NATURAL HISTORY, TORONTO REGION 
Srvgkiayn. 
The Silurian (Upper Silurian) of southwestern 
Ontario includes a number of fairly distinct subdivi- 
sions 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, ete. 
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 com- 
mon in the Niagara and lower formations of the 
Silurian. 
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