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Cadernos Lab. Xeolóxico de Laxe ISSN: 0213-4497 Coruña. 2001. Vol. 26, pp. 101-120

Reflections on the fate of some geomorphological ideas Reflexiones sobre el destino de algunas ideas geomorfológicas

TWIDALE, C. R.

AB S T R A C T

In , as in other sciences, investigation is concerned with the collection and characterisation of data, and the generation and testing of working hypotheses. Considering the analysis of landforms and landscapes, the reasons some explanations have been accepted, others rejected, and yet others refuted but later approved, are exa- mined. In particular, why hypotheses which were considered plausible but were shown to be flawed still received general acclaim, whereas others of obvious merit were igno- red, are discussed. The roles of chance and the human factor are also broached.

Key words: acceptance/rejection of ideas; plausibility; human factor; fashion in geomor- phology; concepts considered: age of landscape, Channeled Scabland, dunes, inso- lation weathering, lunettes, river velocity, sheet structure, submarine canyons Department of Geology and Geophysics, University of Adelaide, Adelaide, South Australia 5005. Tel: Direct (08) 8303 5392, Department (08) 8303 5376, Fax: Department (08) 8303 4347, E-mail: rtwida- [email protected] 102 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001)

INTRODUCTION Earth is roughly spheroidal, but who, using this as a basis, had worked out how Einstein once stated that it is not inte- to measure the size of the planet on which llect but character which makes a great we live. scientist. Certainly, high intelligence is no The ever changing interpretation of guarantee of moral worth, whereas tena- various landscape elements well illustrates city, integrity and moral courage are cha- POPPER’s (e.g. 1963) assertion that no racteristic of much of the best scientific scientific theory may ever be regarded as research. Parga Pondal, whom we honour proven, if only because, as CRICK (1988) with this volume, displayed such qualities has pointed out, any theory which fits all not only in his geological career but also the facts must be flawed because some of in the much more dangerous arena of life. those facts will prove to be misleading. In research it is frequently necessary to Also as Kant pointed out two centuries persist with an idea in the face of ridicule, ago, truth is reality as perceived by human obloquy and professional ostracism. One eyes and interpreted by human minds; and may eventually be shown to be in error in the interpetation of data, especially field whole or in part, but once convinced of an data, is a personal matter, varying with interpretation it is obligatory to defend it the observer’s character, training and expe- vigorously but professionally, tenaciously rience (READ, 1957, p. i). But not all but not stubbornly, and always with an rational hypotheses find ready acceptance, open mind. Yet to win acceptance for an and the more radical or unconventional idea is not always easy and not always the idea the more difficult it has proved to based in logic. Contemplating interpreta- have it aired. Yet other concepts, clearly tions of landscape of bygone ages one is questionable, immediately receive the sta- adversely surprised by the persistence of tus of a theory. What factors influence the untenable ideas, yet also pleased with the reception accorded an interpretation or certain knowledge that there have always concept perceived to be new? been rational beings. Thus, on the one hand, despite the incontrovertible eviden- ce to the contrary, including pictures from RATIONAL BUT FLAWED space, there are still those who believe in a Many hypotheses and assertions were flat Earth. Again, there are those, a few, plausible in light of the known data at the who, genuinely believe the biblical time they were derived, but were overta- account of the age of the Earth, who, des- ken by new data and either modified or pite all the evidence, regard reports of abandoned. Moon landings as propaganda lies, while complacently accepting biblical allegories as literal truths. On the other hand, two Plausible but placed in perspective millenia or so ago, in classical Greek and Insolation has long been cited as a Roman times, there were those who not cause of rock disintegration. In ancient only argued from observations that the India and Egypt, the expansion of rock CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 103 consequent on heating was used as an aid disintegration and spalling in the labora- in quarrying. The rock surface was cleared tory have failed, possibly because the time of soil and other overburden and a bonfire factor cannot be reproduced, though also lit on the bare rock surface. The heat of because the experiments were carried out the fire caused the near surface rock to in dry conditions (see GRIGGS, 1936). expand and arch, making it easier to break The critical observations placing insola- the mass into manageable blocks (e.g. tion in perspective are due to BARTON WARTH, 1895). The heat of bushfires (1916). and that generated in nuclear explosions Barton visited some of the pharaonic also causes rocks to flake (e.g. WATANA- monuments in Egypt. Some had fallen on BE et al., 1954). Little wonder that rock to the desert sands, others into the silts of weathering has been attributed to heating the Nile . In both situations, Barton and cooling. noted that the upper faces of blocks and Two arguments have been put. First, columns, which when used to construct many rocks (e.g. granite) consist of mine- the various temples, etc. had been freshly rals of different composition and colour, quarried and which had been exposed to which absorb radiation differentially and the Sun’s radiation for 3-4000 years, sho- therefore heat and expand at different wed no