The Cart Ruts of Malta

Home , Geology of Malta

https:/www.cambridge.org/core/terms Downloaded from ∗ eevd eebr20;Acpe:2 ac 08 eie:1 a 2008 May 19 Revised: 2008; March 20 Accepted: 2007; December 4 Received: omto,adealsadsiciecnrbto otesuyo hs intriguing these of patterns study spatial their the their of scales, to various problem at contribution the landforms approach distinctive with to deals a Geomorphology which enables landforms. from perspective and geomorphology hence appropriate erosion, formation, is especially geomorphology of an science the is of focus been major only A previously outcrops. has be this necessity, but of alone, must, geomorphology (1996). ruts Drew their by cart of attempted as basis such the details rendering forms on morphological and Erosional interpreted features Their difﬁcult. original more surface. obscuring Earth’s still time, interpretation the through degraded at become exposed necessarily thus directly when rainfall under an producing without in although 1955), ruts, (BBC conclusion. cart the accepted 1955 along commonly in run and BBC were unequivocal the vehicle by of out types pioneering various carried and which was notable archaeology A experimental 1984). Rubinstein in & venture (Parker Mediterranean the in elsewhere ( and periods Punic Arabic the the BC), is and (1500 Neolithic age Age Their Bronze review later illustrations. comprehensive ( the good occupation included and further variously meticulous provides have 2000) attributions a uncertain: (1993; in Trump culminating Rubinstein (1999). & Hughes 1994), uplands Parker by Tanti 1954; the authors Gracie & numerous on 1934; Ventura Evans by island, provided 1928; 1984; the (Zammit been Gian period since by of considerable was have them part a descriptions to over and west reference 1647, earliest the The in 2). on Abela and Francesco mainly 1 (Figures found limestone coralline are by formed ruts cart Maltese The Introduction them. of plenty are there of so clearance – ground Keywords: route their another reach In try and loads. to limestone moderate carriers the carrying the into 1.40m causing cut of 0.675m, gradually gauge would a carts with that the carts ﬁnd weather two-wheeled They wet by geomorphologists. caused by be examined could here are ruts Malta the of ruts cart rock-cut mysterious The Schaefer Martin & Pearson Alastair Mottershead, Derek applied approach an geomorphology Malta: of ruts cart The ANTIQUITY h usaeesnilysalsaeeoinllnfrsicsdit ufc bedrock surface into incised landforms erosional small-scale essentially are ruts The solution to subject is rock, soluble a as that, limestone soft in created were ruts The K(mi:[email protected]) (Email: UK eateto egah,Uiest fPrsot,Bciga ulig inTrae otmuhP13HE, PO1 Portsmouth Terrace, Lion Building, Buckingham Portsmouth, of University Geography, of Department https:/www.cambridge.org/core 2(08:1065–1079 (2008): 82 at,ucranae atrt,tasot hee vehicles wheeled transport, ruts, cart age, uncertain Malta, c 0 C n h oa eid(ot28B) n agda ieya the as widely as ranged and BC), 218 (post period Roman the and BC) 600 . . https://doi.org/10.1017/S0003598X00097787 . Open University Library c 7) rcso hs etrsaeas rsn nGozo in present also are features these of Traces 870). . , on 1065 30 Jan2017 at02:03:54 , subjectto theCambridgeCore termsofuse,available at ∗

Method The cart ruts of Malta

Figure 1. Location of Malta in the Mediterranean.

and distributions, material properties, surface processes and relationships between processes and forms. Many previous authors have described aspects of the form and distribution of the ruts, whereas material properties and erosion processes have been hitherto little considered. Here we present observations of properties and process, with a focus on the applied forces required to cause the erosion of the ruts. Combining published descriptions with the authors’ own field observations, the defining characteristics of the ruts can be identified as follows:

• They occur as paired parallel grooves incised into bedrock, and extending 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 variable up to a maximum of 0.675m (Gracie 1954). • In cross-section they are commonly v-shaped channels with a rounded ﬂoor; the largest ruts tend to have a rectangular box cross-section. • Some rut cross sections show multiple grooves, with two or three channel 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 major landscape features, such as cols or scarp slopes. • Concentrations may occur at regional route nodes, especially crossing points of high ground.

