186 Tue Brack WATER oF DEE. 
Gap, three-quarters of a mile, and its length, nearly three 
miles, and the great resistance of these granite rocks, the 
Cooran Gap represents the largest, the deepest, the oldest, 
and the most elevated of all the Gaps in the Southern Up- 
lands. 
The other section at Craigencallie, further down the 
stream, is of a different nature, but equally emphatic. The 
eastern bank gives a relief of 2400 feet, and the western 
1800 feet, while the stream runs along the 7oo feet contour. 
This shows an excavation of 1700 feet of metamorphic rock 
—the hardest in Britain. 
There are at least four distinct types of windgaps due 
to the different forces at work in their formation—each type 
taking that distinct peculiarity of form characteristic of the 
producing agent. Authorities have already agreed that the 
windgaps at Biggar, at Cumnock, and at Carsphairn are 
stream cut. Not only so, but they are also agreed that these 
66 
three have been cut by a “* through ”’ or a consequent stream 
imposed upon the ridge. For want of a better name, may 
(a3 
we call them “‘ consequent ’’ gaps. 
The Gap at Cooran is of that same bold type—cut by a 
consequent. Indeed there is no alternative, no theory of 
downthrow or uplift, or fault could truthfully account for 
the phenomena of the Cooran. Undoubtedly that deep-walled 
Gap of the Dungeon, with its steep precipitous sides and its 
floor of treacherous morass, was the handiwork of the oldest 
and largest river crossing the Southern Uplands. 
The lower or Mossdale portion of the present Dee, from 
the Stroan to Parton Ferry, gives no valley, or plain, or gap 
corresponding in size or age to the Cooran excavation. Many 
ot the features of Mossdale area are post-Glacial, but even 
those that are admittedly pre-Glacial are of poor relief. They 
6¢ ”) 
are too ‘‘ young ’’ or ‘‘ immature ”’ to rank as contemporary 
with the ancient Cooran Gap. 
The Scree] Gap. 
There is another ridge of granite hills confronting these 
rivers in their south-easterly course. This range stretches 
from Criffel, westward, to Bengairn, near Kirkcudbright, and 