detectable sign of disintegration rates. At night or in winter they cool. or decay. On the undersides, on which dew After many alternations of such heating had formed from time to time, on the and cooling, diurnal and seasonal, the rock blocks buried in desert sand, and espe- breaks down into fragments: granular cially those buried in flood plain silt, there disintegration. Second, rocks are poor con- was clear evidence of alteration. ductors of heat, so that while rock at and Such observations do not imply that near the surface heats and expands, that insolation does not take place, but they just below does not, with the result that show that it acts much more slowly than eventually the surface layer splits away: does moisture attack, even in flaking or spalling, depending on scale, where insolational heating is maximal and and more generally, 'exfoliation'. moisture is scarce. Common rock-forming Such reasoning is convincing, and fla- minerals readily react with moisture and kes and slabs of rock as thick as those in the humid tropics, where the prevalent involved in A-tents or pop-ups, and even humidity and high temperatures are con- those referred to as sheet structure, have ducive to chemical activity, alteration been attributed to insolation (e.g. SHA- takes place very quickly. CAILLÈRE & LER, 1869; MacMAHON, 1893; SCOTT, HENIN (1950) have shown that in 1897, p. 225; PIRSSON & SCHU- Madagascar, mica in a newly quarried CHERT, 1915, p. 20; TYRRELL, 1928). crystalline rock shows signs of decay Yet, at best, such insolational weathering within a few years, and examination of a is of minor importance in nature. The heat granite quarried and used in a building in generated in fires and explosions is short- Rio de Janeiro again revealed evidence of lived and localised. Attempts to simulate alteration within a decade or so. Feldspars 104 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001) in dated volcanic ash and lava are altered with the observational evidence of rushing in 103 years in the humid tropics, a soil a headwater streams in the mountains and metre thick has been shown to develop on apparently sluggish meandering rivers on a dacite in about 5000 years, and ferro- the plains. Explanations of many river magnesian minerals, especially, decay very characteristics and associated landforms rapidly in such conditions (e.g. WEYL, were based in this concept of downstream 1954; HAY, 1960; TRESCASES, 1975) decrease in velocity. For example, the and detectable rapid rates of weathering deposition of debris in flood plains was are evidenced elsewhere (e.g. BIRKE- said to be due to low velocity rivers not LAND, 1974; THOMAS, 1994). Though having the energy to transport the availa- the Nile is an exoreic stream flowing ble load. The absence of coarse detritus in through an arid region, in the flood plain plains sectors of major rivers like the the combination of moisture and heat in Congo and Amazon was attributed to some measure simulate the humid tropics. there being insufficient energy to carry Barton's simple but astute observations blocks and boulders. placed insolational weathering in perspec- Velocity is taken as the maximum flow tive. developed (and demonstrated by measure- ments) in the deepest part of the channel, Plausible but incorrect and about one third of the way down bet- ween the water surface and stream bed. River velocity provides a splendid There are, as expected, local departures example of an apparently logical explana- from this generalisation, as for example on tion that has perforce been abandoned. river curves where velocity is greater on Though, thanks to the efforts of HUT- the outside than on the inside of the bend, TON (1788, 1795) and GREENWOOD and where the river passes through a defi- (1859) it was recognised early in the his- le or narrows. The discharge or volume of tory of geomorphology that the vast majo- a stream (Q) is a function of cross section rity of valleys have been eroded by the area of channel (A) and velocity (V): Q=A rivers that flow in them, other early ideas x V. Water cannot be compressed so that a of river activity and their consequences narrowing of channels is accompanied by were logical, but in error. an increase in velocity; and vice versa. But Surveys show that the longitudinal such variations are local and the overall profiles of rivers most commonly describe picture stands. concave-upward courses. Gradients are The concept of downstream decrease in steepest in the headwater reaches, and river velocity was based in reasonable become increasingly gentle as the sea is deduction. But it stood only until the approached. It was not unreasonably assu- later '50s when the results of measure- med that velocity would be greater on ste- ments of stream velocities became known. eper than on gentle slopes, and it was con- Stream gauges were set up at intervals cluded that, overall, velocity would decre- along various rivers and recordings conti- ase from source to sea. This is consistent nued over considerable periods. Contrary CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 105 to expectations, apart from a short sector a crude dam behind which sediment is in the headwater region, river velocity trapped and the channel aggraded.] increases downstream (LEOPOLD, 1953). It says much for the ingenuity of geo- But how can a river flow more rapidly on morphologists that the same features that gentler than on steeper gradients? The were explained in terms of downstream explanation appears to involve channel diminution of flow are just as plausibly characteristics, and in particular the ratio interpreted within the new framework of of cross-section area to wetted perimeter. stream activity. Many flood plains, it is In the headwater reaches of a stream, the now realised, are the result of point channel is eroded in bedrock, with many deposition