486 - MR. P, F, KENDALL ON A SYSTEM OF [Aug. 1902, 
marginal overflow has bifurcated in consequence of a slight recession 
of the ice permitting the water which was flowing in contact with 
it along a hillslope to take a lower course. The other cause of 
dichotomy at the outfall I have observed only in the Cheviots. The 
ease is that of a pair of lakes, with an intervening spur terminated 
near the ice-margin by a bold knob. The spur is cut behind the 
knob by a deep overflow-channel, at the outfall of which a great 
gravel-delta has been thrown down. The outlet was at first pro- 
bably over the convex fan of deltaic material, but with a shrinkage 
of the ice and corresponding lowering of the lake-level, the flow - 
took place along each side of the delta; then a further recession of 
the ice allowed the lower lake to drain off through a marginal 
channel, and this gave an advantage to the outfall nearest to the 
ice, which therefore became the sole outlet. These features are 
precisely repeated in two adjacent valleys, Monday Cleugh and the 
gorge behind Hambleton: the marginal outflows can be seen, and 
I therefore feel some confidence in the explanation.’ 
A remarkable and striking effect of fluctuations in the edge 
of the ice, both in advances and retreats, is the production of 
deserted oxbows. These features are peculiar to marginal 
overflows, never occurring in direct overflows. When the 
advance of a lobe of ice causes an obstruction of a marginal outflow 
at one point, then an ‘in-and-out’ crescentic valley is carved in 
the opposing hillside to connect the two portions of the valley. This 
new portion may be cut to such a depth as to become the permanent 
channel: the part obstructed by ice will therefore never come into 
use again, and on the withdrawal of the ice may appear as a high- 
level loop many feet (50 or more) above the functional channel. 
Such a case is to be seen at Brown Rigg, near Robin Hood’s Bay. 
The more frequent case, however, is that in which the new channel 
has not been cut so deeply as the old one. In these instances, the 
withdrawal of the ice has reopened the main channel, and the new 
bow has been abandoned. The main valley continues to deepen so 
long as it is in use, and the abandoned bow will remain in singular 
isolation. Evan-Howe Slack, a quarter of a mile from Brown Rigg 
(see Pl. XX VI), and the channel which isolates Castle Rigg, in the 
Moss-Swang overflow near Goathland (see fig. 8, p. 510, & Pl. XXIT) 
present examples of this type. 
The last feature which it is necessary to mention, is that these 
deserted channels, as well as the other type of anomalous valleys 
(those which now carry one of the main streams of the district), never, 
or very seldom, receive any considerable tributaries; and when they 
do, there are usually manifest signs that the tributaries belong to a 
drainage which was on a much higher plane before the time when 
the anomalous valley was cut. 
Newton Dale, which has served so often as an illustration, may 
1 Details of these will be found ina paper, by Mr. H. B. Muff and the author, 
read to the Edinburgh Geological Society on March 20th, 1902. 
2 