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Method The cart ruts of Malta

Figure 3. Rut patterns, Misrah Ghar il’Kbir (Clapham Junction), including convergent, anastomosing and quasi parallel forms. The parallel paired nature of the ruts is highlighted in this detailed original survey.

• They may be intermittent in plan, often oblique to contours, and exhibit convergent or crossing patterns (anastomosis), or in the case of ancient quarry sites, parallel patterns (Figure 3).

Whilst there is widespread agreement that the paired ruts are intimately related to the passage of vehicles, there are many unresolved questions concerning their origins. The principal questions are whether they were cut by manual labour to facilitate the passage of vehicles, or eroded by the passage of the vehicles themselves. If the latter, then the question arises as to whether the vehicles were wheeled or travelled on runners, or took the form of inclined shafts strapped to a draught animal (a travois).

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Downloaded from https:/www.cambridge.org/core. Open University Library, on 30 Jan 2017 at 02:03:54, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0003598X00097787 https:/www.cambridge.org/core/terms Downloaded from ucin,i eaint h etcnclpoete ftelclsraerocks. surface local the of properties geotechnical the to relation in Junction), Bin Naxxar), novdi u formation. 1976). rut Farmer in & involved tests Attewell and these 1988 of Gerrard information 1975, number Winkler detailed hardness in (more a found yields strength be and compressive can load, uniaxial controlled a to resistance under measures related point which directly metal scleroscope, hard Shore a the by was penetration test to this in employed instrument The oain.Atog eaieysaldtst ti utbyidctv fterc materials rock the of of that indicative is resistance suitably rock under is of three indicator obtained it from further were dataset, investigated A Data represented. small were strength. relatively samples compressive a replicate the Although Three as locations. conditions. defined standard) is is fail (as required to saturated stress rock observed The the apparatus. cause compression uniaxial to a in directly determined was It n eylwdniisb hs rmCahm ic hs ok r opsdalmost composed cm gm are 2.71 rocks of these density Since a with Clapham. calcite, from mineral Bin those the the by by of shown exclusively densities values low low with variable, very is and density The 3. Table in 2. Table given in details sites petrographic study their three and the 1, at Table outcropping in rocks summarised understanding The to are formation. crucial their are formed for are responsible ruts processes the which the in materials rock ruts the of cart properties The bearing rocks the of properties Material displaces. it that water) weighing (normally dry fluid geotechnical strength by of compressive standard volume samples the hand-sized rocks, determining from local and determined sample the was the of density Rock characteristics applied. resistance were the tests identify to order In Methods to: are paper present the of objectives The objectives Research nvra cl Atwl amr17)terc tegho h ape sn higher no is samples the of On represented. strength sites rock the the between 1976) and Farmer within & both (Attewell that variable scale show very universal values and (UCS) a low strength and a is compressive rock, indicates strength uniaxial the This within rock The components voids. strength. mineral by rock the occupied low between samples bonding consequent and these contact of of proportion lack high relative the of indicative are • • • hssuyi ae nfil bevtoso usa he ie,SnPw a-ag (near tat-Targa Pawl San sites, three at ruts of observations field on based is study This ees niern a hnudrae nodrt oe h ieyntr fvehicles of nature likely the model to order in undertaken then was engineering Reverse h est n opesv tegha esrdfo ape ae tteestsare sites these at taken samples from measured as strength compressive and density The ees nieravhcet ttert n,wt t od eeaesfcetsrs to stress sufficient generate load, its with and, ruts the failure. fit rock to cause vehicle a engineer reverse eurdt vroeterssac fterc aeil;and materials; rock forces, the erosive of the resistance of formed; measure the are a overcome ruts as to stresses, the required applied which of in magnitude and materials nature terrain the the determine of properties material the investigate https:/www.cambridge.org/core em n irhGa-lKi pplryadlclykona Clapham as known locally and (popularly Kbir Ghar-il Misrah and gemma ˙ . https://doi.org/10.1017/S0003598X00097787 US esrsterssac frc oipsdcmrsiestresses. compressive imposed to rock of resistance the measures (UCS) ee otrha,Aati ero atnSchaefer Martin & Pearson Alastair Mottershead, Derek . Open University Library , on 1069 30 Jan2017 at02:03:54 hardness, , subjectto theCambridgeCore termsofuse,available at − 2 h ausi h table the in values the , arocksurfaceproperty. em samples, gemma ˙ Uniaxial