during lateral planation by irregularities, and many cobbles, blocks rivers (see e.g. WOLMAN & LEOPOLD, and boulders resting on the stream bed. 1957; LEOPOLD et al., 1964) and the Thus the wetted perimeter, or length of character of load in plains streams reflects rock surface in contact with water, is long the weathering and attrition of debris and in relation to the cross-section area of the the consequent non-availability or supply channel. Downstream, however, on the of coarse fragments. Such intellectual agi- plains, the discharge is higher and the lity also highlights the fact that Earth cross-section area greater; moreover the scientists in general, and geomorpholo- river channel is in some measure at least, gists in particular, are good at explaining eroded in alluvium, with few irregulari- what has happened, but not so impressive ties. Thus the ratio of wetted perimeter to when endeavouring to predict events. cross-section area is low. As some 95% of the potential kinetic energy of rivers is Plausible but questionable dissipated in frictional losses at the con- tact of flowing water with bed and banks Some interpretations are plausible but (RUBEY, 1952), there is a much greater owe something to the reputation or dis- loss of energy in the headwaters than in tinction of the proposer, as well as to its the plains sectors. Moreover, in rocky inherent qualities. The offloading hypo- mountain channels a great deal of energy thesis of sheet fractures provides such an is lost as a result of turbulence and eddies example. Arcuate fractures are characteris- caused by obstacles and irregularities. tic of massive rocks such as granite, and [Incidentally, such frictional loss of have long been noted in the literature. energy is the basis of a method, derived Though some early writers (e.g. not from hydraulic theory but from trial MERRILL, 1897; DALE, 1923; BAIN, and error, commonly used by farmers to 1931) attributed them to torsional and impede or repair gully erosion. Dumping compressional stresses, they have for many many large blocks and boulders in the years been interpreted as due to offloading channel, first, increases the wetted peri- or pressure release consequent on erosional meter and thus reduces stream energy and unloading; so much so that in text books velocity, and, second, provides the basis of of geology and geomorphology, as well as in research papers, they are commonly 106 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001) referred to as offloading or pressure relea- and can best be explained in terms of a se joints, or some similar term. The theory compressive environment (VIDAL behind this nomenclature is due to GIL- ROMANI et al., 1995; TWIDALE et al., BERT (1904) and is compelling. 1996). For example, at several sites sheet Imagine a mass of granite exposed at fractures describe synforms within domi- the surface. That it is exposed implies the cal hills, a relationship impossible of erosion of several kilometres of superin- explanation by offloading. Sheet fractures cumbent rocks, for granite is emplaced are typical of bornhardts or domical hills, deep in the crust in an environment cha- many of which are lithologically identical racterised by high ambient temperatures with the rock beneath the surrounding and lithostatic (hydrostatic) pressures. plains, and which appear to be developed The granite cooled at depth through heat in rock characterised by low fracture den- loss to the surrounding rock, but as the sity, presumably as a result of compressive overlying crust thinned through erosion, stress. The development of fracture sets pressures diminished and the rock tended parallel to recently formed surfaces can be to expand radially, normal with the coo- understood in terms of realignment of ling surface, i.e. essentially the land surfa- compressive strain in parallel to the chan- ce. Many rock masses tend to be rounded ging geometry of the land surface. by weathering, and particularly by mois- Fractures analogous to sheet fractures can ture attack in the subsurface. It was pro- be produced experimentally by squeezing posed that expansive or tensional radial partly confined blocks (HOLZHAUSEN, stresses would be manifested in sets of 1989). And so on - there is much eviden- fractures disposed tangential to the stres- ce to support the suggestion that sheeting ses and parallel to the land surface, and is associated with compression, and much that these are the well-known offloading field evidence incompatible with the pres- joints. So persuasive is this explanation sure release hypothesis. Gilbert himself that other possible interpretations of the recognised that sheeting in the eastern fractures are pre-empted by their being United States was possibly related to com- widely referred to as offloading joints, etc. pressive environments (DALE, 1923, p. That sets of sheeting fractures in some 29). places parallel recently eroded surfaces, [Yet when as a young man in the mid such as cirque headwalls and valley side '60s and visiting a university not far from slopes, is cited as evidence of rupture due Dartmoor, I suggested to my host profes- to erosional offloading (e.g. LEWIS, 1954; sor that I thought the sheet structures I KIERSCH, 1964). had observed on nearby granite massifs Whether joints or faults, all fractures could not satisfactorily be explained in are a manifestation of pressure release in terms of erosional offloading, I was ridicu- the sense that they presumably disappear led: 'What on earth are you thinking of - in depth as a result of high lithostatic of course offloading joints are due to offlo- pressures, but much evidence and argu- ading!'; and referees reviewing (and ment is inconsistent with pressure release, recommending rejection of) a paper pre- CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 107 senting a similar conclusion in