l6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



In spite of its rapid current, however, the river is unable to move 

 these boulders, and for nearly three miles one can walk dry-shod 

 on those that lie in midstream. 



At two or three places below Jerusalem, in quiet reaches 

 above rapids, the river has taken its first step toward making a 

 flood plain by building tiny beaches. One-half mile above the 

 mouth of the river the valley widens and on the gently rising 

 south bank there are several well-marked terraces about three 

 feet in height and shaped out of glacial material. A delta and 

 group of small islands at the mouth of Rocky River indicate the 

 transporting power of the stream and the relative weakness of 

 the slow-moving Housatonic. 



RELATIONS OF THE VALLEY TO GEOLOGIC STRUCTURE 



Rocky River is classed with streams which are comformable 

 to the rock structure. This conclusion rests largely on the 

 analogy between Rocky River and other rivers of this region. 

 The latter very commonly are located on belts of limestone, or 

 limestone and schist, and their extension is along the strike. 

 The interfluvial ridges are generally composed of the harder 

 rocks. The valleys of the East Aspetuck and Womenshenuck 

 Brook on the north side of the Housatonic, and of the Still, the 

 Umpog, Beaver Brook, the upper Saugatuck, and part of Rocky 

 River are on limestone beds (fig. 2). In the valleys between 

 Town Hill and Spruce Mountain (south of Danbury), two 

 ravines northwest of Grassy "Plain (near Bethel), and the 

 Saugatuck valley north of Umpawaug Pond, the limestone bed 

 is largely buried under drift, talus, and organic deposits, but 

 remnants which reveal the character of the valley floors have been 

 found. The parallelism between the courses of these streams 

 and that of Rocky River and the general resemblance in the 

 form of their valleys, flat-floored with steep-sided walls, as well 

 as the scattered outcrops of limestone in the valley, have led to 

 the inference that Rocky River, like the others, is a subsequent 

 stream developed on beds of weaker rock along lines of foliation. 



The Geological Map of Connecticut 1 shows that the valleys 

 of Still River, Womenshenuck Brook, Aspetuck River, and upper 



Gregory, H. E., Robinson, H. H., Preliminary geological map of Connecticut; 

 Geol. and Nat. Hist. Survey. Bull. 7, 1907. 



