I have a Marlin 60, but I'm not terribly familiar with its brothers and cousins. The "hook" (if we're referring to the same projection sticking out horizontally from the bolt itself) - aka "charging handle" on my Model 60 pushes straight into the bolt once the bolt is pulled fully to the rear, thus locking the bolt in that position for cleaning, etc. When the bolt is forward, it does not move appreciably, and would give the impression that it's fixed. It does not, if I recall, hold the bolt open after the last round is fired as apparently do the post-1985 Marlin semi-autos. It may be that your rifle was manufactured before either the manual bolt hold-open or the last round hold-open was included as a feature.