MODERN ACTION OF RIVERS. 
373 
Whatever may have been the causes which closed the old channel, there can remain no 
doubt of the mode in which the new one was formed. We can think of no other cause than 
the action of the stream itself, that would excavate such a channel, with vertical walls, and in 
a direction so devious. If it were of the age, and formed by the same means as the majority 
of valleys, it would be broader in proportion to its depth, and its sides and bottom present 
some deposits of drift. Where the stream emerges into an old valley on the north, near 
Rogers’ bridge, after making this circuit, a distance one-third as great, direct from Portage, 
would have brought the stream through the old valley filled with drift. Between Rogers’ 
bridge and St. Helena the direct route is filled with drift, while the river channel is a narrow 
deep gorge, making a circuit of three miles. Again, for three miles before reaching Mount- 
Morris, the same devious course is pursued, and the banks are almost equally precipitous, 
though, from being shales, they are less abrupt. In all these instances the banks bear the 
marks of a freshness of excavation not to be mistaken. It is emphatically a modern channel. 
178. 
The accompanying illustration represents the course of the 
river from Portage to St. Helena ; a direct line between the 
two places would have passed in an ancient valley, while all 
the deviations are through rocky strata, and in deep gorges. 
a. Position of the lower falls of Portage. 
This example is sufficient to enable us to understand how a river, when obstructed in one 
direction, will excavate a channel in another; and even, though the obstruction be only loose 
materials, it often finds an easier course by wearing down hard rocks than by removing gravel 
and sand; making a circuitous route through solid strata, while a more direct one would 
have been through a superficial deposit. 
Nearly every stream flowing from the south, over strata of this age, presents the same 
features, in a greater or less degree. A hundred examples can be cited where there is 
