What is on these rafters?

[montana]

Felt like I was standing on my head. House built in 1960. Old 2x4 rafters with what looks like black tar used to cement a silvery rolled roofing on the underside of the roof. But the black ooozy tar compound looks like it dripped UPWARD. I would almost think that the the rafters were originally used somewhere else lying down, and then flipped upside down and re-claimed as rafters. Any other ideas? I was stumped. Oh, don't worry about all the brown mold, that is a side issue to my question here.

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[Neal Lewis]

That house is much older than 1960.

[John Kogel]

Recycled lumber. I see the tar turned around on one piece and is now dripping down. All is well with the world. []