The Origins of Andesite

The primitive andesitic hand axes (called bifaces) such as those from the Bytham River gravels at Brooksby in Leicestershire are made from andesitic tuff, a kind of volcanic rock found only in the Lake District and North Wales.  Archaeologists speculate that hominins (early humans) may have carried such tools for a considerable while before they were lost or discarded - so they may have been brought into the region by nomadic groups from further north.  However, andesitic boulders are occasionally found in the river gravels of the Midlands, having arrived through natural processes of erosion and deposition associated with glaciation, and so it is not impossible that some of the hand axes may have been made locally from such material.  You can read more in John McNabb's authoritative The British Lower Palaeolithic: Stones in Contention.