The geologist David Webster, who lives at the old crofting village of Conisby on the hill above Bruichladdich, visited the site of our new warehouse development at Coultorsay earlier today. David is interested in examining the rock formations and types that have been exposed by the excavations that are preparing for the new buildings and their access road.
David is co-author of a new book “A Guide to the Geology of Islay”, which describes twelve walks on the island from a geological perspective. His partners in the book project were Dr Alasdair Skelton of the University of Stockholm, and Dr Roger Anderton who lives in Lochgilphead following a career in the British Geological Survey, Strathclyde University and the oil industry.
David showed how the underlying bedrock immediately encountered beneath the soil on the site is a ‘laminated meta-siltstone’, which in turn sits on layers of sandstone. David says the siltstone dates to around 700 million years ago, before the explosion of life on earth, and therefore pre-dates significant fossils. Veins of quartz are intrusive into the rock, which was formed during the build-up of sediments on an ocean floor before becoming ‘metamorphic’ through being subjected to pressure and heat.
Overlaying the siltstone is a layer of boulder clay that was deposited as layers of ice hundreds of metres thick melted after the last ice age. The advance of the ice will have scraped the land clean before finally dumping this thick layer of relatively infertile, clay-based brown soil all over everything as it melted a mere ten thousand years or so ago.
David is hoping to make further visits to the site and write a geological overview for us in the weeks to come.
Many thanks to the team from ISG for their assistance with access as always.