Corkscrew Mystery Uncorked

For one of geology's oddest puzzles an odd solution was last week suggested. The puzzle was the origin of "devil's corkscrews," which are fossils six to eight feet high, spiral in shape, with whorls eight inches to three feet in diameter. Buried vertically, they are found in Nebraska's Sioux County in Miocene deposits 15-to 30,000,000 years old. Moreover, fossil beavers have been found in several of the fossil corkscrews, in which microscopic study shows an abundance of petrified plant cells. So two theories arose:

1) the corkscrews are petrified liana (woody, rope-like) vines which twisted naturally in ancient tropical Nebraska;

2) the corkscrews are the petrified debris which filled the downward spiraling burrows of beavers.

Both theories were reconciled convincingly last week by Alvin Leonard Lugn of the University of Nebraska. In the Journal of Geology he explained that the vines grew in spirals and were buried naturally amid pulpy swamp vegetation and sands. Then the beavers came and dug out the rotting material inside the corkscrews to make burrows with "prefabricated" walls.

This explains why beavers of later ages did not also live in corkscrew nests. They did not lose the art; the convenient lianas just disappeared as Nebraska cooled off.

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