In the
Illinois Basin,
Michigan Basin and Cincinnati Arch the Trenton Limestone is classified as a
geological formation rather than a group. In the
Appalachian Basin the Trenton Group is broken down into formations and members.
Glens Falls Limestone The
Glens Falls Limestone contains thin fossiliferous beds. The inclusion of ripple marks indicates this formation was deposited in a shallow marine environment. The Glens Falls contains two members, the upper member is the Shoreham and the lower Larrabee Member. The upper member contains more clay and silica where the lower member contains more carbonate material. Both are named for separate quarries located in
Vermont Napanee Limestone The Napanee is a thin bedded deep water limestone. The formation is composed of thin interbedded
wackestone and
shale. This formation can be organic rich in parts and sub surface is dark grey to blackish, while at surface it will weather to a tan or buff color. Fossils can be abundant including
bryozoans, brachiopods, crinoids,
trilobites, and other mollusks.
Dalmanella rogata is rather common.
Selby Limestone The Selby is primarily composed of a nodular dark grey
packstone and
grainstone with
bioclast inclusions. It is massively bedded. In outcrops found in New York the Selby is about ten feet thick. The Selby and the Watertown Formation below, mark a change from the back reef facies of the
Black River Group to an off shore ramp. Fossils found within the Selby include
corals,
orthocones, various types of
brachiopods,
stromatoporoids green algae, including
Receptaculites and a small amount of
crinoids. == See also ==