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The transition from
the Fountain Formation into the overlying Lyons Sandstone is marked by a
fairly abrupt change from feldspar-rich fluvial (river-deposited) sandstone
beds to quartz-rich, windblown, fossilized sand dunes. Frequently you can
see spectacular bedding features in the rock, representing the fossil sand
dune. You may discover the trackways of small amphibians or even the fossil
impressions of raindrops preserved on the solidified sandy surfaces. The
sand dunes existed during the Permian. The Lyons Sandstone ranges from about
100 to 200 feet in thickness. It is named after the town of Lyons north
of Boulder, where you can purchase slabs of ancient dunes for building walls
and as ornamental rock. Look for good exposures of these sandstone beds
at many of the parks and open-space areas near Lyons. |
