The cart ruts of Malta: an applied geomorphology approach.

The cart ruts of Malta: an applied geomorphology approach. The mysterious rock-cut cart ruts of Malta are here examined bygeomorphologists. They find that the ruts could be caused by two-wheeledcarts with a gauge of l. 40m carrying moderate loads. In wet weather thecarts would gradually cut into the limestone and reach their groundclearance of 0.675m, causing the carriers to try another route--so thereare plenty of them. Keywords: Malta, uncertain age, cart ruts, transport, wheeledvehicles Introduction The Maltese cart ruts are found mainly on the west part of theisland, on the uplands formed by coralline cor��al��line?adj.1. Of, consisting of, or producing coral.2. Resembling coral, especially in color.n.1. limestone (Figures 1 and 2).The earliest reference to them was by Gian Francesco Abela in 1647, anddescriptions have since been provided by numerous authors over aconsiderable period (Zammit 1928; Evans 1934; Gracie 1954; Parker &Rubinstein 1984; Ventura & Tanti 1994), culminating in a meticulousand comprehensive review by Hughes (1999). Trump (1993; 2000) providesfurther good illustrations. Their age is uncertain: attributions havevariously included the later Bronze Age Bronze Age,period in the development of technology when metals were first used regularly in the manufacture of tools and weapons. Pure copper and bronze, an alloy of copper and tin, were used indiscriminately at first; this early period is sometimes called the (1500 BC), the Punic occupation(c. 600 BC) and the Roman period (post 218 BC), and ranged as widely asthe Neolithic and the Arabic periods (c. 870). Traces of these featuresare also present in Gozo and elsewhere in the Mediterranean (Parker& Rubinstein 1984). A notable and pioneering venture in experimentalarchaeology Experimental archaeology employs a number of different methods, techniques, analyses, and approaches in order to generate and test hypotheses or an interpretation, based upon archaeological source material, like ancient structures or artifacts. was carried out by the BBC BBCin full British Broadcasting Corp.Publicly financed broadcasting system in Britain. A private company at its founding in 1922, it was replaced by a public corporation under royal charter in 1927. in 1955 (BBC 1955), in whichvarious types of vehicle were run along the cart ruts, although withoutproducing an unequivocal and commonly accepted conclusion. The ruts were created in soft limestone that, as a soluble rock, issubject to solution under rainfall when directly exposed at theEarth's surface. Their morphological details thus necessarilybecome degraded through time, obscuring original features and renderinginterpretation still more difficult. Erosional forms such as cart rutsmust, of necessity, be interpreted on the basis of their geomorphology geomorphology,study of the origin and evolution of the earth's landforms, both on the continents and within the ocean basins. It is concerned with the internal geologic processes of the earth's crust, such as tectonic activity and volcanism that constructs new alone, but this has previously only been attempted by Drew (1996). The ruts are essentially small-scale erosional landforms incised incised/in��cised/ (in-sizd��) cut; made by cutting. into surface bedrock outcrops. A major focus of the science ofgeomorphology is erosion, hence geomorphology is an especiallyappropriate perspective from which to approach the problem of theirformation, and enables a distinctive contribution to the study of theseintriguing landforms. Geomorphology deals with landforms at variousscales, their spatial patterns and distributions, material properties,surface processes and relationships between processes and forms. Manyprevious authors have described aspects ofthe form and distributionofthe ruts, whereas material properties and erosion processes have beenhitherto little considered. Here we present observations of propertiesand process, with a focus on the applied forces required to cause theerosion of the ruts. [FIGURE 1 OMITTED] Combining published descriptions with the authors' own fieldobservations, the defining characteristics of the ruts can be identifiedas follows: * They occur as paired parallel grooves incised into bedrock, andextending up to several hundred metres in length. * Each rut pair possesses a constant gauge (distance apart) of c.1.40m, although this may vary slightly between rut pairs. * The width of a rut ranges from 0.04 to 0.10m, with depth variableup to a maximum of 0.675m (Gracie 1954). * In cross-section they are commonly v-shaped channels with arounded floor; the largest ruts tend to have a rectangular boxcross-section. * Some rut cross sections show multiple grooves, with two or threechannel floors, and always replicated in both members of the rut pair. * Locally they may divert in order to avoid obstacles. * In the broader context, ruts are often clearly related to majorlandscape features, such as cols or scarp scarp:see escarpment. slopes. * Concentrations may occur at regional route nodes, especiallycrossing points of high ground. * They may be intermittent in plan, often oblique to contours, andexhibit convergent or crossing patterns (anastomosis anastomosis/anas��to��mo��sis/ (ah-nas?tah-mo��sis) pl. anastomo��ses ? [Gr.]1. communication between vessels by collateral channels.2. ), or in the case ofancient quarry sites, parallel patterns (Figure 3). [FIGURE 2 OMITTED] [FIGURE 3 OMITTED] Whilst there is widespread agreement that the paired ruts areintimately related to the passage of vehicles, there are many unresolvedquestions concerning their origins. The