Answer:
Lighter than what I am made of, More of me is hidden Than is seen.
I have legs but walk not, a strong back but work not. Two good arms but reach not. A seat but sit and tarry not.
Salty water everywhere but not sea in sight.
Black we are and much admired. Many seek us if they are tired. We tire the horse, and comfort man, and turn White when we've fulfilled your plan.
A muttered rumble was heard from the pen, and I, in my walking stopped to look in. What was this I saw? A massive beast, hoofed, and jawed. With spikes upon its mighty brow, I watched as he struck the turf and prowled. And yet for all of his magnificence, he couldn't get out of that wooden fence.
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.