[citation needed][1] In upstate New York and the Niagara peninsula of southern Ontario the sedimentary rocks tend to dip downward in a generally a South direction.

[2] Northwest of Ingersol and Woodstock, across the crest of the Algonquin Arch, the band of outcrop turns more northerly, and strikes north-northwest for about 140 km to the east shore of Lake Huron in the Kincardine area (as shown in the map on the right).

These rocks continue northwestwards under Lake Huron, and reappear in the northern part of the southern peninsula of Michigan, north of Alpina[3] (as shown in the map on the right).

This variety of chert was of great importance to First Nations peoples throughout Southern Ontario, who used it to make stone tools (lithics) such as projectile points and hide scrapers.

This wide distribution implies either a very large seasonal migration of ancient peoples or long-distance trade routes, with both likely being the case at different times throughout the prehistory of the Great Lakes region.

In descending order:[8] The Seneca and Moorehouse members are sharply divided by the Tioga-B Bentonite layer, which was formed in a very short time period as the result of a large volcanic eruption in what is now the state of Virginia.