No. 30.] ROCKY RIVER.. 25 



At the point marked No. 7+1000, about i 1 /^ miles from the 

 mouth of Rocky River, the evidence derived from 8 drill holes, 

 bored at distances ranging from 200 to 550 feet from the right 

 'bank, shows the drift cover to be from 48 to 72 feet in thickness. 

 At 200 feet from the river the drill passed through 72 feet of 

 sand, clay, and gravel before striking rock at 303 feet above 

 sea-level. 



At No. 7, about one mile from the mouth of Rocky River, a 

 hole drilled 415 feet from the right bank showed 58 feet of drift, 

 consisting of clay, sand, gravel, and boulders. The drill reached 

 rock at 342 feet, which is the figure given 'by R. E. Dakin for the 

 elevation of the river at this point. Drill holes made, respec- 

 tively, at 50 and 60 feet to the right of this one showed a drift 

 cover of 61 feet, so that the underlying rock rises only 4 feet in a 

 distance of 475 feet to the east of the river. 



The foregoing evidence, showing a rock level at D 98 feet 

 lower than that at No. 7, leaves no doubt that the preglacial 

 course of Rocky River was to the south from No. 7, and there is 

 nothing in the topography between Jerusalem and Danbury to 

 make improbable the existence of a buried channel; 



EFFECT OF GLACIATION 



The preglacial history of Rocky River as outlined assumes 

 that before the glacier covered this part of Connecticut the 

 present lower course of Rocky River was separated from the 

 rest of the system by a divide situated somewhere between the 

 present mouth of the river and the mouth of Wood Creek. It 

 remains to be shown by what process Rocky River was cut off 

 from its southern outlet into Still River and forced up its 

 eastern branch and over the col into a* tributary of the Housa- 

 tonic. Though the preglacial course of Rocky River appears 

 to be more natural than the present one, it is really a longer 

 course to the Housatonic ; the older route being 32 miles, whereas 

 the present course is 19 miles. This fact explains, in part, why 

 the glacier had little difficulty in altering the preglacial drainage, 

 and how the change so effected became permanent. Eccentric as 



