How entrainment happens

This diagram shows a particular set of glaciological circumstance that would explain why the bulk of erratics entrained into the Irish Sea Glacier appear to have been "plucked up" and carried off in the body of the glacier from the northern flanks of the Preseli hills (both the main ridge and Carningli-Dinas Mountain).

Richard Bevins is searching for other rhyolite outcrops that might match with rhyolite fragments found at Stonehenge -- I wouldn't mind betting that another source area will be found in or near Tycanol Woods..........