EPISODE:
THE ORIGIN OF VALLEYS: "DILUVIALISTS" VS. "FLUVIALISTS"
"Many of these valleys and basins are drained by chasms and precipitous gorges of enormous depth; which could not have been produced by the most violent torrents that now flow through them, but must be referred to the disruption of mountain masses at the epoch of ancient revolutions that have overturned the globe" (Buckland 1820)
There was an active debate running through the first half of the 19thC. concerning the origin of valleys.
In the foreground of this Auvergne valley we can see that the river has cut a steep-sided, v-shaped valley through a "recent" flat-topped lava flow; but, the upper-reaches of the valley have a different, much wider form. Could the same river have accomplished both?
Massif Central, Auvergne region, France.
Puys de Sancy is at the head of the valley.
John Playfair (1748–1819), in his "Illustrations of the Huttonian theory of the Earth" (1802), argued the view of his late friend, the philosopher-geologist James Hutton, "that the rivers have, in general, hollowed out their valleys" (p.349): "Every river appears to consist of a main trunk, fed from a variety of branches, each running in a valley proportioned to its size, and all of them together forming a system of valleys, communicating with one another, and having such a nice adjustment of their declivities, that none of them join the principal valley, either on too high or too low a level; a circumstance that would be indefinitely improbable, if each of these valleys were not the work of the stream that flows in it" (p.114; "Playfair's Law"). On practical and methodological grounds, Playfair was severely critical of theories that invoked deluges for the formation of valleys, as well the transportation of drift and erratics and the creation of crags (p.377- 395; 395-406).
In 1810, Jean Andre de Luc (1727-1817) took issue with this view, stating that "the controversy concerning the origin of vallies, [is] the greatest which has arisen among geologists" (p.7). While he acknowledged that canyons and ravines were due to river action, de Luc then enumerated 16 reasons against the Hutton-Playfair view in general, and these were echoed through the next 30-40 years.
Certainly there were well-known characteristics of some valleys in NW Europe
that did not fit the Hutton-Playfair model, particularly in mountainous regions:
And in other regions:
Like English rivers such as the Cherwell and Evenlode, the Susquehanna at
Harrisburg, PA, cuts through rock structure:
geologists thought this was only possible if some watery catastrophe had cut the
valley though the structure.
(GoogleEarth snapshot)
In
1822, William Daniel Conybeare (1787-1857) and William Phillips
(1775-1828) argued that "to believe them [valleys in general] to have been
formed by their actual rivers, however long their action may have endured,
involves the most direct physical impossibilities. It is indeed the more
extraordinary that a cause so manifestly inadequate, should ever have been
embraced, since the fundamental fact of geology, namely, that the continents,
now dry land, were once covered with the ocean, which is of necessity (however
differently explained) common to every geological theory, involves in itself the
admission of a cause fully adequate: for, however that ocean may have been
brought to its present level, it could never (on any view of the matter) have
drained off the surface of the lands it has deserted, without experiencing
violent currents in its retreat; and in those currents (the existence of which
no one can on any hypothesis dispute) might have been found a force far more
commensurate to the effects to be accounted for" (p.xxiii).
In an 1823 review of William Buckland's "Reliquiae Diuvianae" ("Traces of the Flood") William H. Fitton (1780-1861) wrote that "The effects of water upon the solid strata of the globe have been the subject of much geological debate; but it is now almost universally admitted, that valleys have been excavated by causes no longer in action."
Later, in a 1829 study of the upper Thames, Conybeare characterized "the opposite theories of the fluvialist and diluvialist, the former ascribing such denudations exclusively to the operation of the streams actually existing, or rather to the drainage of the atmospherical waters falling on the districts, which it is supposed have become thus deeply furrowed by the gradual erosion of these waters, continued through a long and indefinite series of ages; the latter contending that such a cause is totally inadequate to the solution of the phenomena, and maintaining that they afford evidence of having been produced by violent diluvial currents" (p.145).
In 1828, Robert Bakewell (1768-1843), like de Luc in 1810, connected the question of valleys to the question of erratics: "There are few subjects on which the opinions of geologists have been more divided, than the formation of vallies. . . . Geologists seem now generally agreed, that the action of rivers is not sufficient to explain all the phenomena of vallies, and still less to account for the fragments of rocks scattered over extensive plains, at an immense distance from Alpine districts, where rocks similar to these fragments occur." Like Conybeare, he thought that valleys in general had been formed by rapid currents acting as the waters of the deluge, "or a succession of deluges," drained off the land: as when the tide goes out and we see "the water cutting out channels for its passage as it drains off" (he is quoting an analogy of Conybeare's). Bakewell also admired the "tsunami" theories of Hall and Pallas.
