POST-JURASSIC HISTORY OF THE NORTHERN APPALACHIANS 691 



did not reach the Coastal Plain, should correspond to intervening formations. 

 Warping is shown to have progressed variably, but without reversal, during 

 the periods involved. Thus physiography, stratigraphy, and structural geology 

 give three converging methods for testing sequence and age — the province of 

 historical geology. The several divisions of the science are interlocked and 

 render mutual support. 



The sequence of regional events during post- Jurassic time is shown to be 

 determined with considerable probability as follows : 



Comanche. — Intermittent interior uplift reaching large amount, marginal 

 downwarping, and continental sedimentation. 



Cretaceous (Upper Cretaceous). — The sea invades the Appalachians for the 

 first time since the Paleozoic, but now from the ocean instead of the conti- 

 nental interior. At the maximum of transgression its waves cut the Becket 

 terrace against the southeast side of the Green Mountains and the south side 

 of the Catskills. This was followed by emergence of several hundred feet, a 

 crustal stability for a considerable period, and the cutting of the Canaan ter- 

 race. Both of these terraces appear to be distinctly older than the following 

 series; so that, as the next is probably Oligooene, these may be tentatively 

 regarded as probably middle and late Cretaceous respectively. 



Eocene. — Emergence of several hundred feet and retreat of the shore to the 

 region of the present Coastal Plain. Long period of subaerial erosion. 



Oligocene. — Probable date of submergence and development of the Cornwall 

 terrace. 



Miocene. — Emergence of several hundred feet. Erosion of inner portion of 

 Oligocene from the Coastal Plain, followed by submergence of present coastal 

 plain and edge of the present Piedmont Plateau either at end of Miocene or 

 early Pliocene. No terrace recognized. 



Pliocene. — Intermittent uplift and retreat of the sea ; cutting of the Goshen, 

 Litchfield, and Towantic terraces. The Appomattox (Lafayette) terrace, still 

 preserving in part its surface deposits, is 200 feet below the Towantic and is 

 probably late Pliocene in age. Below the Appomattox, or Lafayette, are the 

 fainter Pleistocene terraces. 



An uplift of a few hundred feet was all that was necessary at any time to 

 cause a retreat of the shore from these high-level terraces to the region of the 

 present Coastal Plain, since the present great difference in elevation is mostly 

 due to later progressive warping. Similarly, intervening phases of slight sub- 

 mergence and crustal rest are sufficient to account for the planing inland by 

 the sea. The sequence of events thus indicates progressive but oscillatory up- 

 lift during Tertiary time, becoming more rapid in the Pliocene and Pleistocene. 

 The conclusions, as in the previous paper, rest largely on an analysis of the 

 profiles. 



Discussion 



Prof. D. W. Johnson pointed out that if we have an uplifted and tilted 

 peneplain on which there are monadnock residuals, it is possible to select posi- 

 tions in which terrace profiles can be drawn similar to some of those on which 

 Professor Barrell bases his conclusions in favor of marine planation. Accord- 

 ing to the theory of marine planation, what are now generally regarded as 

 monadnocks are to be interpreted as stacks on the wave-cut plain, and should 



