Point Gratiot, a rocky headland in Dunkirk, New York, protrudes one kilometer into Lake Erie, one of the Laurentian Great Lakes. The point is underlain by the Upper Devonian Dunkirk Shale, a black shale deposited under anoxic conditions in the Appalachian Foreland Basin during the Acadian Orogeny. Here, the Dunkirk Shale is overlain by Pleistocene glacial deposits producing a disconformity that represents the loss of approximately 375 million years of Earth's history.
The eastern side of Point Gratiot (upper picture) is usually difficult to access. However, during fall 2020, a small beach formed at the base of the cliff enabling access. The shale clearly shows two sets of joints (stress release fractures) that are nearly perpendicular to each other.
The lower photo shows the disconformity between the Devonian shale and the Pleistocene glacial sediments. The top of the shale is marked with glacial striations and grooves accented by sand blown from the adjacent beach. This erosional surface is overlain by 10-20 cm of cobble-bearing glacial till deposited directly by the ice. Above the till is over one meter of well-sorted silt that displays spectacular contorted bedding. Contorted bedding results from the rapid dewatering of sediment as it compacts. This silt was deposited in the Pleistocene precursors of Lake Erie. Photos taken October 13, 2020.
Point Gratiot, New York Coordinates: 42.4882, -79.35304
Point Gratiot Light, is an active lighthouse located at Point Gratiot on Lake Erie in New York state.
The lighthouse was established in 1826 and the current tower was first lit in 1875. The lighthouse was automated in 1960 and is still operational. The foundation is made out of dressed stone and the lighthouse is made out of rubblestone encased in brick. The tower is square-shaped with the upper two thirds in white and the lower third left natural and the lantern housing in red. The original lens is a third order Fresnel lens installed in 1857 and is still in operation. Its being still in use makes it a rarity. Only 70 such lenses are operational in the United States, 16 being on the Great Lakes of which two are in New York. At the entrance to the park property is the South Buffalo North Side Light, formerly located in Buffalo Harbor. It was added to the National Register of Historic Places as Point Gratiot Lighthouse Complex in 1979.
The Dunkirk Lighthouse is open daily except Sunday. Guided tours include climb to the top of the lighthouse, Veteran museums and gift shop.
The Archives Center at the Smithsonian National Museum of American History has a collection (#1055) of souvenir postcards of lighthouses and has digitized 272 of these and made them available online. These include postcards of Dunkirk (Point Gratiot) Light with links to customized nautical charts provided by National Oceanographic and Atmospheric Administration.
