Olahke and WTLUAArs. — Gfolofiy of T)ailinf/ Bapge. 
165 
sevei'al riglit-;ni|;l(‘il bonds in tbo vnlloy, the norlli-south arms of 
■\vliicdi JU'e ]>n)bably ]K)rtioiis of tlu' ohler rlisiueinbcved drainage 
system. The tri])utarios, ^vhi(•)l goiuTally have* a more or less 
north-south direction, flow for tlio greater part of their course 
through sliallou' wide valleys, but their lower ])arts flow through 
narrow deeji valleys. What length of a tributary is thus rejuve- 
nated seems to depend on the volume of water carried. Essentially 
young tributaries showijig no sign of having bt*en carved out of 
}-re-existing valleys are rari‘. Obviously these features accord with 
dutson’s history of tlie Jlarling Kauge rivers. 
No similar reconnaissance* of the H(‘U*na has l)een made, but 
from scattered ol)Servations we boUev(‘ that for a distance of 
about \‘2 miles above the Darlington Area the same features would 
be found. From detailed work at Gorrie ’s Farm, about 6 miles 
south of Ghidlow and 16 miles by river above Darlington Area, 
wo know that, in its ui^per reaches, the Hc'hma valley is mature. 
B. Physiography of the Darlington Area. 
In contrast to the Koleystone Area the Darlington Area includes 
the full width of the Helena Valley for three miles and lias 
several features of interest. 
1. HeJe/ia River . — The river enti'is the Area flowing in a W.S.W. 
direction through a steep-side<l valley with occasional broken water, 
but at its junction with Piesse Brook, which enters from the 
south, it turns to the N.W. and passes for more than a mile 
through a gorge-like valley, its grade still that of an immature 
stream. Shortly after emerging from tlie gorge it is joined from 
the N.E. by I^mith’s iSIill Brook, and from here to the western 
C(P*'e of the Area has tlie characters of a inatiu’e stream. Half 
a mile beyond Bniith’s ilill Brook junction it turns sharply to 
the W.S.W. again. 
Tribuiaries.^Thive types of tributary are distinguishable r 
(a) Wliolly immature tributaries— All but six of the many water- 
courses which enter the Helena iii the Darlington Area are of 
lliis type. They rise within the limits of the valley itself and 
ari' iiiseiiuent, owing their existence simply to the deepening au<i 
widening of the main vallev. Tlieir courses are jiretty evenly 
steep throughout, and Avaterfalls are rare; but oiviiig to the short- 
ness of their season of activity, they are unable to degrade as 
fast as the main stream, aiiil several steepen visibly as they iieai 
the Helena Diver. 
(!)) Rejuvenated trilmtarles— Smith’s Mill and Cohen Brooks and 
a stream which enters tlie Helena o])posite the mouth of Smith's 
