Reading between the Giant’s Causeway basalts
One striking feature of the cliffs at Giant’s Causeway, Northern Ireland, is an orange bed that forms a prominent band in the sheer basalt face. This bed creates a natural bench and the cliff path follows it around the bays. It is 10–12 metres (30–40 ft) thick and composed of soft, friable, red and brown material. Technically it’s called the Interbasaltic Bed—i.e. the bed between the basalts.1,2
The standard story is that the Inter-basaltic Bed is a thick soil that formed by weathering over an unimaginably long time. For example, the website of the Giant’s Causeway Visitors’ Centre says of that layer, “During 2 million years of warm, wet climate the lower basalt weathered to form a deep red rock called ‘Laterite’.”3 On the face of it, this seems to be an argument for long ages and to contradict the biblical timescale.
However, such soil is unlike any forming in the United Kingdom today, so geologists propose that in the past the climate was warm and wet like tropical Africa. They say the exposed top of the Lower Basalt weathered into a thick soil that supported lush vegetation for perhaps two million years. Then the next lava flow erupted and covered the landscape.4
However, there are problems with this idea:
- The bed contains no soil horizons (e.g. an organic horizon or a clay horizon).
- Ireland is not at tropical latitudes now, nor when the Causeway formed.
- There is no evidence that roots once grew in the loose material.
- The soft bed contains lignite (brown coal) which washed into place as vegetation.5
- Weathering over millions of years would not produce a soil bed with such an even thickness.
- Where the bed slopes down near Giant‘s Causeway itself, there should be evidence of an ancient watercourse, but there isn’t.
- In two million years, tropical weathering would remove many hundreds of metres of material, yet the Lower Basalts appear hardly touched.
- The boundary between the altered material and the basalt is not very thick, but long-term weathering would penetrate deeply down the joints and into the rock.
- Weathering cuts into a landscape producing valleys and gorges, yet the surface of the Lower Basalts is still relatively smooth.
- There is no baked soil or burnt vegetation. If the Causeway basalt erupted onto an ancient land surface, it would bake the top of the bed underneath.
So although on first glance the bed looks like a soil, on closer examination it is clear that it was not formed by slow-and-gradual weathering over a long period of time. Rather, the thick bed was buried quickly by the later lava flow, and chemically altered by the heat that remained after the lava had been quenched in the retreating floodwaters. Interpreting the Interbasaltic Bed within a biblical Flood framework makes better sense than long-age explanations.
[Update 22 August 2011]. As shown in the diagram above, the basalt flows comprising Giant’ Causeway erupted during the Abative phase (or Sheet-flow phase) of the global Flood, as the floodwaters were receding from the continents. The thick bed of sediment, which also contained vegetation, was rapidly deposited by the receding waters on top of one of the lava flows and covered quickly by the next basaltic flow. Heat and fluids from the basalt combined with the abundant water in the sediment chemically altered the bed and coalified the vegetation within it. The presence of abundant water prevented the sedimentary bed from being baked by the subsequent lava flow.
- Wilson, H.E., Regional Geology of Northern Ireland, Geological Survey of Northern Ireland, Belfast, pp. 63–64, plate 9B, 1986. Return to text.
- Lyle, P., A Geological Excursion Guide to The Causeway Coast, W&G Baird, Antrim, Northern Ireland, pp. 24–25, 1998. Return to text.
- Giant’s Causeway Visitors’ Centre, Geology,
, 2008. Return to text.
- Explore The Giant’s Causeway, The National Trust, Saintfield, Northern Ireland, p. 6, 2002. Return to text.
- The lignite deposits do not represent a soil horizon. In soil, the decomposed organic material is finely dispersed. Return to text.