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The Little Falls formation (sometimes referred to as the Little Falls Dolostone) is a Cambrian rock unit of New York State.

Occurrence
The type section of the Little Falls Formation occurs in the Little Falls Quadrangle, near Little Falls, NY. Here it lies unconformably on the Precambrian Grenville complex. The main outcrop belt of the Little Falls Formation extends roughly from the village of Poland, NY in the west to Randall, NY in the east.

Description
Dolomite is the predominant lithology, subordinated by sandstone and mixed sandstone-dolostone. Medium and thick bedding are characteristic of the Little Falls. At the occurence of its type section in the Mohawk Valley, the Little Falls is approximately 400ft (122 m) thick, and thins northward from the Mohawk Valley as a result of early Ordovician erosion. Dolomite is the dominant mineral in the Little Falls, and is a replacement after the original carbonate precusor minerals; there is also significant void-filling dolomite. Quartz is present as detrital grains and secondary overgrowths. Potassium feldspar (perthite and microcline) and calcite are widespread but not common; interstitial glauconite, hematite, and pyrite are also notable. Chertification both preceeded and followed dolomitization. Maturation of hydrocarbons to anthraxolite paragenetically overlapped the growth of secondary dolomite rhombs and quartz crystals in vugs. Replacement dolomite is generally coarsely crystalline (averaging 110 to 120 micrometers) and there are a significant amount of very large crystals that show undulatory extinction and low ferrous iron content.

Sub-Divisions
In his landmark 1981 work on the Little Falls, (see references) Zenger sub-divided the Little Falls Formation into 4 informal units. The lowermost unit, or "A," lies unconformably on the underlying Proterozoic gneiss. It is 90 to 100 feet (28 to 30 m) thick and consists of thin basal conglomerates and sandstones overlain by generally coarsely crystalline dolostones. Unit "B" is ~200ft (61 m) thick, and is made up of dark, fine- to medium-crystalline dolostone - many of the dolostone beds are vuggy. Within Unit "B" is a unique sequence of alternating algal stromatolitic dolostone and sandstone. The stromatolites are hemispherical, and consist of dark-grey to dark brownish-grey and light brownish-grey, very fine- to fine-crystalline dolostone. Unit B makes up about 1/2 of the total thickness of the Little Falls. Unit "C" is 45 to 70ft (13.7 to 21.3 m) thick, and is primarily coarsely crystalline, glauconitic dolostone with quartzose intercalations. Unit C is primarily olive-grey or light-grey, and ranges in grain size from medium to coarse. Unit "D," characterized by fine crystalline, laminated dolostone, is 30 to 70ft (9.1 to 21.3 m) thick, and contains reddish-grey zones and silicified ooids; according to Zenger, this unit is overlain unconformably by the Tribes Hill Formation in the Mohawk Valley.

In northern Washington County, NY, the Little Falls contains lenses of un-dolomitized, fossiliferous limestone. One such unit, lies 12 meters from the top of the Little Falls in northern Washington County. These lenses of limestone have been named the Rathbunville School Limestone. The lenses grade horizontally into dolomite, believed to be the result of hydrothermal dolomitization during the Taconic Orogeny. The Rathbunville School Limestone contains shelled macrofauna such as gastropods, cephalopods, orthid brachiopods, and trilobites. Based on the success of several recovery methods, Landing and Kröger concluded that faunal abundance and diversity were not originally high.

Depositional Environment
The original sediments that make up the Little Falls accumulated along the inner edge of a wide shelf that lay to the west of the slope into the Proto-Atlantic Ocean. However, dolomitization and poor lateral continuity of exposure make environmental interpretation difficult. Features such as domal algal stromatolites, invertebrate fossils, algal boundstones, burrowing and bioturbation, intraclasts, peloids, ooids, cross-stratification, ripple marks, channeling, dessication cracks, quartz sand grains, grain-supported textures, and dolostone textures are present. Each stratigraphic unit displays a variety of subtidal and pertidal characteristics; Zenger concluded that the depositonal environment of the Little Falls was an inner shelf area affected by tides. Zenger interpreted the origin of eolian-transported sand grains as another indicator of a tidal environment. Based on their research, Landing and Kröger concluded that the depositional environment of the Little Falls was a shallow subtidal, well-oxygenated, but restricted marine depositional environment, corroborating and expanding on Zenger's observations.

Mineralogy
The Little Falls Formation is famous for its diverse array of minerals and has produced a number of high-quality specimens. The Little Falls Formation is, in some of its cavaties (vugs) host to large crystals of pyrite, calcite, dolomite, and quartz, (notably Herkimer Diamonds) as well as other minerals<ref name=undefined.