principal questions are whetherthey were cut by manual labour to facilitate the passage of vehicles, oreroded by the passage of the vehicles themselves. If the latter, thenthe question arises as to whether the vehicles were wheeled or travelledon runners, or took the form of inclined shafts strapped to a draughtanimal (a travois travois(trăvoi`), device used by Native North Americans of the Great Plains for transporting their tepees and household goods. It consisted of two poles, lashed one on either side of a dog or, later, a horse, with one end of each pole dragging on ). Research objectives The objectives of the present paper are to: * investigate the material properties of the terrain materials inwhich the ruts are formed; * determine the nature and magnitude of applied stresses, as ameasure of the erosive e��ro��siveadj.Causing erosion. forces, required to overcome the resistance ofthe rock materials; and * reverse engineer a vehicle to fit the ruts and, with its load,generate sufficient stress to cause rock failure. This study is based on field observations of ruts at three sites,San Pawl pawl:see ratchet and pawl. tat-Targa (near Naxxar), Bingemma and Misrah Ghar-il Kbir(popularly and locally known as Clapham Junction), in relation to thegeotechnical properties of the local surface rocks. Methods In order to identify the resistance characteristics of the localrocks, standard geotechnical tests were applied. Rock density wasdetermined from hand-sized samples by dry weighing the sample anddetermining the volume of fluid (normally water) that it displaces.Uniaxial compressive strength Compressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g. (UCS (Universal Character Set) An ISO/IEC format for coding character sets. ISO/IEC 10646 was synchronized with Unicode; however, Unicode adds additional constraints, and compliance with 10646 does not guarantee compatibility with Unicode. See Unicode. ) measures the resistance of rock toimposed compressive com��pres��sive?adj.Serving to or able to compress.com��pressive��ly adv. stresses. It was determined directly in a uniaxialcompression apparatus. The observed stress required to cause the rock tofail is defined as the compressive strength. Data were obtained undersaturated (as is standard) conditions. Three replicate samples wereinvestigated from three locations. Although a relatively small dataset,it is suitably indicative of the rock materials represented. A furtherindicator of rock resistance is that of hardness, a rock surfaceproperty. The instrument employed in this test was the Shorescleroscope, which measures resistance to penetration by a hard metalpoint under a controlled load, and yields a hardness number directlyrelated to uniaxial compressive strength (more detailed information ofthese tests can be found in Winkler Winkler may refer to: Winkler, Manitoba, a Canadian city Winkler (novel), by Giles Coren Winkler (crater), a crater on the Moon Winkler (surname), people with the surname Winkler or Winckler See also 1975, Gerrard 1988 and Attewell& Farmer 1976). Reverse engineering was then undertaken in order to model thelikely nature of vehicles involved in rut formation. Material properties of the rocks bearing cart ruts The properties of the rock materials in which the ruts are formedare crucial to understanding the processes responsible for theirformation. The rocks outcropping at the three study sites are summarisedin Table 1, and their petrographic pe��trog��ra��phy?n.The description and classification of rocks.pe��trogra��pher n. details in Table 2. The density and compressive strength as measured from samples takenat these sites are given in Table 3. The density is variable, with lowvalues shown by the Bingemma samples, and very low densities by thosefrom Clapham. Since these rocks are composed almost exclusively of themineral calcite calcite(kăl`sīt), very widely distributed mineral, commonly white or colorless, but appearing in a great variety of colors owing to impurities. , with a density of 2.71 gm [cm.sup.-2], the values inthe table are indicative of the high proportion of these samplesoccupied by voids. This indicates a relative lack of contact and bondingbetween the mineral components within the rock, and consequent low rockstrength. The uniaxial compressive strength (UCS) values show that rockstrength is low and very variable both within and between the sitesrepresented. On a universal scale (Attewell & Farmer 1976) the rockstrength of the samples is no higher than medium and as low as extremelyweak, confirming the qualitative field observations of Parker andRubinstein (1984). For comparison values for rocks of high strength,such as many granites, often exceed 200 MPa. Shore scleroscope hardness values obtained from the sites in thisstudy are listed in Table 4, in a test to investigate the extent towhich rock strength ofthe rock mass varies between dry and saturatedconditions. In all cases the rock is less resistant in the saturatedcondition, in 2 of 3 cases showing a strength reduction of at least 80per cent. The implication of this finding is highly significant, for itshows the extent to which the rocks at the cart rut sites are weakenedwhen saturated. Under field conditions, then, when surface rocks arewetted by rain, they become so reduced in strength that they are verysusceptible to erosion by applied forces. Table 5 compares Shore hardness values between the exposed fieldsurface and the interior mass. The exposed surface may be affected bysurface weathering, and generally carries a cover of lichens LichensSymbiotic associations of fungi (mycobionts) and photosynthetic partners (photobionts). These associations