Archaeology and soil science: Green Hills, Australia

Robert van de Graaff                                                                                                                     with input from David Rhodes of Heritage Insight 

Over the last two years there have been some interesting applications of soil science and geomorphology to help archaeologists with their search for sites that could contain many Aboriginal artefacts from Pre-Settlement times. The areas eastward from Berwick towards Pakenham are part of a corridor along the Princes Hwy rapidly changing land use making up another “Growth Area” of Greater Melbourne. It is Government policy that these lands be investigated for potential presence of Aboriginal artefacts before wholesale excavation and filling destroy the richest sites. A local company, Heritage Insight Pty Ltd, is a firm that carries out archaeological surveys and excavations, collecting and recording artefacts. Heritage Insight has used old soil maps of the area in the hope of narrowing down the sites where Aboriginal people would have preferred to camp and where they might have left much evidence of their tools and occupation.
Ian Allan of Geocode mapping and Analysis P/L, a geographic information expert, and I pooled our experiences and started to look at the project areas, Green Hills and an area north of Henry Road, Pakenham, in terms of their geomorphology and topography. In this general area, there is much low lying, rather wet country and any uplands would provide permanently dry ground with good views over the surrounds, possibly useful in offering a variety of hunting and gathering environments.

Figure 1 Green Hills is located at the lower occurrence of granite (Dg)

Green Hills was mapped as a granitic outcrop within a broad expanse of Quaternary alluvial silt, clay and sand (Figure 1). On the southern slopes there were a number of well-filled farm dams, notwithstanding years of drought. It was a peculiar feature of these dams that they were at least halfway up the slope and not in a drainage line (Figure 2). One of them had brackish water. It dawned upon us the dams were developed by the farmers where there was a hill side spring that probably runs all year round, surely an attribute of a good camp site. The brackish water may also have been an attraction in terms of its salt content. The hill top had the beginnings of laterite formation and probably was a good highly permeable area for rain infiltration. When we checked the soil there to see from where it came, liberating the sand fraction by washing out all fines under a tap it showed that all quartz and other hard grains were well rounded, and therefore must have been part of an old alluvium that covered the granite. At the base of Green Hills, the sand fraction liberated the same way had all highly angular sharp-edged quartz, derived from the underlying granite.

Figure 2 Hill slope dams (springs) are numbered a, b, c, and d, whereas e and f are dams in drainage lines. Granite-derived angular sand grains are found in dam b. SS stands for “soil scrapes” where trenches were dug to look for artefacts

On the Green Hills property, archaeological excavation carried out by Heritage Insight Pty Ltd found that remains of past Aboriginal campsites occurred predominantly within 200m of the waterholes, but on both the hill and higher elevations of the floodplain. Some of the archaeological sites contained intact elements (deposits of stone artefacts). Analysis of the stratigraphic and spatial distribution of these stone artefacts has provided evidence of some activities that were occurring at Aboriginal campsites in the past. Although the soils appeared to be an older alluvium, radiometric dating of a hearth associated with an archaeological site on the floodplain yielded a recent date of 1390+/- 37 BP (Wk 22626).

Figure 3 The blue line represents the elevated stream channel that follows the spine of the old fan. Springs or soaks emerge to the left. Note also the white line that follows the spine of a secondary fan on the right which may be a cattle track.

At the Henry Road site, we found the best areas for artefacts were on the crest of an old alluvial fan running down towards the south. Walking across the fan I was struck by the very shallow, but continuous grassed “spoon drain” that ran along most of its length. It took a couple of hours of discussion with Ian Allan, who kept prodding me about this “Why would a farmer need a spoon drain along the crest of an elongated sloping land form?”, before I hit upon the idea that this spoon drain was the final vestige of the old stream that built the fan, but had now slipped off it to a deep valley along the west. Checking the aerial photo with contours superimposed (Figure 3) afterwards, the old stream is very clear, as well as a few wet spots that are or were probably useful soaks or springs during Aboriginal occupation. Radiometric dating of one charcoal sample at 600mm yielded a date of 2,255 +/- 41 BP (Wk27299) and a second charcoal sample at 700-800mm was dated to 3,183 +/- 30 BP (Wk27300). Deposits of stone artefacts were found in the alluvial fan from the surface to a depth of 1100mm, in sand overlying a ferruginous clay layer. Investigations are still underway to determine whether the stone artefacts are derived from successive episodes of occupation by Aboriginal people or whether the observed distribution is the product of natural processes, such as bioturbidity. However, the dates obtained from the sand deposits are consistent with the types of stone technology represented in the assemblage at that depth.

This article was first published in Profile, the newsletter of Soil Science Australia, Issue 168, March 2012, and is republished here with the permission of the Author and Soil Science  Australia


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