Method The cart ruts of Malta

Table 1. Geological units at the study sites, summarised from Pedley et al. (1976; 2002) and Oil Exploration Directorate (1993). A stack of sedimentary rocks is composed of individual beds which are classiﬁed hierarchically into members embracing related beds; related members are then grouped into formations, as shown in this table. It is the characteristics of the rock at the bed or member level which determine the local response to erosional events. Age Formation Site Member

Miocene Upper Coralline Limestone Misrah Ghar il-Kbir Tal-Pitkal Bingemma˙ Mtarfa Oligocene Lower Coralline Limestone San Pawl tat-Targa, Naxxar Xlendi

Table 2. Petrography of the rocks at the study sites, from microscope observations by Anthony Butcher, and descriptions in Pedley et al. (1976; 2002) and Oil Exploration Directorate (1993). Member Petrography

Tal-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 classiﬁcation after Attewell & Farmer (1976). Density Uniaxial compressive Strength Sample Member (g cm−3)strength(MPa) n Classiﬁcation

Naxx 1 Xlendi 2.60 65.7 3 Medium Bin Mtarfa 2.40 12.3 3 Very weak Clap 1 Tal-Pitkal 2.06 2.7 3 Extremely weak

than medium and as low as extremely weak, confirming the qualitative field observations of Parker and Rubinstein (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 this study are listed in Table 4, in a test to investigate the extent to which rock strength of the rock mass varies between dry and saturated conditions. In all cases the rock is less resistant in the saturated condition, in 2 of 3 cases showing a strength reduction of at least 80 per cent. The implication of this finding is highly significant, for it shows the extent to which the rocks at the cart rut sites are weakened when saturated. Under field conditions, then, when surface rocks are wetted by rain, they become so reduced in strength that they are very susceptible to erosion by applied forces. Table 5 compares Shore hardness values between the exposed field surface and the interior mass. The exposed surface may be affected by surface weathering, and generally carries a cover of lichens. These results show that the more resistant Naxxar rock has surface hardness reduced by lichen cover, whereas the extremely weak Clapham material is strengthened by

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Method The cart ruts of Malta

The cross section form of the ruts is the footprint of the vehicle, and provides significant clues regarding the morphology of the vehicular component which carved them. Cross section form throughout the rut sites varies substantially, especially in respect of width. This should not be surprising, since lateral movement of loose wheels or lateral abrasion by linear runners rounding a curve would cause lateral enlargement of the ruts. The most precise evidence of wheel or runner form is provided by the most restricted cross sections, which most closely represent the form of the vehicular component which formed them. By their very nature, deep and tight ruts are difficult to measure accurately in cross section. At Naxxar, however, a rock-cut trench immediately east of an anti-aircraft post displays cart ruts in section (Figure 4). Because these ruts run laterally across a slope of approximately 5˚, the true base of the erosional rut form is offset slightly in the upslope direction. The cross section form of the eroded rut is that of a Figure 4. Rut cross section, San Pawl tat-Targa Naxxar, canyon narrowing downwards with linear facing west. Note that the rut is tilted to the right, on account sides which grade sharply into a slightly of the sloping ground surface above, and that the floor has a rounded floor, approximately 40mm in subsequent infill of tufa (crystalline calcite) which masks the original centre line of the floor. width. Evidence from several locations at Naxxar corroborates this value as a minimum rut basal width. The strength of the surface materials governs their resistance to stresses and indicates the magnitude of the applied stresses required to cause them to fail. Consideration of material strength therefore permits calculations to be made regarding the mass of the vehicle and the form of traction (see Technical Appendix).

