November 7, 2017
I tagged this photograph with “lichen,” but I’m not really certain that the white marks on the large rock are lichens. What else could they be? Fossils in the stone?
Later in the Day
Scientist-husband David suggests “mineralized inclusions in the rock. Could be of biological or abiotic origin from what little I can see.”
We now have two more opinions favoring the lichen theory: One is from my husband’s colleague in the Oberlin College Department of Biology, and one is from Art Murphy, who usually knows a fossil when he sees one. (See Art and Fossils.)
April 19, 2015
August 27, 2012
Saturday was another day of sunshine and low water in the river. We’ve had enough rain lately that many of the rocks along the river have sprouted moss. Algae are more prevalent, too. And still—I assume because we’ve also had extended days of heat and sunshine—the iron bacteria have been visibly at work. Trees or their shadows overhang the shore on the “other” side of the river, where I took these photographs. So in the second photograph you see a lot of shade with the sun barely illuminating an area of wet shale covered with algae. The rust colors are the result of the bacteria having deposited iron oxide on the shale and algae. What you see in the third photo is what happens when a shaft of sunlight strikes a leaf (sycamore?) in a few inches of water populated by algae (and probably cyanobacteria, the dark blue-green color), some of which has been layered with iron oxide by the iron bacteria.