l8 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



Rocky River are developed on Stockbridge limestone. The lower 

 valley of Rocky River is, however, mapped as Becket gneiss and 

 Thomaston granite gneiss. Although the only outcrops along 

 lower Rocky River are of granite, it is believed that a belt of lime- 

 stone or schist, now entirely removed, initially determined the 

 course of the river. The assumption of an irregular belt of 

 limestone in this position would account for the series of gorges 

 and flood plains in the vicinity of Jerusalem bridge and for the 

 broad drift-filled valley at the mouth of Rocky River. These 

 features are difficult to explain on any other basis. 



JUNCTION OF ROCKY AND HOUSATONIC RIVERS 



One of the distinguishing features of Rocky River is the 

 angle at which it joins the Housatonic (fig. i). The tributaries 

 of a normal drainage system enter their master stream at acute 

 angles, an arrangement which involves the least expenditure of 

 energy. Rocky River, however, enters the Housatonic against 

 the course of the latter, that is, the tributary points upstream. 

 Still River and other southern tributaries of the Housatonic 

 exhibit the same feature, thus producing a barbed drainage, 

 which indicates that some factor interfered with the normal 

 development of tributary streams. Barbed drainage generally 

 results from the reversal of direction of the master stream 1 , but 

 it is impossible to suppose that the Housatonic was ever reversed. 

 As will appear, it is an antecedent master stream crossing the 

 crystalline rocks of western Connecticut regardless of structure, 

 and its course obliquely across the strike accounts for the peculiar 

 orientation of its southern tributaries, which are subsequent 

 streams whose position is determined by the nature of the rock. 

 For the same reason, the northern tributaries of the Housatonic 

 present the usual relations. 



ABNORMAL PROFILE 



The airline distance from the bend in Rocky River at Sherman 

 to its mouth at the Housatonic is 2^4 miles, but the course of the 



1 Leverett, Frank, Glacial formations and drainage features of the Erie and Ohio 

 basins: U. S. Geol. Survey Mon. 41, pp. 88-91, figs. 1 and 2, 1902. See, also, the 

 Genoa, Watkins, Penn Yan, and Naples (New York) topographic atlas sheets. 



