A new interpretation of Silurian Lower Clinton relationships observed in the area between Medina, New York, and Clappison's Corners, Ontario, is presented. The Lower Clinton Group in this area is considered to include those units between the Thorold Sandstone and the Irondequoit Limestone. The profound lithological and faunal differences between the Lower Clinton strata of western New York and those of the Niagara Peninsula in Ontario are probably the result of deposition in a shallow basin under conditions controlled by proximity to the Cataract shelf (Bolton, 1957). The influence of this shelf extended south and east of Hamilton, Ontario; its effect was felt at the beginning of Early Clinton time. Frequent slight changes in the elevation of the shelf area and the nearby depositional basin to the south and east resulted in fluctuations in strand lines and reworking and removal of some units. Supporting evidence includes thin conglomerates at several contacts, wedging out or overlap of lithologic units, and changes in fauna of successive units.

The Reynales Formation between Medina, New York, and Clappison's Corners, Ontario, is restricted and redefined to include only the lower, fossiliferous, limestone units which are here designated the Hickory Corners Limestone Member (new name) and the Merritton Limestone Member (new name). The upper more dolomitic and less fossiliferous unit, herein named the Rockway Dolomite Member (new name), is removed from the Reynales and is considered to be the lower member of the Upper Clinton Irondequoit Limestone.

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