136 Scientific Geology. 



This peculiar arrangement of the sides of valleys, although 

 scarcely ever noticed by geological writers in this country, appear to 

 be very common on both sides of the Atlantic. Dr. Bigsby notices 

 a striking case in Lower Canada ; and Dr. Macculloch represents 

 them as numerous in Scotland. They appear to be a distinct phe- 

 nomenon from the Parallel Roads, so ably described by the last 

 named writer.* 



No observer will doubt but terraced valleys were produced, in some 

 way or other, by the streams that now flow through them. And it is 

 natural to impute them to the sudden bursting of the barriers of a 

 pond or lake, through which the stream flowed ; or to the sudden re- 

 moval of an obstruction in a river, whereby its bed was rapidly 

 deepened in soft soil, higher up the stream than the obstruction. If, 

 for instance, the greenstone barrier through which Deerfield and 

 Westfield rivers now pass, had been suddenly sunk a number of feet 

 by some convulsion of the earth, or powerful ice flood, their beds 

 would have been rapidly sunk by the waters in the soft meadows 

 above the barriers ; and thus terraces might have resulted. But I 

 may be permitted to doubt whether any such sudden reduction of the 

 river's bed is necessary to account for this phenomenon. 



Let us suppose a period, when the bed of Connecticut river, in the 

 mountainous region below Middletown, was yet so elevated as to 

 ^ause the waters to overflow the great basin between New Haven 

 and Vermont. At that time, the mouths of Deerfield and Westfield 

 rivers would have been on the western margin of this lake, or in the 

 places where they now issue from the primary mountains. As the Con- 

 necticut wore down its bed, the lake would gradually drain off, leav- 

 ing the tertiary formation, which its waters had deposited, perhaps 

 100 feet thick upon an average, with an almost entirely level surface. 

 The Connecticut, having found its present bed, and the waters being 

 drained from the valley, Westfield and Deerfield rivers must also ex- 

 cavate beds in the tertiary formation, above described, in their course 

 to the Connecticut. Their course would no doubt at first be ex- 

 tremely serpentine, as that of rivers usually is, in flat countries. But 

 as the bed of the Connecticut gradually sunk lower and lower, so 

 would the beds of its tributaries sink : and then, would their waters, 

 often swollen by rains and obstructed by ice, begin to wear away the 

 the projecting banks, and convey them into the Connecticut. At 



* Geological Translations, Vol. IV. p. 314. 



