This slab is a two for one in terms of species present. It has an example of
Rafinesquina alternata as well as
Sowerbyella sericea. It's from the Collingswood member of the Whitby formation. These are both uncommon fossils to find in the Collingswood member and could be washed in from another location by a storm as black shales generally represent anoxic, deeper water conditions.
Overview of the slab
Rafinesquina alternata
Sowerbyella sericea
The Whitby formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These
fossils were collected from the St. Mary's Limestone Quarry in
Bowmanville, Ontario. I used William Hessin's book "South Central
Ontario Fossils", 2009, Self Published, pg. 125-126, 128 to help identify these
fossils.
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