Late Viking Site ARCHAEOLOGY (Colley 1983, 159)
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23 CHAPTER 3: THE NATURAL HISTORY AND Age site and twenty-three species on a Late Viking site ARCHAEOLOGY (Colley 1983, 159). Crustaceans, especially crabs, seem to have been caught for food from earliest times. 3.1 INTRODUCTION The shoreline of the Western Isles varies greatly ranging from large expanses of sandy beaches to rocky shores and It may seem a little strange to include an account of the is- cliffs and each of these provides habitats ranging from open lands natural history in an archaeological report but just as the water to cliff top and including the upper shore and the physical environment sets limits on the possibilities for settle- intertidal zone. This variety encompasses a wide range of ment through time so also do the natural resources for flesh, vegetational and faunal resources and was of vital importance fish, fowl and vegetation have an economic significance for in early as well as more recent times. early settlers. Between them, the physical background and the At the highest levels of the shore can be found growths of natural resources of an area define an envelope of potential for channel and flat wrack. The bladderless form of wrack is the settlement which expands and contracts with the varying for- main vegetation of the intertidal zone. Also present in certain tunes of time. Social organisation forms part of the definition conditions are Lithothamnion, Alaria esculent (tangleweed) of this envelope and by appropriate strategic adaptation facili- and various algae (Darling & Boyd 1964, 182). The shores of tates or hinders settlement potential also. In this Chapter then the sea lochs are dominated by fucoid weeds including knot- the framework of this envelope is explored. ted and flat wrack. These wracks can be used a fertiliser and as food for sheep and cattle. At low tide carragheen and dulse, both valuable foods for humans, could be gathered. 3.2 NATURAL HISTORY Most importantly, however, the coastal zone contained the richest fauna of any of the islands zones, including mollusca, The Western Isles can be divided into six general ecological mammals, fish and birdlife. zones which also constitute economic resource zones (Figure The marine mammals are, and probably were in prehis- 8). Ranged west to east they form a series of parallel linear tory, a much more important resource than their terrestrial units consisting of open water, shore, machair lands, counterparts. The grey seal population of the Western Isles is backlands, skinned lands and peatlands, before returning to one of the largest in the world and the common seal is also shore and sea on the east side of the island. plentiful in the area. Archaeological data provides ample evi- Two of these zones are artificial, or at least partly so. dence for their early exploitation. Indeed by the Early Chris- Skinned lands consist of former peatlands that have been tian Period, some rookeries were regarded as the private stripped down to a thin layer of peat which, when dug into the property of individual settlements (Anderson & Anderson underlying mineral material, can form a useful agricultural 1961, 2956; McCormick 1981, 317). Cetaceans, either de- soil. The backlands occur where calcareous sands from the liberately hunted or accidentally stranded were an occasional machair combine with peats, a process which can produce the resource available to the inhabitants of the area and their ex- richest agricultural soils of the Western Isles. This can occur ploitation by early man has been demonstrated by excavation naturally when wind-transported machair-sand falls onto the (Clarke 1960, 169). peatlands. They are also artificially created or extended by the The varied coastline of the Isles is rich in mollusca with a deliberate addition of sand, seaweed or other manures and by greater diversity of species in sheltered areas than on the more cultivation, grazing and trampling of livestock, ultimately to exposed and rocky shores (Smith 1979, 179). Excavations sug- produce the rich plaggen soils known as Lewisian Black Earths gest that shellfish were collected at all periods. The mollusca of (Whittow 1977, 2856). The flora and fauna of these six zones rocky shorelines, such as winkle and limpet, were relatively are grouped below, into two ecosystems; the marine ecosys- heavily exploited while the more valuable food species, like tem, consisting of the sea and shore, and the terrestrial ecosys- cockle or oyster, of the sandy shores, although present, are tem, consisting of the other four zones. rare. Shellfish are also used as fish-bait and the apparent pref- erence for less edible species may be explained by their use for fishing rather than their routine inclusion in the human diet. 3.2.1 The marine ecosystem However, their use as famine food, ie as a resource to be ex- ploited in times of food shortage may account for their occa- The marine ecosystem