Answer:
Goes over all the hills and hollows. Bites hard, but never swallows.
The ones who see it may go blind, Contracting the fool's madness. You have to dig to find it, Crush big stones or mine it. Wash dirt clumps in a pan and wait for it to settle, A shiny, precious metal.
What is bought by the yard by is worn by the foot?
They have not flesh, nor feathers, nor scales, nor bone. Yet they have fingers and thumbs of their own. What are they?
The older they are the less wrinkles they have.
If it’s information you seek, come and see me. If it’s pairs of letters you need, I have consecutively three. What am I?