the early This theme of constant change finds clear '90s offered the same circular argument.] expression in the various models of lands- cape evolution applied to the analysis of MENTAL BARRIERS landscape. W.M. Davis, for example, is well Some rational explanations based in known for his concept of the geographical field evidence have not been accepted (or, more properly, the geomorphological) because of an inability or refusal to accept cycle, concerned with the evolution of the magnitude of natural forces and the landscapes through time and with the infinite immensity of time. development of the peneplain (DAVIS, 1899). According to Davis, rivers and An Ussherian view of landforms: the streams in the form of wash and rills antiquity of landforms extend to every last part of the land surfa- ce: Consider for example the question of 'a river is ... a moving mixture of water palaeosurfaces. James Hutton lived two and waste in variable proportions, but mostly centuries ago and he is widely regarded as water; ... one may fairly extend the "river" over the father of modern geology. It has been all its basin and up to its very divides. said that he '... discovered time' (EISE- Ordinarily treated, the river is like the veins of LEY, 1961 p. 65). Amongst his many a leaf; broadly viewed it is like the entire leaf.' astute and penetrating visions of the Earth (DAVIS, 1909, p. 267) was the grand design whereby the des- The implication is that the entire land truction of old landscapes provided the surface undergoes constant change, ero- materials for the construction of the new. sion on hills and higher plains, and as a He saw this recycling process as having corollary, deposition in valleys; but all is operated in all past and future time, and changed in some degree or other, and no he concluded with the famous assertion landscape can long survive attack by that he could see in the landscape no ves- external agencies. Other models of lands- tige of a beginning and no prospect of an cape evolution, such as scarp retreat end (HUTTON, 1788, 1795). Another of (KING, 1942), or steady state develop- Hutton's great themes revolved around ment (HACK & GOODLETT, 1960; the constant wearing away of the land sur- HACK, 1960), both of which are applica- face, and many later workers, either tacitly ble in particular structural settings, or explicitly, made the same point, with carried the same inbuilt age limitation. the implication that the Earth’s surface is Even in favourable circumstances no surfa- mostly very young, and with the excep- ce ought in geologic or stratigraphic tion of exhumed forms, nowhere older terms to be older than Oligocene, i.e. no than Te r t i a r y, i.e. nowhere more than more than some 30-35 millions of years about 60 millions of years old (WOOL- old (see TWIDALE, 1976). DRIDGE, 1951, p. 23; LINTON, 1957; Yet for the past 70 years various inves- THORNBURY, 1954; BROWN, 1980). tigators have been driven by stratigraphic 108 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001) and topographic evidence to the conclu- H O RTON, 1945; TWIDALE, 1976). sion that facets of the contemporary lands- Certainly, and contrary to the Davisian cape date back 70-100 million years or teaching cited earlier, by the mid 'thirties more, to the later Mesozoic (HOSSFELD, there were suspicions that erosion was not 1926; CRAFT, 1932; HILLS, 1934). everywhere equally distributed over the Subsequent work has substantiated the land surface. Concerned to explain the sur- suggestions of these pioneer workers, vival of bevels high in the Appalachian though the extent of old palaeosurfaces topography, KNOPF (1924, p. 637) des- and the certainty attaching to their great cribed some high level remnants as 'out of ages has been made possible, on the one reach of erosion', implying that erosion, in hand by advances in regional stratigraphy this instance by rivers and streams, was and on the other by radiometric dating. not ubiquitous even at the local scale. For example, the summit surface of the That divides are relatively immune to ero- Gawler Ranges is an Early Cretaceous fea- sion find support in HORTON's (1945) ture (some 120-130 millions of years old; concept of a headwater zone of nil erosion. CAMPBELL & TWIDALE, 1991). That Meanwhile, however, Knopf’s implication of the Hamersley Ranges is of Eocene age of unequal activity had been taken up and and at least 60 millions of years old, the developed by CRICKMAY (1932, 1976) ribbed crestal bevel of Ayers Rock is at and later by TWIDALE (1991). The con- least Maastrichtian in age, and Kakadu cept of unequal activity focuses on the (Arnhem Land) and the Arcoona Plateau ubiquity and effectiveness of water as an were in existence in the Early Cretaceous agent of weathering, and on rivers as rein- (TWIDALE, 1994). The ancestors of forcement or positive feedback systems. If, many modern rivers can be traced back far for whatever reasons, rivers erode their into geological history, in some instances channels but there is little or no lowering at least 120 million years and in others a of divides, then the interfluves will be pre- mere 60 million (TWIDALE, 1997). served, particularly if the scarps defining Remnants of ancient landscapes are pre- the uplands are also essentially stable. served in other parts of the world (e.g. It might be thought that the advent of KING, 1942, 1950; MICHEL, 1978; physical or numerical dating might resol- D E M A N G E O T, 1978; BRICEÑO & ve such difficulties: not at all. A dramatic SCHUBERT, 1990; TWIDALE & VIDAL example concerns the revision due to ROMANI, 1994; TWIDALE, 1994). radiometric dating of the landscapes of Hutton’s concept of constant change and Kangaroo Island, in South Australia. Davis' of ubiquitous erosion are not uni- SPRIGG et al. (1954) established that the versally applicable. lateritised surface predated basalts extru- Concurrently with the great age of ded near the present northeast coast. At some landscape elements being establis- the time they worked there were few hed, circumstances conducive to their per- radiometric dates, and they reasonably lin- sistence were also noted (e.g. KNOPF, ked the basalts to the stratigraphically 1924; CRICKMAY, 1932, 1974, 1976; dated later Cainozoic volcanicity of the Mt CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 109