always result in a distinct morphological body termed a thallus that may adhere tightly to the substrate or be leafy, stalked, or hanging. . Theseresults show that the more resistant Naxxar rock has surface hardnessreduced by lichen lichen(lī`kən), usually slow-growing organism of simple structure, composed of fungi (see Fungi) and photosynthetic green algae or cyanobacteria living together in a symbiotic relationship and resulting in a structure that resembles neither cover, whereas the extremely weak Clapham material isstrengthened by the lichen cover. In the latter case, the lichen coverincreases rock resistance to erosion and thereby acts as a surfaceprotector. Resistance to erosion Two failure modes are possible in eroding a surface by passage oftraffic. The simple direct load of a weight on the surface, as in thecase of a wheel (static or rolling), would create a crushing orcompressive stress Compressive stress is the stress applied to materials resulting in their compaction (decrease of volume). When a material is subjected to compressive stress, then this material is under compression. Usually, compressive stress applied to bars, columns, etc. leads to shortening. . A sliding object, such as a sled or travois, wouldcreate an abrading or shear stress shear stressn.See shear.shear stressA form of stress that subjects an object to which force is applied to skew, tending to cause shear strain. . As a general rule, rocks are aboutsix times more resistant to compression than to shear stresses. The compressive strength values tabulated above were obtained inunconfined conditions. Rock in a confined state, that is, with a topsurface exposed, whilst its body is surrounded by a confining rock massas it would be in field conditions, is approximately 33 per cent moreresistant to compressive stress. Accordingly, we can estimatecompressive and shear strengths for the samples. Since the initialcompressive strength observations were made on saturated samples, theestimates derived from those also represent the saturated condition.Since rock strength is significantly lower under saturated conditions(as demonstrated in Table 4), the values represent wet weather fieldconditions when the rocks are most susceptible to erosion. With known values of resistance, we can DOW estimate the loadingsin relation to both compression and shear stresses that would berequired to cause the rocks to fail, and therefore erode Erode(ĕrōd`), city (1991 urban agglomeration pop. 361,755), Tamil Nadu state, S India, on the Kaveri River. The city is located in a cotton-growing region, and its industries include cotton ginning and the manufacture of transport equipment. , events whichthrough repetition would inevitably lead to the development of theeroded troughs that are the ruts. Force/resistance considerations In creating the ruts, the forces applied to the rock surface wouldhave been a function of the mass (weight) of the loaded vehicles. Inthis way it is possible to determine the forces required to erode therock. By considering the stress requirements and the morphological fieldevidence, it becomes possible to design a vehicle capable of creatingthe ruts; this process is known as reverse engineering. [FIGURE 4 OMITTED] The cross section form of the ruts is the footprint of the vehicle,and provides significant clues regarding the morphology morphologyIn biology, the study of the size, shape, and structure of organisms in relation to some principle or generalization. Whereas anatomy describes the structure of organisms, morphology explains the shapes and arrangement of parts of organisms in terms of such of the vehicularcomponent which carved them. Cross section form throughout the rut sitesvaries substantially, especially in respect of width. This should not besurprising, since lateral movement of loose wheels or lateral abrasion abrasion/abra��sion/ (ah-bra��zhun)1. a rubbing or scraping off through unusual or abnormal action; see also planing.2. a rubbed or scraped area on skin or mucous membrane. by linear runners rounding a curve would cause lateral enlargement ofthe ruts. The most precise evidence of wheel or runner form is providedby the most restricted cross sections, which most closely represent theform ofthe vehicular component which formed them. By their very nature,deep and tight ruts are difficult to measure accurately in crosssection. At Naxxar, however, a rock-cut trench immediately east of ananti-aircraft post displays cart ruts in section (Figure 4). Because these ruts run laterally across a slope of approximately50, the true base of the erosional rut form is offset slightly in theupslope direction. The cross section form of the eroded rut is that of acanyon narrowing downwards with linear sides which grade sharply into aslightly rounded floor, approximately 40mm in width. Evidence fromseveral locations at Naxxar corroborates this value as a minimum rutbasal width. The strength of the surface materials governs their resistance tostresses and indicates the magnitude of the applied stresses required tocause them to fail. Consideration of material strength therefore permitscalculations to be made regarding the mass ofthe vehicle and the form oftraction (see Technical Appendix). Reverse engineering of the rut-forming vehicles It is now pertinent to consider the nature of the vehicularcomponent which could have formed this cross section. Starting with thehypothesis of a travois, it seems inherently unlikely that a travoiswith bearers composed of timber alone would be sufficiently durable towithstand the abrasive forces caused by travel across the surface of theground, including rock. An alternative