Devils Tower, the Hill of Allen, the Valley Park and Close Encounters of the Third Kind

Devil's Tower in Wyoming. Ben Stephenson from Cleveland, OH, CC BY 2.0 , via Wikimedia Commons

If you were watching Close Encounters of the Third Kind this afternoon (I hadn't seen it for maybe 15 years), you would have seen the towering rock formation that's used as a plot device and features in the end of the movie when the huge spaceship appears and the aliens emerge. This is Devils Tower in Wyoming, classed as a butte and possibly a laccolithic formation, composed of igneous rock. A butte is an isolated hill with steep, often vertical sides and a flat top. Igneous rock began as molten rock or magma that originated from inside the Earth, and then cooled. Examples are granite (which forms the Wicklow Mountains) and basalt (The Giant's Causeway). A laccolith is a body of molten rock that pushed up through layers or strata of softer rock such as sandstone, but didn't emerge as a volcano. Over hundreds of millions of years, the softer rock eroded away to leave the harder and steep sided tube. In Ireland we have several features on the landscape that would originally have been volcanoes. They include the Hill of Allen (what's left of it) and Croghan Hill near Daingean in Offaly. As far as I know, Andesite, the hard rock from Roadstone's Allen quarry was used for the walls and stone landscaping around St Brigid's Well in the Valley Park. Maybe someone can clarify this?