Shiny things

Trying to think what this rock could be - a buried standing stone? A cliff face? How did it get here?
So the story. Daughter and I are having a boardwalk constructed, so that we can get across out boggy wetland and down to the pond in the lower ground. It zig zags down the ravine through the woodland first. ( this is because I am not far off needing a wheelchair). Bloke doing the work had to use a digger. He came across a massive rock, which was in the way of the boardwalk, so with a lot of effort tried to drag the rock to one side. The top of the rock sheered off, leaving the rest of it buried in the ground, the surface of which was flat (as was the bottom of the bit that had scheered off, which by the way is a good 6 foot by 4 foot and 3 foot tall approx.

The ravine and where it flattens out onto the lower ground was in it's past a large river, but when the pond was being dug solid ground was reach, which could not be dug through and the ground was totally dry, this expalined why the water just laid on the top causing bog/and wetland. I had a rock found here analised and it turned out to be fossils of Trilobites.Trilobites were small woodlouse looking creatures that inhabited the ocean floor.

Which brings up the question,is the rock part of once a cliff face? But there is only one visible of this size. Yes there are a huge number of very large rocks with amazing foramtions. It's side are so flat I wonder if some ancient standing stone? I will probably never know the answer but it is interesting

Massive Split rock by Helen Skelton, on Flickr