While in the North Dakota Badlands I found a hollow in a hill with what appears to be to me a bone. It is encased in sandstone about 20 feet below the top of the hill and 15 feet into the side of the hill. The piece that was exposed to air was soft and appeared to have a silver colored center where marrow may have been. I have chipped away about 8 inches of sandstone and it seems to be thicker and no longer soft. It seems to be light brown and of unknown length or size. Who would I send a sample to that could verify if this is a bone of some sort, and possibly how old a bone?

Do not try to get a sample. The item has much more value (scientific) as a whole. If it were me I would expose as much of it as possible without breaking it, take plenty of pictures, and send them to the nearest University Paleontology department for identification and information.