One I missed in my days as a Mining Geology student. There is a minor zinc and copper deposit in the hills between Cardiff and Caerphilly (Cefn Carnau?) Some fellow students and I did a geochemical analysis one year. Another group got to try seismic surveys.

The crude way to do this is to place a line of microphones in the ground, with a spare manhole cover (I've no idea where they nicked obtained this from) at one end. Whack the manhole cover with a sledgehammer. Look for the echoes in the recorded trace from each microphone, extrapolate into bedding and faults under the test area.

The first results they got were too faint to allow proper analysis, even with the brawniest or most psychopathic students wielding the hammer. So, on a subsequent day, they tried for more oomph by placing a charge derived from a shotgun cartridge in the middle of the manhole cover. The results weren't any better; the official explanation was high-frequency harmonics obscuring returns (or in other words, the blast caused the manhole cover to ring like a bell).

The manhole cover survived, by the way, as did the students. Well done messrs. Stanton of Stavely.