent re-growth of 

 mountains whose perennial waste kept supplying material for the 

 deposits of the basin. It is necessary to postulate a boundary 

 consisting of a fault wall in order that renewed movements upon 

 it may maintain such a long continued supply of coarse, yet local 

 waste. Similar conglomerates are found also at all levels in the 

 beds which abut against the western margin of the New Jersey 

 area of Triassic rocks. These areas were therefore basins facing 

 each other and bounded on their outer sides by faults, beyond 

 which rose mountain walls analogous to the Sierras which look 

 east and the Wasatch which look west over the desert plains and 

 island mountains of the Great Basin of the West. The eastern 

 limit of the Connecticut Triassic and the western limit of the New 

 Jersey area are still on or near this ancient boundary, but the sedi- 

 ments of the two originally extended toward each other to a 

 greater or less distance beyond their present limits, and the upper 

 beds of the Connecticut area may have been confluent in places 

 with those of New Jersey. 



It has been assumed until recent years that practically all 

 sediments came to rest beneath permanent bodies of -water, but 

 wider studies of the earth have shown that great depths of sand 

 and mud may be built up in subsiding areas by rivers, as delta and 

 basin deposits. In the Triassic of Connecticut, shrinkage cracks, 

 raindrop impressions, and animal footprints occur abundantly. 

 These marks of subaerial exposure, together with the presence of 

 land fossils and absence of those belonging to salt water, gave rise 



