Took a few moments but I found your video.http://www.youtube.com/watch?v=E7gSMa1_F-Q
Take a look at this web site http://en.wikipedia.org/wiki/Round_shot
Round shot (or solid shot, or a cannonball, or simply ball) is a solid projectile without explosive charge, fired from a cannon. As the name implies, round shot is spherical; its diameter is slightly less than the bore of the gun it is fired from.
Round shot was made in early times from dressed stone, but by the 17th century, from iron. It was used as the most accurate projectile that could be fired by a smoothbore cannon, used to batter the wooden hulls of opposing ships, fortifications, or fixed emplacements, and as a long-range anti-personnel weapon.
In the photo which accompanies the link you will see a selection of cannon balls including a couple of stone balls. These were recovered from the wreck of The Mary Rose sunk in 1545. Clicking on the picture will bring you an enlarged view. It is too large to fit on this board.
If you concentrate on the two stone balls on top you will see striations similar to the grooves on your stone ball. This would have been part of the smoothing process so that the ball would fit inside the bore of the cannon.
That would be my best guess. Judging from the size it looks like an artillery unit was running low on ammo and decided to make a few spares just in case.
Something is wrong here. War, disease, death, destruction, hunger, filth, poverty, torture, crime, corruption, and the Ice Capades. Something is definitely wrong. This is not good work. If this is the best God can do, I am not impressed.
-- George Carlin