Gambier area and adjacent parts of wes- The concept of constant and widespread tern Victoria. In these terms the laterite change was, after all based in observations, predated the , which appeared reasonable perceptions and common sense: consistent with stratigraphically dated how could a landscape constantly subjec- laterites in northern Australia. The strati- ted to the elements not be worn down? graphic relationship is correct, but the Rational arguments were, however under- temporal placement of the chronology was mined by the development of a different drastically changed with the discovery way of viewing processes and landscape, that the basalt is Middle Jurassic, not though these new ideas were not given Quaternary, in age (WELLMAN, 1971). serious consideration for many years. On In these terms the laterite still predates the contrary, both Crickmay and his con- the basalt, but is younger than the cept of unequal activity, were subjected to Permian glacigene rocks on which it is in ridicule (TWIDALE, 1993). places developed. Regional stratigraphic considerations suggest a Triassic age for Quantification to the rescue the duricrust and the surface on which it developed (DAILY et al., 1974). Antiquity The forces of Nature are commonly of this order is confirmed by oxygen isoto- underestimated. In geomorphology, the pe analysis of clays from the lateritic pro- impacts of some events on the landscape files (BIRD & CHIVAS, 1988, 1993). were either not recognised or not believed [When an attempt was made to because the investigators could not - or publish this evidence, argument and con- would not - accept the implied magnitu- clusion (DAILY et al., 1974) it was rejec- de of the forces at work. The importance ted by the first journal to which the of floods in shaping the landscape was manuscript was submitted, one referee recognised early, but the possible magni- uncompromisingly stating that the con- tude of natural floods was not. Quantified clusion was 'impossible'. However incre- relationships were established between dible it may have seemed at the time, the stream discharge and velocity on the one conclusion was surely worthy of an airing hand, and such features as channel width, and eventually more liberal views prevai- meander geometry and depositional featu- led. Unfortunately, institutional disbelief res such as bars and ripples, on the other resulted in many official maps carrying (e.g. TRICART, 1961; LEOPOLD et al., legends which indicate laterites at least 1964; MALDE, 1968). Only then did the 150 million years too young and based in origin and significance of certain natu- a tectonically unlikely concept for another rally-occurring riverine forms become 20 years or so.] comprehensible. The impacts of very large The survival of land surfaces for some if localised floods, either natural (e.g. hundreds of millions of years was and still BAKER et al., 1988; GARCIA RUIZ et is regarded by many as unreasonable or al., 1996) or associated with burst dams impossible (e.g. BOURMAN, 1989, p. (e.g. TRICART, 1960; KIERSCH, 1964) 47, 1995, p. 16, to take a recent example). reinforced these conclusions. 110 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001)

Even so, while the impacts of the lar- probably in a few hours, during catastro- gest floods did not defy comprehension, phic flooding due to the breaking of the their implied magnitude was so enormous glacial barrier which retained Lake as to be unacceptable. The basaltic Missoula. of eastern , [Bretz’s initial interpretation of the in the northwestern U.S.A., is occupied by Channeled Scabland was correct but it the Channeled Scablands, a region charac- met with strong institutional resistance terised by interlaced broad channels, inte- (see e.g. BAKER, 1978) and it was not rrupted by gigantic , with enor- until 50 years later, when the processes mous bars and ripples in the channel flo- had been quantified and a source of the ors and huge blocks of country rock huge volumes of floodwaters belatedly strewn over the landscape. Various expla- recognised, that it was accepted. nations have been offered for this stupen- Fortunately Bretz lived long enough to see dous landscape (BAKER, 1973). Suffice it his explanation vindicated. A combina- to say that BRETZ (1923, 1933; BRETZ tion of quantified processes and stratigra- et al., 1956) attributed all the recent ero- phic knowledge convinced the scientific sional and depositional features to a single world.] catastrophic flood, but this was questio- ned and alternatives suggested, because a CONVERGENCE source for the implied huge quantities of water was not identified; notwithstanding An untenable idea or explanation is that PARDEE (1910) had earlier descri- one that is widely considered not to be bed evidence of the -dammed 'Lake supported by the available evidence. But Missoula'. This was the huge body of just as truth is rarely pure and never sim- water which was released on the melting ple, so Nature is commonly complex, and of the ice barrier (see also BAKER, 1995). it is not unusual for similar forms to evol- The earlier systematic work relating the ve in different ways - they are said to be size of dunes, ripples, transported blocks convergent. and channels to stream discharge allowed the volumes of water involved in the sha- Blinkered vision ping of the Channeled Scablands to be computed (BAKER, 1973). They are an Submarine