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



is the route followed by the Danbury and Norwalk Division of 

 the Housatonic Railroad. It is natural to assume that the Housa- 

 tonic might have occupied any one of these lines of valleys, 

 particularly where they are developed on limestone and seem too 

 broad for the streams now occupying them. Nevertheless, al- 

 though each of these routes is on soft rock and some give 

 shorter distances to the sea than the present course, it is highly 

 improbable that the Housatonic ever occupied any of these valleys. 

 For had the river once become located in a path of least resist- 

 ance, such as is furnished by any of these suggested routes, it 

 could not have been dislodged and forced to cut its way for 25 

 miles through a massive granitic formation, as it does between 

 Still River and Derby, without great difficulty (PL IV, A). 



Ari inspection of the larger river systems of Connecticut 

 shows that the streams composing them exhibit two main trends. 

 Likewise, the courses of the larger rivers themselves, whether 

 trunk streams or tributaries, combine these two trends, one of 

 which is northwest-southeast and the other nearly north-south. 



The north-south drainage lines are the result of geologic 

 structure, and many broad, flat-floored valleys, often apparently 

 out of proportion to the streams occupying them, have this direc- 

 tion. On the other hand, the northwest-southeast drainage lines 

 across the strike of formations, coincide with the slope toward 

 the sea of the uplifted peneplain whose dissected surface is repre- 

 sented by the crests of the uplands. The valleys of streams with 

 this trend are generally narrowband some are gorges where re- 

 sistant rock masses are crossed. The northwest-southeast trends 

 of master streams thus were determined initially by the slope of 

 the peneplain, whereas the north-south trends represent later 

 adjustments to structure. 



It is concluded, therefore, that the Housatonic between Bulls' 

 Bridge and Derby (fig. 10), had its course determined by the 

 slope of the uplifted peneplain and is antecedent in origin. The 

 old headwaters extended northwest from the turn in the river 

 near Bull's Bridge, whereas that part of the river above Bull's 

 Bridge was initially a minor tributary. This tributary, because 

 of its favorable situation, in time captured all the drainage of 

 the extensive limestone belt to the north and then became part of 

 the main stream. The lower Housatonic, therefore, has always 