Reverse engineering of the rut-forming vehicles It is now pertinent to consider the nature of the vehicular component which could have formed this cross section. Starting with the hypothesis of a travois, it seems inherently unlikely that a travois with bearers composed of timber alone would be sufﬁciently durable to withstand the abrasive forces caused by travel across the surface of the ground, including rock. An alternative suggestion is that the timber bearers could have been reinforced by having stones lashed to their bearing points. If this were the case, and the nature of the

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Downloaded from https:/www.cambridge.org/core. Open University Library, on 30 Jan 2017 at 02:03:54, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0003598X00097787 https:/www.cambridge.org/core/terms Downloaded from otc ewe odadrc tteests ti h okwihwudpeeetal fail. preferentially would which rock the is it sites, these at rock and wood between contact Bin and listed Clapham is the species of strength hardwood compressive of range The a materials. of Green two timber by the can seasoned of compression of strengths repeated strength compressive by compressive wooden respective rock maximum were the limestone they considering erode by that can that addressed assumption wood likely be simplifying whether most latter of the is issue this with it The erosion, of that wheels. of support imply agent to in the 1984), appear were found Rubinstein observations wheels been & These Parker has 1999). 1918; (Hughes evidence (Fenton contention archaeological hoop effectively iron conclusive more or, an no timber with of although shod formed be agent, been would have erosional as may an such component as force a concentrated Such narrowly wheel. a a by implies applied which section, lateral restricted a and in place, develop. take would would sections and abrasion cross stones mutual basal bearer rut that the rounded likely of more more in hardness that inherently uniformity relative the it for the that make Furthermore, incentive width would stones. no of bedrock bearing be uniformity such would the of There expect size exhibit. not the apparently would sections one rut then minimum stone, on stone were contact h eaietgteso h u rs eto orsget hteoinwsconcentrated was erosion that suggests floor section cross rut the of tightness relative The https:/www.cambridge.org/core i tra01 eil alone Vehicle alone Vehicle Vehicle alone Vehicle 0.17 0.04 0.91 0.25 Tal-Pitkal Mtarfa Xlendi 1 Clap Tal-Pitkal Bin 2 Naxx CONDITIONS SATURATED 1 Clap apeMme vhcetne)atie by attained tonnes) (vehicle Member Sample i tra08 Vehicle Vehicle 0.89 1.21 Mtarfa Xlendi Bin 2 Naxx CONDITIONS DRY stress the the of exceed effects to the conditions including dry failure, factor. and rock concentration saturated surface under confined required for vehicle value loaded critical of Mass 7. Table hfs(0.08 Shafts ek1 Volume (m) Dimensions Deck dimensions Component appropriate of vehicle ruts. a cart construct the to fit requirements to material Timber 6. Table xe1.40 Axle oa .0 254.5 0.509 (8 Total Stays ie ttl 6 (2 (solid) Wheels (total) Sides tal et 19)a agn ewe 0ad6 P.Ti osdrbyecesthe exceeds considerably This MPa. 60 and 40 between ranging as (1999) . . https://doi.org/10.1017/S0003598X00097787 ee otrha,Aati ero atnSchaefer Martin & Pearson Alastair Mottershead, Derek . Open University Library + π × 2.4) × × 0.6 × × 0.6 rtclms flae rtclstress Critical loaded of mass Critical × 2 0.1 × 0.08) × 0.06 × 0.04) .300030.0 0.060 0.03 , on × .200236.0 0.072 0.02 1073 × × . .1 7.0 0.014 0.1 30 Jan2017 at02:03:54 em ok Tbe4 n,gvncompressive given and, 4) (Table rocks gemma ˙ × .2 6.0 0.026 2 .600718.5 0.037 0.06 .0 150.0 0.300 2 , subjectto theCambridgeCore termsofuse,available at ( m 3 ) + + + .6 tonnes 0.665 tonnes 0.636 .5 tonnes 0.956 Mass ( kg )