suggestion is that the timberbearers could have been reinforced by having stones lashed to theirbearing points. If this were the case, and the nature of the contactwere stone on stone, then one would not expect the uniformity of widththat the minimum rut sections apparently exhibit. There would be noincentive for uniformity in the size of such bearing stones.Furthermore, the relative hardness of the bearer stones and bedrockwould make it inherently more likely that mutual abrasion would takeplace, and that more rounded rut basal cross sections would develop. The relative tightness ofthe rut cross section floor suggests thaterosion was concentrated in a restricted lateral section, which impliesa narrowly concentrated force such as would be applied by a wheel. Sucha component may have been formed of timber or, more effectively as anerosional agent, shod shod?v.Past tense and a past participle of shoe.shodVerba past of shoeAdj. 1. with ah iron hoop (Fenton 1918; Parker &Rubinstein 1984), although no conclusive archaeological evidence hasbeen found in support of this latter contention (Hughes 1999). Theseobservations appear to imply that it is most likely that wheels were theagent of erosion, with the simplifying assumption that they were woodenwheels. The issue of whether wood can erode limestone rock by repeatedcompression can be addressed by considering the respective compressivestrengths of the two materials. The maximum compressive strength ofseasoned timber of a range of hardwood species is listed by Green et al.(1999) as ranging between 40 and 60 MPa. This considerably exceeds thecompressive strength of the Clapham and Bingemma rocks (Table 4) and,given compressive contact between wood and rock ar these sites, it isthe rock which would preferentially fail. At Naxxar the respective compressive strengths of wood and rock aremore equally matched, and it is more likely that mutual erosion wouldtake place, with wear of both rock and wheel. Wheels, of course, can bereplaced when worn whereas the rutted rock surface remains exposed tocontinuing erosion. The simplest form of wheeled vehicle Noun 1. wheeled vehicle - a vehicle that moves on wheels and usually has a container for transporting things or people; "the oldest known wheeled vehicles were found in Sumer and Syria and date from around 3500 BC"axle - a shaft on which a wheel rotates is the two-wheeled cart, whichwas traditional in Malta in historic times and may have dated from muchearlier times. The materials required to construct a vehicle with agauge of 1.4m and an axle axlePin or shaft on or with which wheels revolve; with fixed wheels, one of the basic simple machines for amplifying force. Combined with the wheel, in its earliest form it was probably used for raising weights or water buckets from wells. clearance (wheel radius) of 0.6m, in thesimplest form of a two-wheeled cart can readily be estimated andquantified. It is assumed that such a vehicle would be constructed withtimber, a substance with a density of approximately 500 kg [m.sup.-3]. The timber required for such a vehicle is estimated in Table 6.This yields a vehicular mass of 254.5 kg, or approximately a quarter ofa tonne. It now becomes possible to include both the estimated mass of thevehicle and the stress concentration factor (see Technical Appendix) inconsiderations of the vehicular erosion process. The stressconcentration factor reduces the critical mass required to cause rockfailure by a factor of 10. Part of this critical mass is now accountedfor by the mass of the vehicle itself, and part by any load it iscarrying. The values produced by these considerations are shown in Table7. Even under dry conditions, the mass of the unladen unladenadj [weight] → vac��o, sin cargamentounladenadj [ship, weight] → �� videunladenadj [ vehicle alone issufficient to cause erosion of the Clapham rock surface. Failure of therocks at Bingemma and Naxxar requires the vehicle to be loaded with0.636 and 0.956 tonnes respectively. Under saturated conditions, thevehicle alone is sufficient to cause failure of both the Clapham andBingemma rocks, whilst in the case of the more resistant Naxxar rock, arelatively modest load of 0.665 tonnes will cause rock failure. Thesecalculations therefore demonstrate that these relatively weak rocks arereadily eroded under vehicles of quite modest dimensions and loads. Discussion The calculations above strongly suggest that a two-wheeled cart iswell capable of generating sufficient forces to damage the rock surfacesand, through repeated passages over time, causing the erosion of ruts ofdepths up to >0.5m. Furthermore, the passage of wheels would appearto account satisfactorily for all the morphological features of theruts. The sliding movement of a travois creates a shearing force on theground surface, and a robust vehicle when loaded would be theoreticallycapable of generating sufficient shear stress to abrade a��bradev.1. To wear away by mechanical action.2. To scrape away the surface layer from a part.abrade ( the surface ofthe rocks considered here, especially if the bearing point of the woodenshaft were tipped with stone. Perhaps the strongest argument againstthis type of vehicle is presented by Pike (1967), in an extensivereview, who found no evidence of transportation by travois anywhere inthe Mediterranean region. It is also telling that no convincing evidenceof stone reinforcement has been found in Malta (Hughes 1999). In the case of a sled the critical load is applied through runnerswhich, by virtue of their length (say, a metre or more), is appliedacross a much larger surface area than through the wheel. As a result ofthis large contact