These fossils came from Mississippian rocks from eastern Nevada and are 330 million years old.
They were originally laid down in sand and gravel in a river delta where logs of trees of the time were deposited, buried and later fossilized. These included giant horsetail rushes, scale trees and tree ferns.
There are samples here of bark and branches. The scales are the scars left by the “leaves” when they fell off, much like leaf scars on a pineapple. Also seen are elongated scale tree “leaf” scars made as the scales stretch as the lower portion of the trunk continues to grow. The roots and rootlets of the scale tree were originally classified as a different genera of tree until the whole tree was found. They still go by a different name, Stigmaria. Sphenophyls fossils are the whorls of “leaves” that form at nodes on the stem of the plant.
Also in the display are samples of bark and branches of giant extinct horsetails. Calamites are members of Sphenophyta, a division of primitive spore-bearing vascular plants. These were tree sized relatives of the living species - Horsetail (Equisetum). They were up to 3 feet in diameter and 100 feet tall. Their leaves were arranged in whorls like spokes at regular intervals along the jointed and often ribbed stems.
The reproductive structures consist of greatly compressed stems called strobili or cones, which formed at the ends of the branches. These extinct trees contributed to the coal beds of the Carboniferous Period, 360 to 286 million years ago. Horsetails of today are sometimes called “scouring rush.” The Forty-niners scoured their pots and pans with the horsetails because they incorporate quartz crystals in their tissue and are very abrasive. Another mineral known to accumulate in the walls of their cells is minute amounts of gold.