Quaternary glaciations in the Northern hemisphere : report no 6 on the session in Ostrava, August 16-25, 1979 : Project 73/1/24 / editors Vladimir Sibrava and F.W. Shotton ; [for the] IUGS-UNESCO International geological correlation programme ; edited in collaboration with the International Union for Quaternary research, INQUA / Prague : Geological Survey , 1981