No. 3O.] STILL RIVER. 37 



The northern part of Still River valley has not the typical 

 U form which results from glacial erosion. As contrasted with 

 the U-shaped glacial valley and the V-shaped valley of normal 

 stream erosion, it might be called rectangular so sharply does the 

 flat valley floor terminate against the steep hillsides. The floor 

 is too smooth and flat and the tributary valleys too closely adjusted 

 to the variant hardness of the rocks to be the work of such a 

 rough instrument as the glacier. A level so nearly perfect as 

 that of the flood plain is the natural result of erosion of soft 

 rock down to a baselevel, whereas glacial scouring tends to pro- 

 duce a surface with low rounded hills and hollows. 



Overdeepening would be expected, because glaciers erode 

 without reference to existing baselevels. That a river .valley 

 should be cut out by ice just enough to leave it graded with 

 respect to the main valley would be an unusual coincidence. 

 This is what is found where the Still River valley joins the 

 Housatonic, and it indicates normal stream erosion. Also, if 

 the limestone of the northern Still River valley were gouged out 

 by the glacier, the action would in all probability have been 

 continuous in the limestone belt to the north of the Housatonic, 

 and where the belt of soft rock crosses the Housatonic the river 

 bed would be overdeepened. Although the valley of the Housa- 

 tonic near New Milford is very flat, as is natural where a river 

 crosses a belt of weak rock, the outcrops are sufficiently numerous 

 to show that it has not been overdeepened. The limestone area 

 along the East Aspetuck is largely overlain by till, but here again 

 the presence of rock in place shows that the valley has not been 

 overdeepened. Moreover, limestone boulders in the southern 

 part of Still River valley are not as abundant as they should be 

 under the hypothesis that the northern part had been gouged out 

 .extensively. 



That the northern part of the Still River valley was not deeply 

 carved by ice is shown also by the character of the tributary 

 streams. The three small 'brooks on the west side of the valley, 

 near Beaver Brook Mountain, were examined to see if their 

 grades indicated an over-deepening of the main valley. These 

 streams, however, and others so far as could be determined, 

 were found to have normal profiles ; that is, their grades become 

 increasingly flatter toward their mouths. The streams are cut- 



