AbstractAn analysis of the preferred orientation of the long axes of erratics contained within the superficial deposits of the Lleyn Peninsula indicates that during the two recorded glacial advances the area was invaded by ice from two source regions—the Irish Sea ice‐sheet and local Welsh ice‐bodies. An attempt is made to re‐construct the pattern of ice movement during both glacial advances, to determine the extent to which ice from each source region penetrated Lleyn, and to interpret the environment under which the tills were de