Method The cart ruts of Malta

At Naxxar the respective compressive strengths of wood and rock are more equally matched, and it is more likely that mutual erosion would take place, with wear of both rock and wheel. Wheels, of course, can be replaced when worn whereas the rutted rock surface remains exposed to continuing erosion. The simplest form of wheeled vehicle is the two-wheeled cart, which was traditional in Malta in historic times and may have dated from much earlier times. The materials required to construct a vehicle with a gauge of 1.4m and an axle clearance (wheel radius) of 0.6m, in the simplest form of a two-wheeled cart can readily be estimated and quantified. It is assumed that such a vehicle would be constructed with timber, a substance with a density of approximately 500 kg m−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 of a tonne. It now becomes possible to include both the estimated mass of the vehicle and the stress concentration factor (see Technical Appendix) in considerations of the vehicular erosion process. The stress concentration factor reduces the critical mass required to cause rock failure by a factor of 10. Part of this critical mass is now accounted for by the mass of the vehicle itself, and part by any load it is carrying. The values produced by these considerations are shown in Table 7. Even under dry conditions, the mass of the unladen vehicle alone is sufficient to cause erosion of the Clapham rock surface. Failure of the rocks at Bingemma˙ and Naxxar requires the vehicle to be loaded with 0.636 and 0.956 tonnes respectively. Under saturated conditions, the vehicle alone is sufficient to cause failure of both the Clapham and Bingemma˙ rocks, whilst in the case of the more resistant Naxxar rock, a relatively modest load of 0.665 tonnes will cause rock failure. These calculations therefore demonstrate that these relatively weak rocks are readily eroded under vehicles of quite modest dimensions and loads.

Discussion The calculations above strongly suggest that a two-wheeled cart is well capable of generating sufficient forces to damage the rock surfaces and, through repeated passages over time, causing the erosion of ruts of depths up to >0.5m. Furthermore, the passage of wheels would appear to account satisfactorily for all the morphological features of the ruts. The sliding movement of a travois creates a shearing force on the ground surface, and a robust vehicle when loaded would be theoretically capable of generating sufficient shear stress to abrade the surface of the rocks considered here, especially if the bearing point of the wooden shaft were tipped with stone. Perhaps the strongest argument against this type of vehicle is presented by Pike (1967), in an extensive review, who found no evidence of transportation by travois anywhere in the Mediterranean region. It is also telling that no convincing evidence of stone reinforcement has been found in Malta (Hughes 1999). In the case of a sled the critical load is applied through runners which, by virtue of their length (say, a metre or more), is applied across a much larger surface area than through the wheel. As a result of this large contact area, under any significant load a substantial frictional

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Method The cart ruts of Malta

delivering a substantial rainfall would be sufficient to saturate and weaken surface rocks such that, given a vehicle mass of up to 0.25 tonnes, the rock surfaces other than Naxxar fail under the passage of the cart alone. Under dry conditions the rocks are somewhat more resistant but even the weakest one at Clapham would appear to be erodible by a single passage of an unloaded cart. With the data obtained in this study, and under the assumptions adopted, these rocks would erode under contemporary climatic conditions by the passage of moderately loaded carts and, in some cases, even unloaded carts. Two lines of evidence, however, suggest that the current rock surface lay under a soil cover prior to the formation of the ruts. First, there are substantial discordances between the rutted routeways and the current bedrock topography. For example, rut tracks may climb through an abrupt 0.5m bedrock step, when an easy slope is readily available close by. Ruts tracks may also head directly toward a deep solution shaft exposed on the rock surface, and then develop a duplicate route which serves as a bypass to this obstacle. If the current bedrock topography were visible at the surface at the time, then surely more sensible and less energy consuming routes would initially have been chosen. Close by and visible from the area of cart ruts at the San Pawl tat-Targa site, Naxxar, quarrying has exposed a section in which a soil cover buries the bedrock topography (rockhead relief) and infills the solution pockets and shafts which form major irregularities in the general plane of the bedrock surface. This section is interpreted as an analogue of the former landscape of the rutted bedrock plain now exposed. Thus initial routes would have been selected at the soil surface, in ignorance of the irregularities in the buried rockhead relief. They would be determined by minor topographic variations in the land surface and, particularly perhaps, by stands of vegetation. Soil erosion by passing feet and wheels, particularly in wet conditions, would cause thinning of the soil cover, gradually exposing the bedrock surface beneath. Initially only the bedrock high points would be exposed, but increasingly the lows also, including the shafts which would eventually be revealed as impassable. Thus bypass routes would be developed. This combined evidence, then, strongly suggests the initial presence of a soil cover obscuring the true nature of the rockhead topography and its associated hazards, which only became visible as erosion by human and vehicular traffic eroded the soil, thereby superimposing existing vehicular trackways on to a gradually emergent rough and rocky surface.

