There may be a lot of people employed in gravel extraction in Spelthorne for all I know, but some decades ago there were far, far more men employed in extracting and processing materials (I hesitate to use the word minerals) from Surrey, especially in the east. Forget the few ancient underground sites - look at the surface pits - sand, fullers earth, chalk, clay - all major industrial activities in the area, all of which would have been recorded in national statistics. Stuff and nonsense? Were these gravel workers or administrative mining company employees making it up on the recent census, then? It's an odd title for the thread, I have to say.