32 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



being necessarily alpine heights at any time. Truly, Triassic 

 time was long as measured by its work. 



Beginning of the Triassic Sedimentation, Figure 8. Remove, 

 in imagination, all but the basal layer of the Triassic sediments, 

 and restore the region to the appearance which it presented 

 before the two, three, or more miles of mud, sand, gravel and lava 

 were poured into the sinking basin. A period of erosion just closed, 

 had reduced the previous generation of mountains in this area to 

 isolated hills, and exposed the basal granites and metamorphic 

 rocks. This ancient land surface is still preserved, as Davis has 

 pointed out, as the floor upon which the sediments began to be 

 laid down, and is re-exposed to view on the eastern slopes of the 

 Western Highland by the erosion of the softer Triassic rocks. 

 The straightness and planeness of this tilted floor, where not 

 broken by later transverse faults, indicate that the land had been 

 worn down to a moderate relief before the sediments began to 

 be deposited, showing hills perhaps not more than some hundreds 

 of feet in height. The structure section shows the beginning of 

 the basin as a tendency to downwarp on the one side and upwarp 

 on the other, with the result that the hills are rejuvenated by 

 the uplift and their waste begins to bury the crystalline floor of 

 the basin. But so long as erosion and deposition are more rapid 

 than subsidence no permanent water body can result, as the sedi- 

 ment is more than sufficient to keep the basin filled. It is assumed 

 in the structure section that a differentiation of the subsiding 

 margin of the basin from the rising rim so sharp as to require 

 the development of a fault zone, had not yet arisen, though such a 

 plane of weakness possibly may have been inherited from some 

 earlier time and may have served as a plane of motion at the 

 very initiation of the Triassic basin. 



Close of the Appalachian Revolution, Figure p. The pre- 

 vious views have been based upon various lines of evidence which 

 give a considerable knowledge of the character of the land sur- 

 faces of the periods involved; but, upon leaving behind us the 

 Mesozoic era, all such detailed knowledge fails us. Erosion has 

 removed vast thicknesses of the Paleozoic rocks, and all that 

 remain have been altered and crystallized by heat and mashed 

 by irresistible forces while still buried deep within the earth. 

 Such metamorphic rocks are the exposed foundations of ancient 