area, under any significant load a substantialfrictional resistance would exist between runner and rock surface, andthe amount of tractive force required for sliding motion would evidentlybe impracticable. It would also be very difficult to construct aload-bearing timber sledge sledge:see sled. with sufficient reinforcement of the runnersto create a clearance of half a metre or more. A further difficultywould lie in the form of tracks created by sled runners on curves, whichwould necessarily be broader than on straights in order to accommodatethe lateral rotation of the linear runners. Furthermore, tracks made byrigid runners tend to skate across and plane the summits of uneventerrain, thereby missing any hollows (Pike 1967). Neither of thesefeatures of rut morphology has been recognised in Malta. Severalfactors, therefore, appear to militate against mil´i`tate a`gainst´v. t. 1. To argue against; to cast doubt on; - used in reference to facts which tend to disprove a hypothesis; as, the absence of a correlation of budget deficits with inflation militates against any causal relation sled transport in thiscase. Observation by the authors has not produced evidence of any formson the walls of the ruts other than those created by natural weatheringand erosion processes in these locally variable rocks. Observation ofrut walls during this study has produced no evidence, or even hint, ofhuman activity in excavating ruts, such as might be provided by pickmarks. Furthermore, given the geotechnical arguments presented in thispaper, there is no need to invoke human excavation as a formativeprocess. It is concluded, therefore, that the ruts were created simplyby the repeated passage of vehicles, in the form of two-wheeled carts. A feature of these results is the wide variation in threshold loadsfor failure between the different rock types. Whilst the strongest rockis capable of supporting a vehicular mass exceeding one tonne, atClapham the rock would fail under the mass of an unladen vehicle alone.This raises the question of why rut depths do not show a similar rangeof variation between different rock types. Explanation can be sought by considering possible material controlson rut depth. Maximum rut depths, however, are broadly equal on rockswhose material properties vary widely. This can be analysed byconsidering the ratios between maximum and minimum values of ruts depthsand material properties between different rocks. Thus density variesbetween rock types by a factor of 1.73, uniaxial compressive strength by24.3, Shore hardness by 11.62 (wet) and 2.43 (dry). Thus, because of thewide variation in the values of these properties between rock types,none of the properties examined individually acts as a control on rutdepth. It is apparent, therefore, that rut depth is independent of theserock material properties. It is surely not coincidental co��in��ci��den��tal?adj.1. Occurring as or resulting from coincidence.2. Happening or existing at the same time.co��in that maximum rut depths in both thestrongest and the weakest rocks in this study are approximately equal.In the absence of any substantive evidence of differential usage, andany correlation between rut depth and material properties, explanationfor the constancy con��stan��cy?n.1. Steadfastness, as in purpose or affection; faithfulness.2. The condition or quality of being constant; changelessness.Noun 1. of rut depth across different sites and materials mustlie elsewhere. A single common factor may lie in the vehiclesthemselves. It would perhaps be surprising if the remarkable constancyof gauge were not mirrored by other design features, such as wheels.Thus, a ground clearance of 0.675m sufficient to enable passage ofGracie's (1954) deepest rut would, allowing for an axle diameter of0.1m, imply a wheel diameter of 1.45m. In this way, vehicle design wouldimpose a constraint on the development of rut depth on any type ofsubstrate which, when attained, would then become unusable leading toduplication of routes by nearby alternatives. There is no need to invoke climate change, as some authors havedone, in deriving explanations of rut erosion. Geotechnicalconsiderations have shown that a rainy day delivering a substantialrainfall would be sufficient to saturate sat��u��ratev. Abbr. sat.1. To imbue or impregnate thoroughly.2. To soak, fill, or load to capacity.3. To cause a substance to unite with the greatest possible amount of another substance. and weaken surface rocks suchthat, given a vehicle mass of up to 0.25 tonnes, the rock surfaces otherthan Naxxar fail under the passage of the cart alone. Under dryconditions the rocks are somewhat more resistant but even the weakestone at Clapham would appear to be erodible by a single passage of anunloaded cart. With the data obtained in this study, and under theassumptions adopted, these rocks would erode under contemporary climaticconditions by the passage of moderately loaded carts and, in some cases,even unloaded carts. Two lines of evidence, however, suggest that the current rocksurface lay under a soil cover prior to the formation of the ruts.First, there are substantial discordances between the rutted routewaysand the current bedrock topography. For example, rut tracks may climbthrough an abrupt 0.5m bedrock step, when an easy slope is readilyavailable close by. Ruts tracks may also head directly toward a deepsolution shaft exposed on the rock surface, and then develop a duplicateroute which serves as a bypass to this obstacle. If the current bedrocktopography were visible at the surface at the time, then surely moresensible and less energy consuming routes would initially have beenchosen. Close