for instance , i do not know what linguistic complications were introduced , or may be thought to have been introduced , by the ' belgic ' invasion , interrupted by julius caesar 's ill-considered and deservedly ill-fated incursion ; but they could , i suppose , have involved dialectal differences within celtic as considerable as those which divided ninth-century norse from the older germanic layer which we now call 'anglo-saxon ' but 2 , 000 years hence those differences which now appear marked and important to english philologists may be insignificant or unrecognizable .