"The earliest materials present are the microliths and microburin from Interventions 5 and 8. These geometric forms all date to the later Mesolithic period. One of the microliths , from Intervention 5, is a narrow blade, retouched on both sides. It is narrow and almost rod-like suggesting a date of the very later or terminal Mesolithic. The contexts from which the microliths were recovered suggest that all these finds are residual."

What does residual mean in this context?

Interesting stuff, Small Blue Planet, thanks

Treeman