by and visible from the area of cart ruts at the San Pawltat-Targa site, Naxxar, quarrying has exposed a section in which a soilcover buries the bedrock topography (rockhead relief) and infills thesolution pockets and shafts which form major irregularities in thegeneral plane of the bedrock surface. This section is interpreted as ananalogue of the former landscape of the rutted bedrock plain nowexposed. Thus initial routes would have been selected at the soilsurface, in ignorance of the irregularities in the buried rockheadrelief. They would be determined by minor topographic variations in theland surface and, particularly perhaps, by stands of vegetation. Soilerosion by passing feet and wheels, particularly in wet conditions,would cause thinning of the soil cover, gradually exposing the bedrocksurface beneath. Initially only the bedrock high points would beexposed, but increasingly the lows also, including the shafts whichwould eventually be revealed as impassable. Thus bypass routes would bedeveloped. This combined evidence, then, strongly suggests the initialpresence of a soil cover obscuring the true nature of the rockheadtopography and its associated hazards, which only became visible aserosion by human and vehicular traffic eroded the soil, therebysuperimposing existing vehicular trackways on to a gradually emergent emergent/emer��gent/ (e-mer��jent)1. coming out from a cavity or other part.2. pertaining to an emergency.emergent1. coming out from a cavity or other part.2. coming on suddenly. rough and rocky surface. Conclusion The problem of the origin of the Maltese cart ruts is considered ona basis of geotechnical, morphological and archaeological evidence. Rutcross-section forms, as observed in the field, are treated as the locusof forces applied by the passage of vehicles. These forces are estimatedin relation to rock strength properties. Under reasonable assumptions,it is demonstrated that the force applied through the contact of a wheelwith the rock surface is sufficient to cause the local rocks to failunder quite moderate loads, and under wet conditions, a vehicle alone issufficient to damage by erosion two of the three rock types tested.Under dry conditions the rocks are more resistant, and only at Claphamdoes the rock fail under the passage of a cart alone. The considerationsset out in this paper show that a wheeled cart, of which the simplestversion is one with two wheels, has the capacity to create sufficientapplied force to cause rock failure. The moderate loadings estimated above imply that local goods wouldhave been sufficient to comprise the loads. There is no need to invoketransportation of giant stones such as megaliths For the record label, see .A megalith is a large stone which has been used to construct a structure or monument, either alone or together with other stones. Megalithic as an explanation tocreate sufficient force for rut erosion. More likely is the transport oflocal materials, including produce for trading, and resources such asrock quarried from sites such as Misrah Ghar il-Kbir, soil and wateraround the landscape. Geomorphological ge��o��mor��phol��o��gy?n.The study of the evolution and configuration of landforms.geo��mor evidence suggests that thetrackways were formed during a period of soil erosion. It is preciselyunder such environmental conditions that soil becomes a scarce resourceand the need arises to conserve it by transporting it to createartificially impounded fields (Zammit 1928). Although limited occurrences of similar rutted trackways existelsewhere in the Mediterranean region (Hughes 1999; Schneider 2001),nowhere do they occur in such abundance as the Maltese islands Maltese Islands:see Malta. . It maybe that the particularly low mechanical strength of the local rocks is asignificant contributory con��trib��u��to��ry?adj.1. Of, relating to, or involving contribution.2. Helping to bring about a result.3. Subject to an impost or levy.n. pl. factor in this local concentration. Theuniqueness of this concentration may therefore be founded on anenvironmental factor rather than a cultural one. It is, however, thisuniqueness that most strongly underpins Schneider's (2001) claimthat these sites merit World Heritage Status. This paper demonstrates the contribution that geomorphology andgeotechnics Geotechnics (synonymous: Geotechnique) is the application of scientific methods and engineering principles to the acquisition, interpretation, and use of knowledge of materials of the Earth's crust and earth materials for the solution of engineering problems. can make to solving an environmental problem of this kindinvolving earth surface materials. Considered together with existingarchaeological evidence, these specialisms are capable of providing anew perspective on a hitherto intractable problem. Technical Appendix Equation 1 describes the relationship between a vehicle mass(including any load), whether static or moving, and the compressivestress it applies to the surface beneath it. This calculation assumes: * plane surfaces of both wheel and rock; * perfect clean contact; * a two-wheeled vehicle; * a contact area of 0.04m tread width (implied by the minimum rutbasal width), and 0.02m length. The mass of a vehicle required to cause failure by compression isgiven by: M = 4lt[[sigma].sub.max]/3 Equation 1 where l, t = length, width of wheel/surface contact M = mass of vehicle [[sigma].sub.max] = maximum compressive strength of surfacematerial By setting applied stress equal to rock compressive strength, thevehicle mass required to fail the underlying rock surface can readily becalculated. By setting [[sigma].sub.max] equal to the compressivestrength