Conclusion The problem of the origin of the Maltese cart ruts is considered on a basis of geotechnical, morphological and archaeological evidence. Rut cross-section forms, as observed in the field, are treated as the locus of forces applied by the passage of vehicles. These forces are estimated in relation to rock strength properties. Under reasonable assumptions, it is demonstrated that the force applied through the contact of a wheel with the rock surface is sufficient to cause the local rocks to fail under quite moderate loads, and under wet conditions, a vehicle alone is sufficient to damage by erosion two of the three rock types tested. Under dry conditions the rocks are more resistant, and only at Clapham does the rock fail under the passage of a cart alone. The considerations set out in this paper show that a wheeled cart,

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Downloaded from https:/www.cambridge.org/core. Open University Library, on 30 Jan 2017 at 02:03:54, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0003598X00097787 https:/www.cambridge.org/core/terms Downloaded from A D mysteries; Maltese two 2: Treasure Buried 1955. BBC. A References Carter Paul discussions. Poulsom and helpful Johnson Andrew for Bill stresses, Grima observations, section Reuben applied thin and of rock cartography, for calculation the Butcher for preparing on Anthony for advice mechanics, Long rock mathematical Dave on tests, for advice geotechnical for Devane the out Mike carrying sections, for thin Butcher Emily rock following: the to due are Thanks Acknowledgements problem. intractable of hitherto materials. capable a are on surface perspective specialisms earth new these involving a evidence, kind providing archaeological this existing of with problem together environmental Considered an solving to make Status. a Heritage than World (2001) merit rather Schneider’s underpins sites factor strongly these environmental most that that an claim uniqueness on this however, founded is, It be one. uniqueness therefore cultural The may concentration. local such of concentration this strength in this in mechanical factor low of contributory occur particularly significant the a they is that rocks be do local may the nowhere It islands. 2001), Maltese the Schneider as abundance 1999; (Hughes region Mediterranean impounded artificially create to scarce it a transporting becomes landscape. by 1928). of soil it (Zammit the conserve that period fields to conditions around a arises environmental need water during such the rock and under formed and resource as precisely were soil is such trackways the It il-Kbir, erosion. the resources is Ghar soil that and likely Misrah suggests More trading, as evidence as erosion. for such Geomorphological such rut produce stones sites for including giant from force of materials, quarried sufficient transportation local create invoke of to to transport need explanation no an is as There megaliths sufficient loads. create the to comprise capacity to the has wheels, two failure. rock with cause one to is force version applied simplest the which of TTEWELL BELA REW hspprdmntae h otiuinta emrhlg n etcnc can geotechnics and geomorphology that contribution the demonstrates paper This the in elsewhere exist trackways rutted similar of occurrences limited Although sufficient been have would goods local that imply above estimated loadings moderate The alra:Uiesttd e Illes Balears. les de Universitat : Mallorca 1995) Soller symposium, 30.5 B nomto rhvs CC 052379. Archives: & Information BBC 13.06.55. geology engineering n ua mat nMla nJJ Forn J.J. in Gin Malta, in impacts human and n14) aet:Mde Books. Midsea Valetta: Bonacota P. 1647). by in Malta in published Club originally Book 1984, Melitensia notitie the altre by ed edition antichita, (facsimile sue le con Siciliano Mare https:/www.cambridge.org/core ..19.Cr usadkre:karstification karren: and ruts Cart 1996. D.P. , ..14.Dladsrtin iMlaIoanel Isola Malta di descrittione Della 1647. G.F. , s(ed.) es ´ ..&IW F I.W. & P.B. , arnlnfrs(International landforms Karren . e ok ase Press. Halsted York: New . https://doi.org/10.1017/S0003598X00097787 ARMER ee otrha,Aati ero atnSchaefer Martin & Pearson Alastair Mottershead, Derek 0–0 am de Palma 403–20. : 1976. . . Open University Library rnilsof Principles s& os ´ A. ` , on 1077 30 Jan2017 at02:03:54 E G F G G H ENTON VANS REEN RACIE ERRARD UGHES Antiquity 339-42. ni Hyman. Unwin 62-78. Islands. the Maltese of tracks ancient the palaeo-landscape: 67-72. T-1) aio W) SDprmn of Agriculture. Department US (WI): Madison GTR-113). material engineering in 4, Chapter 1999. ...13.Mleecart-ruts. Maltese 1934. E.M.P. , .. ..W J.E. D.W., , ..15.Teacetcr-rcso Malta. of cart-tracks ancient The 1954. H.S. , ..11.TeMleecr ruts. cart Maltese The 1918. E.G. , ..19.Pritn etrsfo a from features Persistent 1999. K.J. , ..1988. A.J. , 8 91-8. 28: , subjectto theCambridgeCore termsofuse,available at egahclJournal Geographical ok n landforms. and Rocks INANDY Gn eh et FPL- Rept. Tech. (Gen. odhnbo oda an as Wood – handbook Wood &D.E.K Antiquity RETSCHMANN 165(1): London: Man 18: 8: .