However, Bakewell did note one problem (p.476-477): "Granting the agency of a deluge, or a succession of deluges, there are still phenomena left, that their action will not satisfactorily explain. In the midland counties of England, for instance, there are beds of gravel, and fragments of rock, scattered over hills, that are not only far distant from the rocks which have supplied the fragments, but which are separated from them by deep vallies, over which it is supposed that the fragments could not have been carried, by any power of diluvian agency; for in England, we have not the glaciers to assist in their transportation. It has been imagined, that these fragments and beds of gravel were deposited in their present positions, before the intervening vallies were scooped out. But any subsequent deluge, sufficiently powerful to scoop out vallies, must also have swept away the loose stones on the surface. We must therefore admit, either that the water of the deluge covered the earth for some time, during which period the stones and gravel were deposited, and, on retiring rapidly, excavated the softer strata into vallies; or that a great change has since taken place in the level of particular situations, by elevation or subsidence."
Henry T. De La Beche (1796-1855),
also in 1829, likewise contrasted the “diluvialist” and “fluvialist” positions,
as Conybeare had termed the two camps: "Two opinions have been entertained by
geologists, as to the causes that have excavated valleys: some contending .that
they have been produced by the rivers that now run in them, aided by the
bursting of lakes and meteoric agents; while others consider that the greater
proportion of such valleys have been formed by what has been called diluvial
action, and by other causes operating at the bottom of ancient seas. It appears
to me that these two rival theories may be reconciled with the facts presented
by nature, and that both are, to a certain extent, correct. It seems to me that
aqueous excavations are of two kinds: 1. Those produced by vast and violent
causes not now in action; and, 2. Those resulting from the continuous and
gradual operation of lakes, rivers, and other agents that have been termed
meteoric: the latter series of causes operating upon valleys that most
frequently owe their prior existence to the former series, and both offering
very distinct appearances. Excavations of the second kind, or those produced by
actual streams, present cliffs, gorges, and ravines; while the first are marked
by grand and extensively rounded outlines, and by valleys of a breadth and
magnitude which would seem only referable to a voluminous mass of moving
waters."
De la Beche then lampooned the fluvialist view in the kind of satirical drawing for which he was well-known at the time:
"Cause and Effect: Bless the baby: what a walley he have a-made!"
Showing Frank Buckland (Buckland's son) creating a "piddling valley" (de la
Beche c.1829).
A "piddling river" and valley? (Glen Tilt, Scotland)
http://outdoors.webshots.com/photo/1031855827034361335shWgLeAgSA
QUESTIONS:
REFERENCES
Bakewell, R.1828 An introduction to geology. London Longman
http://www.google.com/books?id=hxqzgsrCUH4C&pg=PR1
Conybeare, W.D., Phillips, W. 1822 Outlines of the geology of England and Wales. London W. Phillips
http://www.google.com/books?id=p-8OAAAAQAAJ&pg=PP7
Conybeare, W.D. 1829 On the hydrographical basin of the Thames, with a view more especially to investigate the causes which have operated in the formation of the valleys of that river, and its tributary streams. Proceedings of the Geological Society of London no.12 p.145-149 http://books.google.com/books?id=PDPPAAAAMAAJ&pg=PA145
de la Beche, H.T. 1829 Notice on the Excavation of Valleys. The philosophical magazine and annals of philosophy October 1829 p.241-248
http://books.google.com/books?id=rkIwAAAAIAAJ&pg=PA241
de Luc, J.A. 1810 Geological travels vol.1. London Rivington http://www.google.com/books?id=se44AAAAMAAJ&pg=PP7
Fitton, W.H. 1823 Review of Buckland's Reliquiae Diuvianae Edinburgh Review v. 39 (1824) p.196-234 http://www.google.com/books?id=6jAbAAAAYAAJ&pg=PA196
Playfair, J. 1802 Illustrations of the Huttonian Theory of the Earth in, The Works of John Playfair, 1822 Edinburgh Archibald Constable & Co. http://books.google.com/books?id=MMkEAAAAYAAJ&pg=PP11