of the respective rock members, the value of vehicle mass(representing compressive stress) required to cause failure bycompression of the rocks can be calculated. The values above rest on the assumption of clean contact betweensmooth surfaces. In practice, however, this condition is unlikely to bemet under field conditions for two reasons. First, the rock surface is rarely perfectly smooth, and ischaracterised by microvariations in relief and rock composition. Theseirregularities increase the stress locally on asperities and, on theirlateral gradients, translate the compressive stress into a shearingstress shearing stressn.See shear. . Secondly, the presence of stones and other hard objects at thewheel/rock contact also serves to concentrate stress locally, and alsotranslates into a tensile tensile,adj having a degree of elasticity; having the ability to be extended or stretched. (splitting) stress tending to prise the rockapart. Since rock materials are substantially less resistant to shearand tensile stresses then compressive ones, these microscale failureswill occur at significantly lower levels of applied force than thatrequired to produce failure under simple compression in the ideal case.These microscale processes operating at the wheel/rock contact are theessence of rock breakdown in this case and enable the surface rock tofail at lower levels of applied stress. They are characterised bylocally increased levels of applied stress, and the generation of typesof stress, shear and tensile stresses, to which materials aresubstantially less resistant. This combination of higher local stresses and lower resistancemeans that the values derived from the ideal case have to be revised.They cannot be precisely quantified, since they describe historicalsituations in which small surface irregularities, and small particles ofunknown magnitude and composition take part, and are variables ofunknown and unknowable un��know��a��ble?adj.Impossible to know, especially being beyond the range of human experience or understanding: the unknowable mysteries of life. magnitude. Nevertheless, in practice such microeffects are commonly accommodated by reducing the applied force requiredto cause failure by a factor of up to 10, termed the stressconcentration factor. Equation 1 can now be modified to incorporate thestress concentration factor, as follows: M = 4lt[[sigma].sub.max]/30 Equation 2 Acknowledgements Thanks are due to the following: Emily Butcher for carrying out thegeotechnical tests, Dave Long David ("Dave") Long (born November 21st, runner]] from Great Britain, who represented the United Kingdom in the men's marathon at the 1988 Summer Olympics in Seoul, South Korea. There he finished in 21st position, clocking 2:16:18. for preparing rock thin sections, MikeDevane for mathematical advice on calculation of applied stresses,Andrew Poulsom for advice on rock mechanics Rock mechanics is the theoretical and applied science of the mechanical behaviour of rock and rock masses; it is that branch of mechanics concerned with the response of rock and rock masses to the force fields of their physical environment. , Anthony Butcher for rockthin section observations, Bill Johnson Bill Johnson may refer to: Bill Johnson (jazz musician) (1874–1972), American jazz musician Bill Johnson (entrepreneur) (1905-1962), First Importer of Triumph Motorcycles 1930's Bill Johnson (skier) (born 1960), American skier and Paul Carter Paul Carter is the name of: Paul Carter (academic) (born 1951), historian, writer, artist and interdisciplinary scholar at the University of Melbourne Paul Carter (politician), councillor on Stockport Metropolitan Borough Council for thecartography cartography:see map. cartographyor mapmakingArt and science of representing a geographic area graphically, usually by means of a map or chart. Political, cultural, or other nongeographic features may be superimposed. , and Reuben Grima for helpful discussions. References ABELA, G.F. 1647. Della descrittione di Malta Isola nel MareSiciliano Si`ci`li`a´non. 1. A Sicilian dance, resembling the pastorale, set to a rather slow and graceful melody in 12-8 or 6-8 measure; also, the music to the dance. con le sue antichita, ed altre notitie (facsimile edition bythe Melitensia Book Club 1984, originally published in Malta by P.Bonacota in 1647). Valetta: Midsea Books. ATTEWELL, P.B. & I.W. FARMER. 1976. Principles of engineeringgeology. New York New York, state, United StatesNew York,Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of : Halsted Press. BBC. 1955. Buried Treasure buried treasure - A surprising piece of code found in some program. While usually not wrong, it tends to vary from crufty to bletcherous, and has lain undiscovered only because it was functionally correct, however horrible it is. 2: two Maltese mysteries; 13.06.55. BBCInformation & Archives: CC 052379. DREW, D.E 1996. Cart ruts and karren The Karren is a mountain in Bregenzerwald, part of the Northern Limestone Alps in Vorarlberg, Austria.Karren is the terms used to describe the micro-solutional feature that form on exposed limestone surfaces. : karstification and humanimpacts in Malta, in J.J. Fornos & A. Gines (ed.) Karren landforms(International symposium, Soller 1995): 403-20. Palma de Mallorca :Universitat de les Illes Balears. EVANS, E.M.P. 1934. Maltese cart-ruts. Antiquity 8: 339-42. FENTON, E.G. 1918. The Maltese cart ruts. Man 18: 67-72. GERRARD, A.J. 1988. Rocks and landforms. London: Unwin Hyman. GRACIE, H.S. 1954. The ancient cart-tracks of Malta. Antiquity 28:91-8. GREEN, D.W., J.E. WINANDY & D.E. KRETSCHMANN. 