GEOLOGY 
gorge of the Eden, extending from Eden Lacy past Nunnery Walks and 
Armathwaite, offers an excellent illustration of this principle ; and others 
little inferior to this occur elsewhere in the county. 
The same principle which enables a river to cut its way from soft rocks 
across harder, on a small scale, is identical with that which has come into 
action on the larger scale under consideration. All that is needed in the 
initial stages is that the rock through which the river is cutting down to 
the harder mass beneath shall remain long enough to establish the stream in 
its new course, and that the rock on either side of the gradually-developing 
ridge shall not waste at a faster rate than the river can keep pace with in 
its work of excavating the gorge. It must be obvious that if the area 
above the gorge should happen to waste at a more rapid pace than the | 
gorge is being excavated, there must presently come a time when the 
river can no longer carry on that work, but, instead, must find egress to 
the sea by another channel. In this case the river is severed in two ; the 
middle of the gorge becomes the watershed of the lower half of the 
original river, and after a time usually sends a small tributary to the 
parent stream, which may eventually for a distance flow in a direction 
diametrically opposite to that which it had at first. 
(f) The somewhat complex and apparently theoretical section just 
ended is inserted here with the object of explaining some very anomalous 
features which characterize many of the valleys of Cumberland. Fore- 
most amongst these features are the many so-called ‘ inosculating ’ valleys 
already referred to, and which occur in various parts of the district. 
What is meant by that term is that there are often two streams flowing 
in opposite directions in what is manifestly one and the same valley, 
which therefore runs continuously across the present watershed. Nearly 
all the main roads, and most of the railway routes traversing mountain 
districts follow inosculating valleys. The pass at Dunmail Raise, which 
is traversed yearly by thousands of tourists, may serve as an example. 
Briefly, they may be explained as due to a gradual displacement of the 
watershed, as the surface has been lowered and the river has encountered 
rocks showing different combinations of durability from those in which 
its course has been originally established. Some of the rivers of Cumber- 
land may have been severed in this way at more than one place. The 
Petteril, for example, probably originated near where Matterdale is now, 
and flowed north-eastward to join the Eden west of the present course of 
that river near Great Salkeld. But two sets of depressions have originated 
across its original course, or, what comes to the same thing, two sets of 
ridges have been developed at a rate faster than the erosive power of the 
Petteril could keep pace with. As a consequence the upper half of the 
Petteril has been diverted into one of these growing depressions and now 
joins the Eamont below Ullswater. A new watershed has arisen in what 
is now Greystoke Park, and the Petteril goes on in its original channel from 
there to near Catterlen. Furthermore, with the continued waste of the 
surface, the gradual evolution of the great ridge of Penrith Sandstone 
forming Lazonby Fell has proceeded at a rate more rapid than the river 
I 49 . 