canyons are huge chasms order of magnitude greater than even the which resemble terrestrial gorges and highest floods recorded on modern rivers. score the continental slope and shelf in all The erosion of immense channels and parts of the world. Some are more than a waterfalls, the deposition of huge bars and kilometre deep. They have been known for ripples, the transport and deposition of many years, and various explanations have the huge blocks of basalt, are commensu- been offered for them. For example, SHE- rate with the huge discharges implied. PARD (1948) argued that they are terres- The reshaping of the Scabland topography trial gorges that have been drowned, but was accomplished about 14,000 years ago, this suggestion is at odds with the eviden- CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 111 ce and has, rightly, been rejected as a ples of a particular landform which have general explanation. The weight of evi- proved to be genetically atypical: their dence supports the suggestion that they observations and reasoning were sound, are due to turbidity currents, huge sub- but were applied to what were proved to marine rivers of sediment carrying water be unusual examples. (DALY, 1934; KUENEN, 1950; HEE- ZEN & EWING, 1952; HEEZEN, The wrong place 1956). But there are exceptions. Some 6 Lunettes are small crescentic fixed million years ago, during the later dunes located on the lee sides of lakes and Pliocene, what is now the Mediterranean lake beds. Though similar forms had been Sea was a deep trough occupied by a desert earlier recorded from Texas (e.g. COFFEY, (HSÜ, 1972). Rivers draining northward 1909), HILLS (1940a) described and from what is now Libya poured over the named lunettes from northwestern edge of the African continent and eroded Victoria. Some bordering Lake Eyre, in huge chasms, which were drowned and central Australia, are up to 50 m high converted to submarine canyons when the (DULHUNTY, 1983), though most stand Straits of Gibraltar were breached and the of the order of 10 m above the level of the sea flooded the basin. They are typical adjacent lake depression and plains. Hills Shepardian canyons, and Hsü records that attributed the fine-grained lunettes with a terrestrial origin was suggested for the which he was concerned to atmospheric Libyan features, but the interpretation was dust being moistened, coagulated and rejected as untenable and the paper never deposited on passing over the lake: what published because of the widespread gene- became known as the 'wet' theory. A few ral evidence favouring turbidity currents. years later this explanation was challenged The fact that near its mouth the Nile had by STEPHENS & CROCKER (1946) who excavated a gorge at least 300 m (and pointed out, amongst other things, that maybe as much as 1500 m) deep in rela- many lunettes are built of sand, which tion to the same low baselevel provided by could not have been transported in sus- the desiccated Mediteranean basin, was pension. They argued that wind action on ignored by referees and editors, as was the bare dry alluvial flats in internal drainage possibility of convergent evolution or basins would cause both the scouring of e q u i f i n a l i t y. The probable truth was lake basins and the transport of debris to denied. the edge of the basin where it would be trapped by vegetation: the so called 'dry' CHANCE theory. BOWLER (1968) reported gra- velly debris from within lunettes, which Chance has been described as a nickna- he considered to be relic Late me for providence. If so, providence has forms, and in the same year CAMPBELL been unkind to some investigators who (1968) reported similarities in mineralogy had the misfortune to investigate exam- and texture between lake bed deposits and 112 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001) adjacent lunettes, and the presence of Correct but atypical rudimentary cross-bedding. She also poin- ted out that in terms of the dry theory, The structure of desert dunes of central lunettes ought to be located on the lee Australia provides another example of sides of basins in respect of summer or dry unlucky choice of investigation site. season winds whereas many are oriented MADIGAN (e.g. 1936, 1946) described with respect to wet season winds. It was the longitudinal dunes of the Simpson also difficult to understand how the mate- Desert, central Australia, as mobile cons- rial constituting sandy or silty lunettes tructional forms shaped by the wind. bordering salinas could have been eroded When, however, Donald KING (1956, by the wind from a source area covered by 1960) investigated dunes adjacent to Lake a layer of salt. To accommodate this and Eyre he found they consisted of a veneer of other field evidence, she proposed that sand over an elongate ridge eroded in lunettes are comparable to coastal foredu- lacustrine strata: they were not depositio- nes. In the wet season waves (even in the nal forms but stationary wind-rift dunes. shallow water implied by the topography King's data were accurate, and his reaso- of the basins) carry sediment to the lee ning impeccable, but he extrapolated his shore where it is deposited in beaches and findings not only to the entire Simpson whence it is carried by the wind a short Desert dunefield but to all the Australian distance and trapped by vegetation, for- dune deserts. In this he was wrong, for ming the mounds known as lunettes. [She bulldozed sections of numerous dunes later found that the essential evidence for later showed beyond doubt that they are this mechanism had been noted about a built of sand, and that they have been century previously by WOODS (1863, p. constructed by the wind (e.g. WOPFNER 28-29)!] & TWIDALE, 1967). King's error was to While these investigations were in extrapolate without checking, which is an hand, Hills defended the wet theory with