This is not a green man, that's something quite different. This is not on a mountain, even by the somewhat modest English definition of 'mountain'.

The south-eastern part of England lies on deep chalk beds. These form the 'white cliffs of Dover' and extend northwards to East Anglia and west to Dorset. The chalk forms 'downland', gently rolling terrain often covered by short grass. If you dig a short way under the grass you'll find bright white chalk. This has been used to make large drawings on the sides of the downs. Most of these are 'white horses'.

Do read the linked article on the Yahoo page, it gives a bit of background on the Cerne Abbas Giant, but their date is suspect - 200 AD seems more credible, and their picture seems a little odd too. A quick Google search turned up several more credible images of the Giant in his, er, unprotected, state.

This is not the first time that this monument has been embellished like this.

It is extraordinary that an image with such striking sexuality has survived in an England that has been absolutely paranoid about such images over the last several hundred years.

LOL

When we were in the UK a few years ago we made a special trip to see this. Some of the research done on the figure has shown that at one point he may have been holding a spear in the other hand. The Romans stationed there at the time may have modeled him to resemble Hercules.