252 HISTORICAL GEOLOGY 



except potentially in the hidden differences of hardness or rock 

 structure. Such conditions prevailed over a very large region — 

 certainly all of the eastern portion of the United States." x 



The Cretaceous period was closed in eastern North America by 

 a disturbance which produced an upwarp of this vast Cretaceous 

 peneplain with maximum uplift of from 2000 to 3000 feet, follow- 

 ing the general trend of the Appalachians and thence through 

 northern New York and western New England. This upward 

 movement was unaccompanied by any renewed intense folding of 

 the strata, the effect having been to produce a broad dome sloping 

 eastward and westward, and northward to the Gulf of St. Lawrence 

 and southward to the Gulf of Mexico. The upward movement 

 was, however, accompanied by the retreat of the sea from the 

 Coastal Plain area, which thus accounts for the widespread uncon- 

 formity there between the Cretaceous and the overlying Tertiary 

 strata. 



Another prominent effect of this great uplift was to revive the 

 activity of the streams so that they once more became active 

 agents of erosion, and the present major topographic features of 

 the eastern United States have been largely produced by the 

 erosion and dissection of this upraised Cretaceous peneplain. 

 Where the peneplain was best developed, the typical Appalachian 

 ridges and valleys, running parallel to the trend of the mountain 

 range, are now beautifully shown. These valleys are the trenches 

 of the upraised peneplain, while the ridges have developed along 

 the belts of hard rock, their summits actually representing portions 

 of the old peneplain surface (Fig. 155). These ridges all rise to 

 the same general level for miles around, and as viewed from the 

 summit of any one of them, the concordant altitudes give rise to 

 what is called the "even sky-line," which is a most striking feature 

 of the landscape. In New York state and western New England 

 remnants of the upraised peneplain surface are also distinctly 

 shown. 



Foreign Cretaceous 



Europe. — Toward the close of the Jurassic and about the 



beginning of the (k-p.t^iaceous, continental deposits were forming 



in parts of central and western Europe. Often these deposits 



grade from the Jurassic into the earliest Cretaceous. The Alpine 



1 C. P. Berkey: N. Y. State Mus. Bull. 146, p. 67. 