obvious thing to do, but is in some cir- some vigour, but faced with the evidence cumstances - like those in which King and arguments graciously gave way and found himself - logistically difficult to acknowledged that the material of which accomplish. lunettes are constructed derived from the lake basins and also attributed their trans- THE HUMAN FACTOR port to saltation (HILLS, 1975, p. 147). Had Hills not chanced to work on what it Human traits impinge on the question transpired were rather atypical silty lunet- of scientific discovery in various ways. The tes in northwestern Victoria, he would, ingenuity of the human mind has provi- almost certainly, have reached different ded inestimable benefits: Quod homines, tot conclusions concerning the forms in gene- sententiae: as many minds as men - show ral. ten geologists a problem and at least ten possible explanations will be suggested. And this is admirable, for the greater the CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 113 choice of possible explanation, the greater his model has found wide acceptance (e.g. the chance of the truth eventually emer- OLLIER & TUDDENHAM, 1962; ging; if indeed it can be recognised! But SELBY, 1977), though it leaves much human characteristics and failings have field evidence unexplained and it is also introduced problems. incompatible with some evidence and argument (e.g. TWIDALE, 1982). The value of hindsight HOLMES (1918, p. 93) also referred to scarps which had been worn back by The first stage in the evaluation of a intense localised attack at their base, thus concept or idea is for it to be recognised presaging the basal sapping of cliffs des- for what it purports to be. Some have been cribed by PEEL, (1941, p. 16-18), and introduced as incidental or casual asides which in turn bears on the origin of the which in retrospect can be seen to be mea- piedmont angle (TWIDALE, 1967), ningful and which were grasped and deve- admittedly with an emphasis on surficial loped by later workers. Thus the potential rather than subsurface weathering, but import of KNOPF's (1924, p. 637) com- nevertheless germane to the problem. [It ment that some high level remnants in the should be added that Peel who reviewed northern Appalachians are 'out of reach of that paper was too modest to mention the erosion' has been alluded to in an earlier matter in his report to the journal editor!] section of this essay. Its possible signifi- Of course the authors mentioned may cance was not appreciated for many years, not themselves have appreciated the signi- until Crickmay, who was for a year at Yale ficance of their incidental observations at the same time as Knopf, developed and and comments, but that is unlikely; they used the idea as a the basis for his concept simply did not emphasise or highlight of Unequal Activity (CRICKMAY, 1932, what were, in the contexts in which they 1974,1976). were working at the time, incidental, Parallel scarp retreat has long been almost extrinsic, observations and inferen- appreciated (e.g. FISHER, 1866) but its ces. early application as an explanation of inselbergs is due to HOLMES (1918, p. Out of sight, out of mind 93) who devoted a single sentence to the possibility in a paper on the geology of Conversely, some concepts have been Mozambique which occupied sixty-six recycled and rediscovered many times closely printed pages. Scarp recession was over. Take for instance the two-stage deve- later invoked as an explanation for lands- lopment of granitic boulders. That they cape evolution in King's model of retreat originate by fracture-controlled weathe- and pedimentation (KING, 1942, 1953). ring in the shallow subsurface was appre- He also applied the mechanism to born- ciated at least as early as 1791 (HASSEN- hardt-inselbergs which he interpreted as FRATZ, 1791), and this was noted by the last remnants remaining after long HUTTON (1795, p. 174) in his widely distance scarp retreat (KING, 1949) and read treatise; but the idea was evidently 114 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001) lost and rediscovered many times during science to advance it is sometimes neces- the next 150 years (TWIDALE, 1978). sary to entertain the absurd, for as Thomas Moreover, and arising in part from an Huxley remarked, the 'silly' question is ambiguity which developed concerning frequently the first intimation of a new the meaning of the term 'tor' - some took development. Outrageous hypotheses it to mean a small steep sided tower-like (DAVIS, 1926) have been instrumental in form, 'about the size of a house' (JONES, initiating radical reinterpretations: what 1859; LINTON, 1952), while others, par- is now taken as proved (pro tempore) was ticularly those working in the southern once only imagined. Many of the absurdi- continents, took it to mean a boulder (e.g. ties will prove to be just that, but occasio- WILLIAMS, 1936, HILLS, 1940 b, p. 26- nally one incredible idea will lead to a 28; COTTON, 1948, p. 30; MABBUTT, total revision of understanding. Only by 1952; THOMAS, 1965), while others generating such seemingly ridiculous used it in both senses (LINTON, 1952, explanations, and accepting the obloquy 1955). Indeed, the two-stage concept was that unfortunately so often accompanies extended to larger residuals, namely what them, will science in general, and geo- are now referred to as bornhardts and cas- morphology in particular, advance. tle koppies (FALCONER, 1911, p. 145- In some instances, even at the time 247) and later to tors (LINTON, e.g. problems were defined and resolved, con- 1952, 1955), without reference to the key trary evidence and viable alternative earlier publications. explanations were available. For example, it was known from quarrying experience DISCUSSION in the middle of the last century and ear- lier that rocks expanded on being uncon- The examples discussed raise