The North
Downs subaerial denudation controversy of the
1860s
In the 1860s the generally
held view amongst geologists was that the
escarpments of the North and South Downs were
ancient sea cliffs, and that much of the low-lying
area of the Weald had been eroded away by marine
action.
Our distinguished former
member William Whitaker who, along with others,
had made a detailed examination of the ground
came to a different conclusion, and read a
paper entitled 'On subaerial denudation, and
on cliffs and escarpments of the Chalk and the
Lower Tertiary beds' before the Geological
Society of London on 3rd May 1867. To its shame,
that Society declined to publish the paper in
full, only an abstract (under an incorrect title)
appearing (Proceedings of the Geological
Society of London, 23, page 265.)
Whitaker's paper was,
however, published in full in the Geological
Magazine, the editors in fact arranging with
the author to produce 'a large number of
copies … so as to distribute them
amongst the Fellows of the Society.'
Whitaker was, of course,
right! Marine erosion had nothing at all to
do with the creation of the escarpments. His
arguments were summed-up concisely in the form
of a comparative table (see below):
| Table: Comparison of
the distinctive features of escarpments and
cliffs |
| Escarpments
| Cliffs
|
| (a) Run along the strike, or
in other words, keep to one formation throughout
| (a) Rarely run
along the strike, but at all angles to it, and cut through
many formations in succession |
| (b) Tops more or less even and often nearly flat
| (b) Tops mostly very uneven |
| (c) Form the highest ground of a country, overlooking other parts
| (c) Rarely through the highest ground of a country, but mostly backed by higher ground |
| (d) Very rarely have the sea at their foot, but often springs and watercourses
| (d) Sea at their foot |
| (e) Often run in more or less winding lines, though in general direction following the strike
| (e) Run nearly straight, or in curves of very large radius, when through homogeneous rock, and when not broken through by valleys |
| (f) No beach at their foot
| (f) Often a beach at their foot |
| (g) Are now being destroyed by the sea in places where the sea touches them
| (g) Are now being made by the sea (aided by atmospheric actions) |
| (h) Bases rise towards the watershed and have nothing to do with sea-level
| (h) Bases at the sea level, or very near it |
| (i) Those of successive formations run in more or less parallel ridges for long distances, with plains, vales, or valleys between
| (i) No such parallel arrangement known, long fringes of land divided by belts of sea not being common, except in such cases as Coral Islands, where the features have been caused by growth, not by decay |
| (j) Valleys and combes are not abruptly cut off by them
| (j) Small valleys and combes are often abruptly cut off by them |
| (k) Beyond them the ground soon rises above their bases
| (k) Beyond them the ground falls below their bases (beneath the sea) |
| (l) The waterslopes of valleys that breach them fall inwards from them (rising outwards of course)
| (l) The waterslopes of valleys that breach them rise inwards from them |
| (m) Rivers and valleys have their heads at or near them. Water flows away from them at last
| (m) Rivers and valleys end at them. Water floes to them at the end |
Next time you are
walking along the North Downs or the Seven
Sisters, or at the Mole gap or Cuckmere
Haven, pause and admire Whitaker's triumph
over the 'must-have' school of geologists
of his day!
Paul W Sowan
|