consists, for our purposes, of the sionally abundant presence on the sites considered here. open sea, the inshore waters and sea lochs and the extensive and varied shoreline of the Outer Hebrides. Both open sea and inshore waters are rich in a wide variety of fish. In the 3.2.2 The terrestrial ecosystem (including rivers and inland Mesolithic levels of the Oronsay shell middens, saithe lakes) (coalfish) constitute over 90% of the fish bone material and are in many contexts the only species present (Mellars & Peatland Wilkinson 1980; Mellars 1987). This species is probably the Peat now covers most of the surface of the Western Isles, easiest to catch from the shore. Data from later period sites ranging from the eastern seaboard to the western machair on the Western Isles is scarce but an Iron age midden on lands. The peatlands, especially of the Uists, are interspersed Lewis produced mostly cod as well as ling, pollock and with fresh-water lakes (Plate 10), most of which drain to the saithe (Baden-Powell & Elton 1937, 359). This increase in sea and are colonised by migratory fish. While the fauna of the range of fish caught through time has been more clearly the peatlands extend into the agriculturally rich black-, and demonstrated on the Orkney Islands where ten species were skinned-lands, the flora of these zones is largely artificial and noted on a Neolithic/Bronze Age site, thirteen on an Iron varies with their current agricultural use. 24 Figure 8. Ecological units on the Western Isles. The physical relief of the Outer Hebrides contributes to their zonation in north/south strips. Land under 8 m is concentrated in a strip of machai r plains along the west coast. Small seasonal lochs (not illustrated on this scale) and extensive shallow permanent lakes lie between the machai r and the high ground. The latter is peat covered and stretches north south along the east coast. The west coast descends into the sea in a shallow slope (averaging 1 in 250), while the east coast is steep-to and the sea plunges steeply to depths of 300 m or more. 25 Plate 10. Knock-and-lochan, or hill and loch, in North Uist The peatlands today support a typical heathland vegeta- than historical interest. Blackburn studied samples from tion dominated by Erica tetralix interspersed with mosses Calvay Island and Stoneybridge, South Uist (Blackburn 1946; such as Racomitrium lanuginosum. On better drained slopes Heslop-Harrison & Blackburn 1946), but seems to have as- Calluna dominates the vegetation while deeper peat carries sumed that the sampled peat began to form about 6000 BC, more Molinia, due to the high acidity of the drainage water. an assumption which may have been unwarranted. In general Less acidic peats carry a high proportion of Eriophorum her diagrams indicate that non-arboreal pollen predominated (Darling 1955, 161). In the past, peatlands provided rough throughout prehistory. Analyses of now intertidal peats, un- grazing and peat was used as fuel, animal bedding, roofing dertaken as part of Ritchies geomorphological researches and as a fertiliser for machair soils. Peat is still extensively (1966), are somewhat schematic and the results reflect condi- used as fuel but its other uses, evidenced in these excavations, tions in the immediate environs of the freshwater lakes in have been largely usurped by modern materials. which the peat deposits originally formed. Pollen analysis was undertaken on a sediment sequence Machair from Little Loch Roag, West Lewis, covering the period from The high pH of its calcareous sands is responsible for the 9140 ± 140 uncal BP (Q-1531) to date (Birks & Madsen machairs distinctive grassland vegetation now dominated by 1979, 825). This reaffirms the general lack of woodland devel- Festuca rubra, both on the low machair and the stabilised opment, a factor the authors attribute to exposure. At its most high machair. The agricultural potential and limitations of developed, the vegetation cover seems to have consisted of a machair lands are discussed above (Chapter 1); they provide mosaic of grassland, heath and tall-herb communities with oc- moderate to poor grazing which is susceptible to damage by casional birch and hazel scrub. The earliest evidence for hu- overgrazing. Cultivation can only be sustained when accom- man influence in this deposit was detectable at levels dating to panied by constant manuring and a generous rotation cycle. approximately 19002000 BC (Birks & Birks 1980). Peat deposits from Tob nan Leobag, near Callanish, were The vegetational history of the terrestrial system. investigated by Bohncke (1988), as part of an investigation of Erdtmans pollen analysis (1924, 486 et seq) of material from sub-peat field fences in that area. The sequence runs from some twenty sites in Lewis is the earliest pollen work to have about 6000 BC to date. Bohncke suggests that, until roughly been undertaken in the Isles, although it is now of little more 2000 BC, the landscape supported pockets of birchwood.