; eT ee ee 
81 
valley that it excavated, and that it occupied for so long, remains 
to this day, as an eloquent witness of the former magnitude of the 
Greta. Other rivers of the Lake District have had much the same 
history. I have already noticed the curious history of the Petteril 
in this connection.* In this river an additional complication was 
introduced in the shape of two transverse channels developed 
across the old river course along the outcrop of easily-wasted rocks, 
thereby cutting the river itself into ¢ivee, and letting off the water 
in new directions. 
Up to a certain point rivers are able to fret their way across an 
escarpment pari passu with its own rate of development, pro- 
vided that the rate of durability of the stratum forming the 
escarpment does not differ very greatly from that of the less 
durable strata above and below, to whose higher rate of waste 
its development is due. But where the nascent ridge owes its 
development to the weathering of strata whose relative durability 
is very low, such a ridge tends to develop, first, into a barrier 
across the river, and, eventually, into a new watershed, the severed 
parts of the old stream then flowing away from that ridge in 
opposite directions, and leaving an inosculating valley as a record 
of this part of its history. The sequence of events that have given 
rise to inosculating valleys in this district finds its parallel in many 
other areas of mountain drainage where the rivers have traversed 
rocks whose several rates of destructibility have varied greatly. 
Another point of interest bearing upon the history of the Eden 
_is the great variety in the character of any given valley, according 
_ to the nature of the rocks it traverses. The formation of a river- 
_ valley is dependent to a much greater extent upon waste of 
the surface by subaerial causes aided by the transporting action of 
the river than by the direct erosive action of the river itself. 
_ Subaerial denudation acting alone, affects the whole surface, con- 
stantly tending to reduce all inequalities to the general level of the 
sea. Its action, like that of the sea, may therefore be regarded as 
Mainly lateral. Rivers, on the other hand, by removing the 
material detached by weathering, tend to facilitate the destructive 
* Trans. Cumb. and West. Assoc,, No, XIII. p. 89. 
6 
