468 THE FRESH-WATER LOCHS OF SCOTLAND 
upper portion of this same consequent, of which the Duneaton and 
Douglas Waters were already subsequent tributaries. As the North 
Channel River and the Lower Clyde cut backwards through weak 
Carboniferous strata more rapidly than the tributaries of the Tweed 
among the durable Silurian rocks, they eventually captured the 
territory which had been temporarily annexed by the Tweed. 
A feature of special interest in connection with the topography 
of the Southern Block is the resuscitation of old palaeozoic land 
surfaces in the course of the development of the existing physical 
features. Thus we find evidence of the existence of a transverse 
valley system of pre-Upper Old Red Sandstone age, of which Lauder- 
dale is a characteristic example. In this ancient hollow, sediments 
of Upper Old Red Sandstone age were laid down which are now 
being eroded by the Leader Water. Another, but less obvious, valley 
is still buried under sandstones and conglomerates belonging to the 
same period, stretching across the Eastern Lammermuirs from Long- 
formacus to Dunbar. 
Nithsdale and Loch Ryan are instances of pre-Carboniferous 
hollows, for they are still floored in part by Carboniferous strata 
which are remnants of more extensive deposits. In the case of Loch 
Ryan, the Carboniferous rocks must have undergone considerable 
denudation before the deposition of the overlying red sandstones of 
Permian or Triassic age. Annandale furnishes striking evidence of 
a valley system dating back to palaeozoic time, as the breccias (Permian 
or Triassic) which floor the present valley near Moffat contain 
blocks of fossiliferous Lower Carboniferous strata that once filled 
these hollows. The hollow of Eskdalemuir is another example, for 
the deep staining of the Silurian rocks points to the removal by 
denudation of red strata from that area. Again, in the Abington 
region outlying patches of Carboniferous strata and breccia of 
Permian or Triassic age rest unconformably on the old Silurian floor 
in such a manner as to suggest that the Clyde took advantage of these 
weak sediments while cutting backwards as an obsequent stream. 
Along the western edge of the Upper Old Red Sandstone south of 
Melrose there are examples of a secondary system of smaller valleys 
following the grain of the Silurian rocks, which contain outliers of 
Upper Old Red Sandstone. Recent observations point to the 
existence of such sediments in the valley of the Ettrick far to the 
west of Selkirk. 
The relation of the Upper Old Red Sandstone to the Silurian 
rocks along the northern slope of the Moorfoot and Lammermuir 
Hills shows that part at least of the steep northern declivity was a 
feature established in Upper Old Red Sandstone time. Similar 
instances of the resuscitation of the old land surfaces along the north- 
