8 ANNALS NEW YORK ACADEMY OF SCIENCES 



mature valleys have been opened out below the general upland by such 

 streams as the Saco Eiver and the Merrimac and its tributaries. 



When consideration is given to the final stage of a stream's history, 

 that of old age, after erosion has reduced the entire drainage basin to 

 an almost flat surface, the instructor is able to place before his class an 

 unparalleled example in the New England peneplane (Fig. 4). The 

 even crest of the Palisades truncating the westward dipping formations, 

 and impressive for this reason, serves as an illustrative example close at 

 home. Throughout New England, the Hudson Highlands, Schooley 

 Mountain, the rest of the Highlands of New Jersey, and Kittatinny 

 Mountain, the even crest lines of the folded ridges of Pennsylvania, and 

 the Blue Eidge of Virginia this same peneplane finds expression and is 

 known variously as the New England, the Schooley, the Kittatinny, and 

 the Cretaceous peneplane. It is true that this peneplane no longer stands 



Mt.Greylock Mt. Haystack^ 



The New England Upland 

 in western Massachusetts 

 field sketch 



Fig. 4. — Sketch of Netv England peneplane having an elevation of 1^00 feet in 

 western Massachusetts 



As seen looking west from Mt. Massaemet, near Shelburne Falls. Two or three 

 monadnocks rise above the peneplane, and the Deerfield River has incised itself several 

 hundred feet below that level. 



at the level to which it had been reduced. The fact that it has been 

 elevated only makes it the more valuable as an object for study. It pro- 

 vides an example when rejuvenation and the matter of several cycles are 

 discussed. The gorge of the Deerfield Eiver (Fig. 4) and many other 

 New England streams cut below the upland level serve to illustrate the 

 essential features of a topography first reduced to old age and then dis- 

 sected as a result of later uplift, but even still finer examples are to be 

 had in the case of the Monongahela Eiver in Pennsylvania with its great 

 swinging meanders incised below the Cretaceous peneplane of the Alle- 

 ghany Plateau, and the really remarkable entrenched meanders of the 

 Potomac Eiver in its course through the folded mountains of Maryland 

 whose crests still preserve that upland level. To carry out still further 

 the idea of repeated uplift with renewed erosional activity in each cycle 

 reference is made to the three cycles so well displayed throughout the 

 folded Appalachian belt (Figs. 15, 16, 17, 19, 20). The old stage result- 

 ing in the Cretaceous peneplane on the summits marks the first cycle, 

 a second and post-mature stage resulting in the Tertiary peneplane 



