Vice-President’s Address. 297 
Whether this represents a true Devonian Limestone in 
Scottish areas is, of course, open to question ; but whether 
it does or not is immaterial for our present purpose. I 
conceive that a downward phase of undulation slowly 
advancing northward, went on concurrently with the north- 
ward advance of the axis of upheaval that originated to the 
south. Eventually this axis of upheaval reached the area 
where the Lanarkian Rocks had been deposited, and then 
they, in their turn, underwent denudation as they were 
carried upward by the advancing wave, and the products 
of their denudation, in turn, supplied materials for the 
Caledonian Rocks, which were then in process of deposition 
farther north. The upheaval referred to must have been 
considerable, for the Lanarkian Rocks are very greatly 
disturbed and crumpled—all of which implies time; for I 
presume that no geologist is prepared to maintain that any 
disturbances sufficiently intense to throw rocks into the 
vertical position, or even to invert them, could well take 
place anywhere near what was the surface for the time 
being. After a considerable denudation, a downward phase 
of undulation, which had been slowly travelling northward, 
reached the spot where the Lanarkian Rocks now lay, and 
then they were covered by the conglomerates which lie at 
the base of the Caledonian Old Red in the Pentlands, and 
eventually by the great volcanic series itself. 
If the reader can conceive of a succession of such undula- 
tions travelling from the south northward, depressing one 
area after another in its progress from south to north, he 
will have little difficulty in realising the nature of the 
changes to which the various Old Reds, from the Lanarkian 
to the top of the Upper Old Red, are due. This view will 
explain how it happens that the Orcadian Rocks nearly, 
but not quite, pass upward conformably into the Upper Old 
Red; and, as Mr Peach has remarked, if we could trace the 
Orcadians perhaps only a short distance beyond the northern 
limit of the British Isles, we should probably be able to 
discover a perfect passage from these into the true Upper 
Old Red. 
In dealing with this part of the subject, therefore, I am 
