Every whinstone boulder i checked attracted a magnet, this stretch of Marton west beck has a very large amount of whinstone of all sizes, all seem to be water worn, and all the Andesite (whinstone) i tested was magnetic.
Ime not sure what rock this is yet, but it came from the same gravel layer as the magnetic Andesite (whinstone)
These images show what i believe is the same red clay ive found underlying everything in the south west Middlesbrough area, with the gravel layer above.
The image below hopefully shows the amount of material above these layers, i would say at least a 35 metres