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Niagara Escarpment

We are fortunate to have an exposed region of the Niagara Escarpment on the east side of the Cofrin Arboretum where the trail steps down from Bay Settlement Road and then runs along and below the cliff edge. The area was quarried and you can still see where piles of tailings were left and where slabs of limestone were cut from the cliffs.

The Niagara Escarpment is the edge of a thick series of dolomite layers of Silurian age stone that extends from Ontario into Wisconsin. The dolomite began to form over 400 million years ago in shallow seas as tiny aquatic organisms called foraminifera died and their calcium-carbonate shells piled up, forming sediment. Over time the calcium carbonate was converted to limestone or dolomite. Earlier and later, the sediment was mostly clay, and softer shales built up forming layers of soft over hard rock.

The escarpment forms because there are layers of hard rocks on top of soft rocks and the layers are tilted slightly, so the layers are exposed at the surface at an angle. The tops of the bluffs are mainly composed of layers of hard Silurian dolomite. Softer layers of Devonian and Ordivician rock composed of slates and other sedimentary rocks erode away under the bluff and on the sloping side to create the characteristic "cuesta" landform. One side of the cuesta is a steep escarpment of erosion resistant rock, while the other is has a longer gentle slope of more easily eroded rock. Glaciation and melt water significantly altered the original formation leading to the formation of a cuesta. When water undercuts the bluffs, erosion continues. Eventually the undercutting is severe enough that blocks of dolomite tumble down the escarpment forming piles of boulders. Today the Niagara Escarpment forms sharp 150 foot bluffs along the bay of Green Bay as it extends through Door County. The escarpment varies in profile forming a series of ledges, low cliffs and pavement including areas where the escarpment is completely buried.

Along the edge of the Niagara escarpment, a dense band of Eastern White Cedar (Thuja occidentalis) forms what may be the oldest forest ecosystem east of the Mississippi. Tree ring data indicates that some of these trees are over 900 years of age. Dense stands of cedar in combination with the limestone bedrock create unique reduced light conditions in the understory. Additionally, the lake climate, rock faces and crevices and the slumping bedrock create unique microenvironments that support a diversity of species, many of which are endemic to the area. For example, minute calcium loving land snails form highly diverse assemblages on the escarpment. Research by UWGB faculty and students have revealed that as many as 20 different snail species can be found in a meter square area of the escarpment. Increasing human pressure on escarpment habitats has threatened and endangered several species, including the federally endangered dwarf lake Iris (Iris lacustris) and the Hines Emerald dragonfly (Somatochlora hineana).

NAS emeritus professor Steve Dutch has a site detailing the geology of the escarpment.