THE WORK OF STREAMS 



115 



The peneplain of the Rhine district near St. Goar, in which the Rhine 

 has cut a shallow valley. (Photo. D. W. Johnson.) 



gneisses, and schists had been cut down to a comparatively level 

 plain, above which stood some hills a few hundred feet high, such as 

 Mt. Monadnock, Mt. Greylock, and Mt. Wachusett. When this 

 peneplain was raised and the streams again began to erode, the weak 

 sandstones were quickly cut away, leaving the trap rocks standing 

 as the Holyoke and other trap ranges of the Connecticut valley, 

 and the old crystalline rocks bounding the " valley " as the high- 



Fig. 103. — Peneplain with several monadnocks in the distance. 

 Camp Douglas, Wisconsin. (Sankowsky.) 



Neai 



lands. In the highlands, streams have cut deep and usually narrow 

 valleys. The higher hills have about the same altitude, except that 

 the surface of the ancient peneplain rises to the northwest ; on Long 

 Island it is at sea level, but its height increases to an altitude of 

 about 1500 to 2000 feet in Vermont and New Hampshire. Mt. 



