SECTIONAL TRANSACTIONS.—C. 375 
Prof. A. G. Ocitvie.—The mapping of erosion surfaces. 
Geologists and geographers are interested in denudation surfaces, though 
their respective view-points differ. For geographers it is essential that the 
character, extent and distribution of each surface be determined with 
reasonable accuracy. Investigation of surfaces in the field should therefore 
always be supplemented by construction of projected profiles by Barrel’s 
method as developed by D. W. Johnson, and, wherever possible, by erection 
of the rigid profiles properly spaced in plan. The time has come for 
serious attempts to map the remnants of separate erosion surfaces in 
Britain ; for this the reliable O.S. contours are an asset. Special difficulties 
occur due to the slight separation of surfaces where relief is low and also, 
as in parts of Scotland, where excessive dissection leaves only small rem- 
nants. Nevertheless the aim of all workers should be to produce regional 
maps of uniform type which may afterwards be correlated. AA Commission 
of the International Geographical Union has suggested a system of mapping 
and it has already made the correlation necessary to the production of a 
tentative map of erosion surfaces covering considerable areas of the 
European continent on the scale 1 : 500,000. 
A brief report was given of work, with D. L. Linton, aiming at the 
recognition and the mapping of surfaces in southern Scotland. 
Prof. H. H. Swrnnerton.—The denudation of the East Midlands. 
The loftiest surface in this area is situated on the southern extremity of 
the Pennines at a level of about 1,000 ft. This was for a long time regarded 
as a pre-Triassic surface which had been buried under the whole of the 
Mesozoic series. It has been shown that the members of this series, when 
traced westwards, tend to become thinner, and may never have reached the 
Pennines, whose surface may therefore have been always exposed. The 
existence of such superposed streams as the Dove and the Derwent, however, 
implies the former presence of at least a thin covering possibly of late 
Cretaceous rocks. Since that was removed this surface has been lowered 
continuously by denudation, a fact which raises the question, ‘ What, after 
all, are we trying to date?’ 
In the adjoining lowlands, on the south and east, there are several erosion 
levels. The highest of these is at about 650 ft. and is preserved as a fringe 
around the Pennines and in isolated fragments, such as that of Charnwood. 
The curves of equilibrium in the upper reaches of those valleys which 
incise the 1,000 ft. surface conform to this 650 ft. surface. Much of the 
lowland area is occupied by a very broad shallow valley feature produced 
in pre-glacial times by the Trent drainage system. The floor of this rises 
from 300 ft. near Nottingham to 450 ft. south of Ashbourne and in Need- 
wood Forest. The floor of this valley was dissected in mid-glacial times 
by the Trent and its tributaries, with the production of those flat-bottomed 
trench-like valleys which are so characteristic of the area. 
Mr. A. Austin MILLeErR.—Erosion surfaces in South Wales and South 
Ireland. 
The clearly marked erosion surfaces presented by the coastal plateaux of 
South Wales, from the mouth of the Wye westwards to St. David’s Head, 
occur at a variety of levels. ‘The most frequently occurring altitudes are 
200, 400 and 600 ft., but it is suggested that these plateaux constitute the 
dissected relicts of a once continuous plane of marine erosion and that the 
apparent breaks are due to cliffing of the emerged shore plane during the 
Progressive retreat of the sea. ‘The platform terminates in a degraded 
