NATURAL HISTORY, TORONTO REGION
The Silurian (Upper Silurian) of southwestern Ontario includes a number of fairly distinct subdivisions which have been classed in various ways, the Niagara Limestone standing out most prominently at the crest of the escarpment before mentioned.
Professor Parks gives the following classification of the Silurian :
Salina Impure limestone and shale with gyp-sum and rock salt. Guelph .... Dolomite.
Niagara Lockport—Dolomitic limestone.
Rochester—Shale. Clinton . . . . Limestone and shale. Medina .... Sandstone and shale. Cataract . . . Sandstone, etc.
All of these subdivisions except the Guelph and Salina are well exposed in the Niagara gorge, the Cataract red or grey sandstone and shale resting upon the red Queenston shale at the mouth of the gorge. As one follows up the gorge the Cataract beds disappear beneath the rapids, and afterwards the Medina is lost, so that at the falls the lowest rock visible is the Clinton limestone.
The Niagara (Lockport) limestone is thin at Queenston Heights, at the mouth of the gorge, but grows thicker as one approaches the falls, owing to the gentle southward dip of the beds.
Dr. Parks mentions the following fossils as common in the Niagara and lower formations of the Silurian.