and the Geology of the Surrounding Country. 117 



Passing lower down on the Genesee river, there are other 

 places where the stream has left the old channel, now filled 

 with d/ift, and formed a new one, through rocky strata ; and 

 finally, at Mount Morris, it emerges into another ancient val- 

 ley from a narrow gorge bounded by mural escarpments. ^ 

 would be absurd to assert, that broad valleys, with slopin£3 

 sides, filled, or partially filled with drift, are of the same age, or 

 due to the same agency, as the narrow, deep valleys or chasms 

 with clean, rocky embankments, and containing no other loose 

 materials than those arising from the adjacent rocks. 



Similar examples may be found in the outlets of Seneca 

 and Cayuga Lakes, which flow into Lake Ontario. Now the 

 course of t?iese outlets is not in a direct line north to the 

 lake, but from Seneca it turns to the eastward, excavating its 

 course through the limestone and gypsum beds, between that 

 lake and Cayuga. From all examinations I have made, there 

 appears to be an ancient valley, filled with drift, between the 

 northern end of Seneca Lake and Ontario ; and yet, notwith- 

 standing this, the stream has excavated harder materials, and 

 taken a much more circuitous route to Lake Ontario. The 

 same explanation may be given of Canandaigua and the outlets 

 of other lakes. 



As an analogous case, we may compare the ravine of St. 

 Davids and the whirlpool, with that of Iroudequoit, a few 

 miles east of Rochester. The Genesee river, after leaving 

 the gorge at Mount Morris, flows in the bottom of an ancient 

 valley to within a short distance of Rochester, where it enters 

 a new channel. This channel is narrow, with almost perfect 

 mural banks, and nowhere contains deposits of drift. On the 

 lake shore, about two miles east of the mouth of the Genesee, 

 we find a broad and deep ravine, known as the Iroudequoit 

 bay. This ravine is excavated to an unknown depth below 

 the level of Lake Ontario. The Iroudequoit creek which 

 takes its rise in the southern part of the county, flows through 

 this ravine for a few miles before reaching the lake. This 

 ravine pref^ents a very dilferent appearance from either that of 

 the Genesee below Rochester, or of the Niagara, and no one 

 could suppose that the present stream had ever excavated such 



