NHER 45505 (Find Spot record) - Large lava stone blocks, Garden of 14 Hardingham Road

Trawled up from the North Sea at unknown location and placed in garden.
Two blocks of volcanic lava; one approx 4 ft square and 2 ft thick; the other 5 ft long by 2 ft square with shaped or chamfered edge. Heavily incrusted in places with marine organisms.
No instances known of importation of Roman or medieval date of lava of that size. Are these modern shipwreck losses? Is the lava from Norway?
E. Rose (NLA), 24 August 2006.