I found my marbles !

Dim memories of primary school came back - "Do you want a game of Stankie?" or "Skyscrapers?". The former involved trying to hit your opponent's marble by shoving it round the uneven surface of a drain cover ("stank") whilst the latter involved trying to hit your opponent's marble by dropping it from the tip of your nose whilst standing up.

So just as I'm losing my marbles, I found them again.