Method The cart ruts of Malta

Oil Exploration Directorate. 1993. Geological map of the SCHNEIDER, G. 2001. Investigating historical trafﬁc Maltese Islands. Valletta: Oil Exploration routes and cart-ruts in Switzerland, Elsass (France) Directorate. and Aosta Valley (Italy). TheOracle(Journalofthe PARKER,R.&M.RUBINSTEIN. 1984. The cart-ruts on Grupp Arkeologiku Malti) 2: 12-22. Malta and Gozo. Malta: Gozo Press. TRUMP, D.H. 1993. Malta: an archaeological guide. PEDLEY, H.M., M.R. HOUSE &B.WAUGH. 1976. The Valletta: Progress Press. geology of Malta and Gozo. Proceedings of the –2000. Malta prehistory and temples. Santa Venera: Geological Association 87(3): 325-41. Midsea Books PEDLEY,M.,M.H.CLARKE &P.GALEA. 2002. Limestone VENTURA,F.&T.TANTI. 1994. The cart tracks at San islands in a crystal sea: the geology of the Maltese Pawl tat-Targa, Naxxar. Melita Historica 11(3): Islands. San Gwann: Publishers Enterprise Group. 219-40. PIKE, G. 1967. Pre-Roman land transport in the WINKLER, E.M. 1975. Stone: properties, durability in western Mediterranean region. Man: New Series man’s environment. Wien: Springer. 2(4): 593-605. ZAMMIT, T. 1928. Prehistoric cart-tracks in Malta. Antiquity 11: 18-125.

Technical Appendix Equation 1 describes the relationship between a vehicle mass (including any load), whether static or moving, and the compressive stress 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 rut basal width), and 0.02m length.

The mass of a vehicle required to cause failure by compression is given by:

4ltσ M = max Equation 1 3

where l, t = length, width of wheel/surface contact M = mass of vehicle σmax = maximum compressive strength of surface material

By setting applied stress equal to rock compressive strength, the vehicle mass required to fail the underlying rock surface can readily be calculated. By setting σmax equal to the compressive strength of the respective rock members, the value of vehicle mass (representing compressive stress) required to cause failure by compression of the rocks can be calculated. The values above rest on the assumption of clean contact between smooth surfaces. In practice, however, this condition is unlikely to be met under field conditions for two reasons. First, the rock surface is rarely perfectly smooth, and is characterised by microvariations in relief and rock composition. These irregularities increase the stress locally on asperities and, on their lateral gradients, translate the compressive stress into a shearing stress. Secondly, the presence of stones and other hard objects at the wheel/rock contact also serves to concentrate stress locally, and also translates into a tensile (splitting) stress tending to prise the rock apart. Since rock materials are substantially less resistant to shear and tensile stresses then compressive ones, these microscale failures will occur at significantly lower levels of applied force than that required to produce failure under simple compression in the ideal case. These microscale processes operating at the wheel/rock contact are the essence of rock breakdown in this case and enable the surface rock to fail at lower levels of applied stress. They are characterised by locally increased levels of applied stress, and the generation of types of stress, shear and tensile stresses, to which materials are substantially less resistant. This combination of higher local stresses and lower resistance means that the values derived from the ideal case have to be revised. They cannot be precisely quantified, since they describe historical situations in which

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Method