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Shelfstone is a ledge or projection extending from the edge of a cave pool or sometimes attached to a speleothem that has been submerged in a cave pool after its formation in air, or as a small island in the pool in what is sometimes called a lilypad (photo #2). Typically they may ring the entire edge of a pool basin, as in photo #1. It is almost always formed from calcite, when material precipitated on top of a cave pool (often rafts) attach to the side, and deposition continues to add growth laterally and underneath. As such, they are indicators of past pool levels. Shelfstone may be quite thick when a pool has stayed at the same level for a long time (as seen in photos 1, 3, 4, and 5), or thin and delicate (as in the second photo).

Shelfstone may acrete as a ring around the base of a stalactite that has become inundated by a standing pool, creating what is sometimes called a lily-pad shelfstone and by some authors, stalactoflats (photo #6).

In photo #7 we see an unusual set of shelfstone tiers above a pool in a cave in Spain. To form this, the lake must have changed level periodically but maintained those levels for long enough periods for the shelfstone to accrete. The author has only seen such flowstone tiers is a few caves, but this one in Spain is the most remarkable example of them all.

AUTHOR: Dave Bunnell