active tributary worked its way back at
its head into the basin of one of the cross-streams, and drew off into
its own system the head-waters of this other stream. With this new
flood of water the strengthened system still further deepened its
original ravine across the strike, while the beheaded cross-stream or
streams rapidly dwindled in importance. Ultimately, the tributaries of
the surviving river-systems appeared as the most important feature,
stretching far west--in the case of county Cork--along the synclinal
hollows; while the original cross-ravine remained in the course of
each river, a right-angled bend occurring thus in the lower portion of
the valleys. Jukes urged that the upper part of the original
cross-ravine can be traced above the bend in each case, though the
stream now descending along it seems merely a tributary entering
parallel with the north-and-south portion of the main stream.
Moreover, the tributaries on the north side of the great synclinal
valleys may in many cases be the relics of original cross-streams that
once flowed directly to the sea until captured by the growth along the
synclinal of the tributary of another stream. The Blackwater, rising
on Upper Carboniferous beds on the Kerry border, thus falls steeply
southward to Rathmore, and then turns eastward along the synclinal
valley of limestone from Millstreet to Cappoquin. Here it abruptly
turns south, keeping, in fact, to that part of its valley which was
first developed. The Lee, rising in the Old Red Sandstone moors of
Gouganebarra, runs east, encountering one or two patches of limestone
in the floor of the synclinal on its way, mere residues of the rock
that once occupied the hollow. Near Cork, the limestone and
accompanying shale are better preserved; but the river, instead of
continuing along the synclinal through Middleton to Youghal, turns
south, and forms the now submerged valley of Cork Harbour.
Observations have shown that the coast lay much at its present level
in pre-Glacial times, and that Cork Harbour was thus a marine inlet
before the ice descended into it. The synclinal valleys of Bantry Bay
and Dunmanus Bay were also, in all probability, submerged at this same
early epoch.

The county has been famous for its copper-mines, notably at Allihies
in the extreme west. The region south-west of Bantry has been mined in
several places. Both gold and silver h