44 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



Near the railroad a rock outcrop was found which gives a 

 clue to the nature of the broad lowland. The rock consists 

 mainly of schist, but on the side next the valley there is a facing 

 of rotten limestone. This plain, like all the others in this region, 

 is a local peneplain developed on soluble limestone. A better 

 example could not be found to prove the fallacy of the saying 

 that " a broad valley proves the existence of a large river." The 

 plain is simply a local expansion of a valley which on each side 

 is much narrower. No other river than the one flowing through 

 it can have been responsible for the erosion, for the plain is en- 

 closed by hills of gneiss and schist (PI. III). 



At Mill Plain the valley is crowded by ragged rock outcrops 

 which jut into the lowland. Here the river occupies a ravine 

 cut in till near the north side of the valley. West of Mill Plain 

 station the valley is encumbered with ridges of stratified drift, 

 interspersed with heavy accumulations of till. Near Andrew 

 Pond the true width of the valley one-eighth mile is shown 

 by rock outcrops on both the north and south slopes. The valley 

 at this point gives no indication of narrowing toward the head- 

 waters ; in fact, it becomes broader toward the west. 



Between Andrew Pond and Haines' Pond is the divide which 

 separates the waters of the Still system from those of the Croton. 

 It consists of a jumbled mass of morainal hills, seemingly of 

 boulder clay, that rise from 50 to 60 feet above the level of the 

 ponds. The divide is thus merely a local obstruction in what 

 was formerly a through drainage channel. ^V^o 



THE STILL-CROTON VALLEY 



It is evident that before the advent of the glacier a stream 

 must have flowed through the Still-Croton valley past the present 

 divide in order to have excavated the rock valley there found. 

 The Housatonic could not have flowed west through this valley 

 if it was as narrow and shallow as is indicated by known rock 

 outcrops; the river could have flowed through it only in a deep 

 narrow gorge which was later buried under drift, but the evidence 

 at hand does not support this view. 



It is most probable that this valley was made by the preglacial 

 Croton River. This explanation demands no change in the direc- 

 tion of Still and Croton Rivers but calls for a divide at some point 



