NO. 23.] CENTRAL CONNECTICUT IN THE GEOLOGIC PAST. 21 



mostly red or brown shales and sandstones with, in certain local- 

 ities, many conglomerate beds. Intrusions of tra.p were forced 

 into these sediments as molten sheets, and at three separate times 

 great floods of lava spread far and wide over the surface. These 

 were poured out while the Triassic muds and sands were accumu- 

 lating and subsiding, and each in turn became buried beneath 

 the later beds of the formation. Uplift of the neighboring 

 regions and subsidence over the region of accumulation permitted 

 erosion and sedimentation to proceed until a maximum thickness 

 of certainly more than two miles, very possibly as much as three 

 miles, had accumulated. The sediments and the lavas were laid 

 down in approximately horizontal sheets, but they now exhibit 

 a regional dip to the east which averages from fifteen to twenty 

 degrees. Erosion has planed across these inclined strata, ex- 

 posing them to view from top to bottom. The trap flows consist 

 of harder rock and have not been worn so low as the soft rocks 

 which underlie the valley floor. The outcrops of the lavas, how- 

 ever, are broken and offset and repeated, indicating that the 

 Triassic formation has been shattered into great crust blocks 

 which have slipped on fault planes hundreds or even thousands 

 of feet with respect to each other. The original position of the 

 sediments has therefore been modified by both tilting and fault- 

 ing as shown on the structure section. The floor upon which the 

 Triassic land waste began to be laid down has again become 

 exposed as the eastern slope of the Western Highland. It is a 

 fairly plane surface eroded across various metamorphic rocks, 

 and indicates a great lapse of time following the elevation of the 

 late Paleozoic mountains, before the beginning of the Triassic 

 sedimentation. 



The life record as shown by the abundant footprints and the 

 rare fossil bones belongs to the upper Triassic and may extend 

 into the Jurassic period. 



Later than the Triassic the only deposits in Connecticut con- 

 sist of the thin mantle of Glacial drift, and surface gravel, sand, 

 and clay, which marks the presence and the retreat of the conti- 

 nental ice sheet of the geologically recent Quaternary period, 

 the age of ice. After this general review of the geology of central 

 Connecticut, attention may be turned to the structure sections 



