No. 30.] STILL RIVER. 45 



east of the present one. From a divide between the Fair Grounds 

 and Danbury, a small stream may be supposed to have flowed 

 toward the east, joining the larger northern branch of the Still 

 at a point near the middle of the city of Danbury. The stream 

 flowing westward from this divide formed the headwaters of one 

 branch of the Croton system. 



The presence of till in a ravine can be used as a criterion for 

 locating the site of a former divide, for where till is present in 

 the bed of a stream the channel is of preglacial date. Where 

 the river crosses a divide it should be cutting through rock, though 

 till may be present on the valley slopes. Judged by this test, 

 the old divide was situated either just east of the Fair Grounds 

 plain or at the east end of the ravine described in the preceding 

 topic. Of these two positions the one near the Fair Grounds 

 seems the more likely (fig. i), for at this place the river has 

 excavated a recent channel with steep sides in gneissoid rock. 

 The absence of the limestone at this point may be sufficient in 

 itself to explain the location of the divide. 



Exact measurements of the drift in the upper Still valley 

 are needed in order to establish this hypothesis completely and to 

 plot the old channel, but the position of the rock floor of the 

 former channel extending westward from the Fair Grounds may 

 be fixed approximately. The rock at the assumed divide now 

 stands at 420 feet ab.ove sea-level and it is reasonable to assume 

 that ten feet has been removed by glacial scouring and post- 

 glacial erosion, making the original elevation 430 feet. The 

 present divide between Andrew Pond and Haines' Pond has an 

 elevation of 460, but the bedrock at this place is buried under 

 60 feet of drift, so that the valley floor lies at 400 feet. Accord- 

 ing to these estimates the stream which headed east of the Fair 

 Grounds had a fall of 30 feet before reaching the site of the 

 present Haines' Pond (fig. 8, B). 



GLACIAL LAKE KANOSHA 



When the Croton Branch was beheaded by drift choking up 

 its valley west of Andrew Pond, the ponded waters rose to a 

 height of from 20 to 30 feet and then overflowed the basin on 

 the side toward Danbury. The outlet was established across the 

 old divide, and as the gorge by which the water escaped was cut 



