The Interbasaltic Bed at Giants Causeway, Northern Ireland

It’s not soil layers

by Tas Walker

Red Interbasaltic bed forms a prominent feature around the Causeway cliffs, Northern Ireland. Close up the Interbasaltic bed shows it’s just an altered, friable horizon—not soil.

One striking feature of the Causeway cliffs, Northern Ireland, is an orange bed, which 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 Interbasaltic Bed is a thick soil that formed by weathering over an unimaginably long time. For example, the website of the Giants 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

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

• Long-term weathering would not produce a soil bed with such an even thickness.

• Where the bed slopes down near Giants 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.

The bed does not represent a long period of time but rapid burial and energetic chemical alteration because of the heat. When it is interpreted within a biblical Flood framework the Interbasaltic Bed makes good sense.

The timing of Giants Causeway within the biblical geological model.

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References

1. Wilson, H.E., Regional Geology of Northern Ireland, Geological Survey of Northern Ireland, Belfast, pp. 63–64, plate 9B, 1972.

2. Lyle, P., A Geological Excursion Guide to The Causeway Coast, W&G Baird, Antrim, Northern Ireland, pp. 24–25, 1998.

3. Giants Causeway Visitors’ Centre, Geology, accessed 6 May 2008.

4. Explore The Giants Causeway, The National Trust, Saintfield, Northern Ireland, p. 6, 2002.

5. The lignite deposits do not represent a soil horizon. In soil, the decomposed organic material is finely dispersed.

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