452 



MESOZOIC ERA— AGE OF REPTILES, 



Life-System. 



The characterization of the life-system of the Jura-Trias period 

 in America is best brought out in connection with a description of 

 some of the more interesting localities and of their remarkable records. 



Connecticut River Valley Sandstone. — The Strata. — This locality has 

 been made classic ground for the geologist by the indefatigable labors 

 of the late President Hitchcock, of Amherst. The strata border the 



Fig. 712.— General Section across Connecticut River Sandstone (after Davis) : The black, trap. 



Connecticut River, on both sides, through the whole of Massachusetts 

 and Connecticut, as far as Middletown, where the river trends to the 

 east while the sandstone area passes straight on to the sound at New 

 Haven. The whole forms an irregular area about 110 miles long and 

 20 miles wide. They consist of red sandstones and shales, dipping some- 

 what regularly to the east, at an angle of about 20° to 30°,. indicating a 

 thickness of at least 5,000 feet (Dana) to 10,000 feet (Hitchcock). The 

 general relations of the strata with the intrusive trap and the under- 

 lying gneiss are shown in the accompanying figures (712 and 713). 

 The trap is seen to be conformable with the strata, but the whole series 

 has been subsequently fissured and faulted in such wise that the strata 

 are repeated and the thickness is apt to be overestimated, as already 

 explained on page 230. The trap-ridges are formed by the outcrop of 

 the tilted and faulted sheets of lava. This regular dipping to the east 

 throughout the whole series can be most easily explained by supposing 

 that at the end of the Jurassic the whole area of previously-horizontal 

 strata (Fig. 712, A) was lifted into an incline of 20° or more, and after- 

 ward cut away by denudation, as shown in the diagram (Fig. 713, B). 

 In the elevation the strata were fissured and faulted, as shown in 

 Fig. 712. 



A a 



The whole series of sandstone is very distinctly stratified, and in 

 many parts beautifully fissile. When these parts are broken open 

 along their lines of lamination, all kinds of shore-marks are found in 



