380 THE JOURNAL OF GEOLOGY 



where the river leaves the limestone valley, which continues to 

 the southwest, and flows for ten miles in a narrow gorge in the 

 gneiss, only to again enter at its northern end a long narrow bed 

 of limestone. The following seems to be the probable explan- 

 ation. When the land stood at the elevation represented by the 

 Cretaceous peneplain, these hard beds were below or' but very 

 slightly above baselevel, and were therefore undiscovered by the 

 stream or had just begun to make themselves known late in the 

 cycle. Had they been reached early in the cycle, when the stream 

 was far above baselevel and presumably before many of its tribu- 

 taries had been developed, and when it was therefore a smaller 

 river, it is quite probable that further re -adjustments would have 

 occurred, and the stream been led away from the hard rocks onto 

 the softer beds to the west ; but when they were reached the 

 stream had cut so deeply and so nearly to baselevel that it was 

 safe from capture. After the elevation of the peneplain the 

 stream was revived and disclosed more and more of these hard 

 beds, but was then, owing to the development and head -water 

 growth of its tributaries, too important a river to be diverted by 

 any rival. A river of this kind may be said to be " conformably 

 superimposed" in distinction to one which is superimposed from 

 an uncomformable cover. 



Revived streajns. It is important to recognize the effect of the 

 post -Cretaceous uplift upon the rivers at that time established. 

 As the land was baseleveled and the velocity of the streams de- 

 creased, they lost in large degree their cutting power and 

 sluggishly meandered more or less in broad flood-plains. During 

 and for a period after the uplift, their cutting power was restored 

 to them by virtue of their increased velocity and they excavated 

 the deep narrow valleys which we find in the crystalline high- 

 lands. The upper course of the Housatonic is a good example 

 of a river re -adjusted to the structure during one cycle, revived 

 by uplift to a second cycle of erosion, and in places "conform- 

 ably superimposed" upon structures from which it would have 

 been led away in the ordinary course of re - adjustment. Its 

 tributaries, the East Aspetuck, Still, Shepaug, and Pomeraug 



