dinosaur bone

I found a small collection of very old bones and some fossils while clearing an estate in Seattle, Wa. Please help me identify what this bone is from. I will post some of the other items I found in another post here. I would like to find out how old it may be and what type of animal or...

My best guess is an agate forming around a bone The outside is hard but the white rock/substance that the rock seems to be forming over is soft