Wednesday, April 5, 2017

Don Robinson on the Rocks

Hiked this morning at Don Robinson State Park, with all its raw-looking, yellow-orange must-be-iron-in-there sandstone rock cuts. I'd taken some wildflower photos and then propped myself up to rest against a rock cut that exposed alternating layers of sandstone and limestone, like cake, and saw some of the yellow rocks freckled with black.

Closer inspection showed the freckles to be what looked like tiny plant fossils. (Photographed with a magnifying lens; actual size, 3cm.) Amazed and excited, I looked harder. Most of these enchanting fernlike things were pressed into a single layer of the rock. Five miles away at my place we don't have this type of sandstone and we don't have these.
The dark lines like black pepper are the "fossil" layers.
But, surprise--they are not plants! They are dendrites, deposits of manganese oxide, that have fooled a whole bunch of people, including me now, into thinking they are plant fossils. Internet says, "They form as water rich in manganese and iron flows along tiny cracks between layers of limestone and other rock types." I don't know about the manganese, but the rock there has iron and limestone, so if this is Wednesday it must be dendrites.

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