1999. Chapter 4,in Wood handbook-Wood as an engineering material (Gen. Tech. Rept.FPL-GTR-113). Madison (WI): US Department of Agriculture. HUGHES, K.J. 1999. Persistent features from a palaeo-landscape: theancient tracks of the Maltese Islands. Geographical Journal 165(1):62-78. Oil Exploration Directorate. 1993. Geological map of the MalteseIslands. Valletta: Oil Exploration Directorate. PARKER, R. & M. RUBINSTEIN. 1984. The cart-ruts on Malta andGozo. Malta: Gozo Press. PEDLEY, H.M., M.R. HOUSE & B. WAUGH. 1976. The geology of Maltaand Gozo. Proceedings of the Geological Association 87(3): 325-41. PEDLEY, M., M.H. CLARKE & P. GALEA. 2002. Limestone islands ina crystal sea: the geology of the Maltese Islands. San Gwann: PublishersEnterprise Group. PIKE, G. 1967. Pre-Roman land transport in the westernMediterranean region. Man: New Series 2(4): 593-605. SCHNEIDER, G. 2001. Investigating historical traffic routes andcart-ruts in Switzerland, Elsass (France) and Aosta Valley (Italy). TheOracle (Journal of the Grupp Arkeologiku Malti) 2:12-22. TRUMP, D.H. 1993. Malta: ah archaeological guide. Valletta:Progress Press. --2000. Malta prehistory prehistory,period of human evolution before writing was invented and records kept. The term was coined by Daniel Wilson in 1851. It is followed by protohistory, the period for which we have some records but must still rely largely on archaeological evidence to and temples. Santa Venera: Midsea Books VENTURA, F. & T. TANTI. 1994. The cart tracks ar San Pawltat-Targa, Naxxar. Melita Historica 11 (3): 219-40. WINKLER, E.M. 1975. Stone: properties, durability in man'senvironment. Wien: Springer. ZAMMIT, T. 1928. Prehistoric cart-tracks in Malta. Antiquity 11:18-125. Derek Mottershead, Alastair Pearson Alastair Pearson DSO (1915 - 1995) was a baker and farmer and one of the most highly-regarded soldiers of the British Army who served in World War II. Pearson was born in Glasgow on 1 June 1915. After leaving school, he worked as a baker and enlisted in the Territorial Army. , & Martin Schaefer * * Department of Geography, University of Portsmouth Portsmouth seems better placed than most Post-1992 universities to deal with the surge of applications encouraged by the government's target that 50% of those under-35 should experience Higher Education at some point in their life. , BuckinghamBuilding, Lion Terrace, Portsmouth PO1 3HE, UK (Email: derek,mottershead@port.ac.uk)Table 1. Geological units at the study sites, summarised from Pedley etat (1976; 2002) and Oil Exploration Directorate (1993). A stack ofsedimentary rocks is composed of individual beds which are classifiedhierarchically into members embracing related beds; related members arethen grouped into formations, as shown in this table. It is thecharacteristics of the rock at the bed or member level which determinethe local response to erosional events.Age Formation Site MemberMiocene Upper Coralline Misrah Ghar il-Kbir Tal-Pitkal Limestone Bingemma MtarfaOligocene Lower Coralline San Pawl tat-Targa, Xlendi Limestone NaxcarTable 2. Petrography of the rocks at the study sites, from microscopeobservations by Anthony Butcher, and descriptions in Pedley et al.(1976; 2002) and Oil Exploration Directorate (1993).Member PetrographyTal-Pitkal Coarse grained wackestones/packstones with coralline algae and corals.Mtarfa Thickly bedded carbonate mudstone/wackestone, crystalline with micritic matrix, algal biostrome with foraminifera and shell fragments.Xlendi Coarse grained crystalline limestone with micritic matrix, and abundant coralline fragments and foraminifera.Table 3. Density and UCS for three sites, with strength classificationafter Attewell & Farmer (1976).Sample Member Density Uniaxial (g [cm.sup.-3]) compressive strength (MPa)Naxx 1 Xlendi 2.60 65.7Bin Mtarfa 2.40 12.3Clap 1 Tal-Pitkal 2.06 2.7Sample Member n Strength ClassificationNaxx 1 Xlendi 3 MediumBin Mtarfa 3 Very weakClap 1 Tal-Pitkal 3 Extremely weakTable 4. Rock mass strength in dry and wet conditions, as determined byShore scleroscope.Sample Member UCS (MPa) Dry interiorNaxx 2 Xlendi 63.00 49.92Bin Mtarfa 12.30 36.88Clap 1 Tat-Pitkal 2.70 20.48Sample Member Wet interior Difference (%)Naxx 2 Xlendi 37.64 -24.6Bin Mtarfa 7.36 -80.0Clap 1 Tat-Pitkal 3.24 -84.2Table 5. Comparison of surface and interior scleroscope hardness underdry conditions. Interior ShoreSample Member UCS (MPa) hardness (dry)Naxx 2 Xlendi 63.0 49.92Bin Mtarfa 12.3 36.88Clap 1 Tal-Pitkal 2.7 12.36 Surface ShoreSample Member hardness (dry) Difference (%)Naxx 2 Xlendi 13.40 -73.2Bin Mtarfa 31.32 -15.1Clap 1 Tal-Pitkal 13.88 12.2Table 6. Timber material requirements to construct a vehicle ofappropriate dimensions to fit the cart ruts.Component Dimensions (m) Volume ([m.sup.3])Deck 1 x 2 x 0.03 0.060Sides (total) 6 x 0.6 x 0.02 0.072Wheels (solid) (2 [pi] x 0.6 x 0.04) x 2 0.300Axle 1.40 x 0.1 x 0.1 0.014Shafts (0.08 x 0.08) x 2 0.026Stays (8 + 2.4) x 0.06 x 0.06 0.037Total 0.509Component Dimensions (m) Mass (kg)Deck 1 x 2 x 0.03 30.0Sides (total) 6 x 0.6 x 0.02 36.0Wheels (solid) (2 [pi] x 0.6 x 0.04) x 2 150.0Axle 1.40 x 0.1 x 0.1 7.0Shafts (0.08 x 0.08) x 2 6.0Stays (8 + 2.4) x 0.06 x 0.06 18.5Total 254.5Table 7. Mass of loaded vehicle required under saturated and dryconditions to exceed the critical value for confined surface rockfailure, including the effects of the stress concentration factor.Sample Member Critical mass of loaded Critical stress (vehicle tonnes) attained byDRY CONDITIONSNaxx 2 Xlendi 1.21 Vehicle + 0.956 tonnesBin Mtarfa 0.89 Vehicle + 0.636 tonnesClap 1 Tal-Pitkal 0.25 Vehicle aloneSATURATED CONDITIONSNaxx 2 Mendi 0.91 Vehicle + 0.665 tonnesBin Mtarfa 0.17 Vehicle aloneClap 1 Tal-Pitkal 0.04 Vehicle alone