Tue Biack WaTER OF DEE. 183 
advent of the first Glacial stage represents a great stretch of 
time—according to Dr. W. J. Sollas, exceeding three millions 
of years. Allowing a lengthened period for the volcanic 
activities of the Eocene and Oligocene Ages, there still remains 
about two million years. Surely this was ample time for the 
rivers of Galloway to hallmark their hills with their irresistible 
flood plains imprinted in bold character and majestic outline, 
proclaiming the great message of continental evolution. 
Not only would these records of Tertiary river-work 
occupy a permanent place on this elevated tableland wholly 
beyond the obliteration of the Icework of a brief Glacial stage, 
but this topography must also be of an evolutionary nature 
—stage by stage—according to the laws of River Develop- 
ment laid down by W. M. Davies, I. C. Russell, H. Mac- 
kindar, and other authorities. 
Southern Upland Gaps. 
In dealing with the pre-Glacial river system of Central 
Scotland, H. M. Caddell in his Stor; of the Forth boldly 
carried the Argyleshire streams across Scotland into the 
Forth estuary. 
Dr. Gregory followed by establishing an older route for 
this Argyle-Clyde River through the Biggar gap into the 
Tweed valley. He also showed the predominating effects of 
pre-Glacial excavation to anything that could be produced 
in Glacial or post-Glacial times. Dr. Mort opened up a 
physiographic study with a paper on North Arran, describing 
in that island peneplains as a result of erosion. Later on, in 
his Rivers of South-West Scotland, he continues the plains 
and valleys through the Galloway gaps, dwelling particularly 
upon the source of the present Black Water of Dee. 
Thus it is evident that the plateau of the Southern 
Uplands was the testing ground of any older Scottish drainage 
system. And from the peculiar nature of the rocks along its 
valley floor the Black Water of Dee offered unique facilities 
for the study of uplifts and of river captures. 
The Cooran Dee. 
This Galloway Dee rises between the wild crags of 
Craignaw and Dungeon on the western bank and the Kells 
