These two trolls first appeared as actors in Moving Pictures.
As far as their names go, Flint is obvious, but I had to look up Morraine: Webster spells it with one ‘r’, and defines it as “the debris of rocks, gravel, etc. left by a melting glacier”.
An email correspondent subsequently pointed out to me that Webster’s definition is lacking, because (a) the spelling with two r’s is valid, and (b) morraine is unstratified debris only. If it were stratified it would be called esker or kame, which are of course fluvioglacial products rather than just glacial.