Some Eocene silicified wood from the Yellowstone "fossil forests" is riddled with small diameter holes previously presumed to have been excavated by wood-boring insects. The holes occur only near the surface of the wood. Thin section analysis reveals isolated groups of calcified cells in otherwise silicified wood. Recent differential weathering of calcite with respect to silica produced the holes or pseudoborings on exposed surfaces. The apparent replacement of calcite by silica and the excellent preservation of fine structures may bear on proposed Tertiary climatic changes and rate of petrification.--Modified journal abstract.

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