Named for Cataract, Ontario, CAN. Fifty feet of rocks previously assigned to Medina formation at Niagara Falls, NY, reassigned to Cataract formation. Occurs from Niagara Falls to Manitoulin Islands in Lake Huron. At Manitoulin Islands, lower 45 ft consists of thin-bedded magnesian limestone; upper 65 ft consists of red, nonfossiliferous shales. Thickness is 82 ft at Cataract, where it also fossiliferous. Age is Silurian.

Source: GNU records (USGS DDS-6; Reston GNULEX).

In 1913 (Ottawa Nat., v. 27, p. 37-38) M.Y. Williams divided Cataract formation of Georgian Bay region into Kagawong member above and Manitoulin member below, while A.W. Grabau (GSA Bull., v. 24, p. 438, 460, 1913) divided the same beds into Cabots Head beds above and Keppel dolomites below, the latter resting, with probable disconformity, on Queenston shale.
In 1914 (Sci., n.s., v. 39, June 19, p. 915-918) E.M. Kindle recommended the following names for subdivisions of Medina formation (restricted), in descending order: Thorold sandstone, Grimsby sandstone, Cabot Head shale, Manitoulin beds, and Whirlpool sandstone.
In 1914 (GSA Bull., v. 25, Sept. 1, p. 277-320) C. Schuchert divided Cataract formation of Ontario into (descending): (1) Cabots Head shale member (20 to 75 feet of greenish somewhat calcareous shales with occasional thin beds of magnesium limestone); (2) Manitoulin limestone member (9 to 60 feet of heavy-bedded magnesium limestones, with local reefs of corals and bryozoans, and, to south, thin beds of sandstone); and (3) Whirlpool sandstone member (0 to 22 feet of coarse, cross-bedded, white, red, or mottled sandstone, extending from Lockport, New York, to near Collingwood, Ontario). He stated that all of these members are present at Cataract, Ontario, but he did not apply Cabots Head and Manitoulin in Niagara Gorge section, where he described Cataract formation as consisting of (descending): (1) Dark green shales, 6 feet; (2) thin-bedded green sandstone underlain by yellowish magnesian and argillaceous limestone with small black shale pebbles, 5 feet; (3) green shales, 10 feet; (4) dark-green shales with very thin-bedded argillaceous magnesian limestones, 5 feet; (5) dark green fissile shales, 7 feet; and (6) Whirlpool sandstone member, 22 feet. The beds resting on Cataract formation in Niagara Gorge he called Medina formation [a greatly restricted use of Medina] and described them as consisting of (descending): (1) Thorold [sandstone] member, 8 feet thick; (2) 15 feet of red and greenish gray, much cross-bedded and channeled sandstone with very little shale; (3) thin-bedded red sandstones, with considerable red shales and two or more zones of localized storm-rolled mud balls, 35 to 40 feet; (4) gray sandstone with shale partings, 5 feet. He stated that the Medina is of the Appalachian province, while the Cataract is of either the St. Lawrence or the Arctic realm; that the Cataract wedges in below Upper Medina in Niagara Gorge; that the Medina [restricted to uppermost 60 or 65 feet of original Medina] thins out to northwest, so that Cataract thickens in opposite direction; that the Medina [restricted], Brassfield, and Cataract "are correlates of one another," but that "they represent three physical provinces and marine basins," and that the 3 names "should be retained as names for independent marine faunas and formations." The same year (Canada Geol. Survey Summ. Rpt. for 1913, p. 179-188, 1914) M.Y. Williams adopted Grabau's name Cabot Head shale to replace Kagawong (preoccupied) and introduced Grimsby sandstones for 0 to 50 feet of beds underlying Thorold sandstone and overlying Cabot Head shale, and also overlying Cataract formation of Schuchert; he also used Manitoulin member and Whirlpool sandstone for the rocks underlying Cabot Head shale. His 1919 classification (Canada Geol. Survey Mem. 111, No. 91 of geol. ser.) employed the same names as his 1914 classification. he called the beds Medina-Cataract; stated that they are contemporaneous with Medina; that Schuchert restricted Medina to Grimsby and Thorold sandstones and called the underlying beds Cataract formation, that he (Williams) considered the Grimsby and Thorold are "only facies of the top of Cabot Head shale, although they represent another faunal invasion"; and that name Cataract is necessary as the phases of sedimentation are very different from most of the Medina. He also introduced two new names for dolomite beds in Cabot Head shale member of Bruce Peninsula and Manitoulin Island, the type locality, using St. Edward dolomite lentille for a bed near top of Cabot Head shale, and Dyer Bay dolomite lentille for a bed in lower part of upper half of Cabot Head shale.
In 1918 (GSA Bull., v. 29, p. 332, 364) G.H. Chadwick applied Cataract formation to beds between Grimsby sandstone above and Whirlpool sandstone below.
In 1923 (Maryland Geol. Survey Silurian vol., p. 334-336) E.O. Ulrich stated that fauna of Dyer Bay dolomite is Niagaran (middle Clinton), and not Medinan, and he restricted (p. 267) Cataract to pre-Dyer beds of upper Medinan age, including Grimsby sandstone in Medinan, and transferred Thorold sandstone to Clinton.
In 1924 (Canada Dept. Mines, Geol. Survey Mem. 138) A.F. Foerste used Grabau's restricted Medina "to include the beds above the Queenston and below the Clinton," and stated that upper part of Cataract formation in southern Ontario is formed by Thorold sandstone member and Grimsby sandstone member, and that Whirlpool sandstone member is base of Cataract formation from Niagara River to vicinity of Duntroon, about 8 miles south of Collingwood, Ontario.

Source: US geologic names lexicon (USGS Bull. 896, p. 369-370).