questions fined, and rock bursts were a recognised as to why some explanations of landscape hazard, yet they were inconsistent with have found ready and enduring acceptance the tensional environment implied by ero- while others have received stubborn rejec- sional offloading. The concept of insola- tion. Are we too much influenced by what tion-induced weathering is revived from we believe, and not willing enough to time to time and persists in texts despite consider the unlikely or even the impossi- Barton’s observations and various experi- ble, even in the face of what we like to call mental work which cast doubt on it. common sense? Are we Anselm, and belie- Bornhardt-inselbergs were long regarded ve in order to understand, or Abelard and as desert and savanna forms yet some of understand in order to believe? It is easy the earliest accounts of the forms derived to be adversely critical in retrospect and it from the humid tropics (e.g. DARWIN, is necessary to bear in mind first that 1846). Why are contrary evidence and events now past were once in the distant argument neglected, and other, demons- future, and second that the interpretations trably dubious, explanations preferred? now in vogue are all subject to modifica- Why, a century or so ago, was the complex tion or rejection in due course. But for overthrust and nappe structure of the CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 115

European Alps (see e.g. COLLET, 1927) suggestion of dudes or fashions, namely accepted, despite the lack of an energy that a lack of constraints may partly source, whereas inability to identify a via- account for the many new ideas generated ble means of moving sialic (continental) by those working in geographically and masses was held against Wegener's theory academically remote regions of the world. of continental drift (WEGENER, 1924; In addition to being stimulated by stran- also TARLING & TARLING, 1971)? ge landscapes and scientifically virg i n Is there, despite its basic innovative lands, the great German explorers of purpose, an innate conservatism in scien- Africa and the brilliant geologists who ce? Or is it, as SHERMAN (1996) has investigated the American West, workers articulated, that there are leaders - or like Jutson and Hills in Australia, King 'dudes' in the modern jargon - whose posi- and du Toit in South Africa, and Logan tion, intellect or personality has led to and Scrivenor in Malaya, may have benefi- their ideas being slavishly followed. From ted from being outside the scientific time to time overarching concepts justi- mainstream, beyond the influence of aca- fiably gain wide consideration, leading to demic hierarchies and systems, and thus them and their implications being applied being less shackled, more daring, in their because they are fashionable, and not thinking. because they are apposite in terms of the The difficulties inherent in recogni- evidence and argument. The peneplain sing the truth carry interesting implica- concept provides a clear example of both tions for our systems of appointment, pro- of these last two factors, with Davis' disci- motion and awards, for natural selection ples uncritically applying the great man's implies that the merits of a particular con- interpretation. Personal factors can also cept will not become clear for some time. lead to dispensations being allowed some An idea may justifiably be hailed as clever but not others. or elegant but intellectual sophistication Such matters, involving what might is not necessarily coincident with truth. mildly be termed academic misjudge- Eventually the problem will resolve itself ments or even discourtesies, surely ought with the effluxion of time, as personal fac- to be discussed. Editorial attitudes are cri- tors go to the grave with their initiators, tical in such situations, for surely objecti- as data becomes more accurate and com- ve, sober, professional comments and res- plete, and by a process of natural selection. ponses ought not only to be allowed but to Eventually someone will investigate the be welcomed? Scientific advance involves history of an idea, or review the work of amiacable disputation. Yet it is not always some worker long since dead, unravel the so, for some editors are unwilling to allow sequence of events and feel sufficiently legitimate disputes involving dubious or wedded to the perceived truth to publish, inconsistent practices to be aired: the liti- and, with the benefit of hindsight, be gious society in which we live has much to right. In varying degrees this has happe- answer for. ned already with Hassenfratz and Holmes, There is an obverse side to Sherman's 116 TWIDALE, C. R. CAD. LAB. XEOL. LAXE 26 (2001)

Crickmay, Peel and Bretz. Truth is the and variously politically incorrect. The daughter of time. Spain of his day was not a democracy in which it was safe to espouse unpopular CONCLUSION causes. But he eventually not only overca- me adversity but in some ways benefited The distinguished British historian from it. He was living proof of Balzac's A.J.P. Taylor has pointed out that all assertion that there is no such thing as a advance comes from nonconformity. But great talent without great will power. He society does not like mavericks, renegades maintained his sense of integrity, and thus and heretics - indeed anyone who asks his ability to be comfortable with himself uncomfortable questions, or challenges when, in an immediate sense at any rate, it the conventional wisdom, and tenacity would have been advantageous, and cer- and a thick skin are as useful in science as tainly easier, to run with the crowd. He in life. Parga Pondal was a rebel in his did not, and we admire, respect and thank time. In modern parlance, he was seriously him for it. CAD. LAB. XEOL. LAXE 26 (2001) Reflections on the fate 117

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