ABSTRACT

The Grimsby Sandstone (Lower Silurian) crops out parallel to the south shore of Lake Ontario from Clappison Corners, Ontario, on the west to Fulton, New York, on the east. It is dominantly a hematitic quartz sandstone with subordinate graywacke, siltstone, and shale. Sand grains are well rounded and are typically cemented with silica and sporadically with calcite. Red color dominates with some green-gray mottles and layers. Mechanical analysis of thin sections from samples at 15 measured sections showed increasing mean grain size from Clappison Comers, Ontario (0.0364 mm), east to Lockport, New York (0.1051 mm), and from there decreasing east to Fulton, New York (0.0652 mm). This corresponds directly to a thickening of the formation from 5 feet 4 inches at Clappison Corners to 74 feet at Lockport, thence a thinning to 7 feet 4 inches at Fulton.

Deltaic sub-aerial to near-shore environment of deposition is indicated by the gross lens shape of the formation, its red coloration, variable clastic lithology, current and interference ripple marks, shale pebble conglomerates, swash and wash marks, and mudcracks.