78 

 INTRODUCTION. 



The comparatively flat upland of the southwestern 

 part of the Province of Ontario is separated from the 

 eastern lowland by the Niagara cuesta which extends 

 from Queenston on the Niagara river to Hamilton at the 

 head of Lake Ontario and thence into the Bruce peninsula 

 between Lake Huron and Georgian bay. The brow 

 of the cuesta is marked by the Lockport (Niagara) dolomite 

 which extends only a short distance back from the edge 

 of the escarpment. 



The yellow dolomites of the Guelph formation succeed 

 the Niagara rocks and form a belt about 30 miles (48 km.) 

 wide with a length of 80 miles (129 km.). The actual 

 extent of the formation is probably much greater than 

 this, but the evidence is not very satisfactory owing 

 to the heavy covering of drift. Excellent exposures 

 from which the unique fauna of the formation may be 

 collected occur at Guelph, Gait, Hespeler, and at points 

 farther north. 



West of the Guelph formation, the unfossiliferous 

 shales and limestones of the Salina stretch in a broad 

 band from the Niagara river to Lake Huron. The western 

 boundary of this formation runs approximately from Fort 

 Erie to Goderich. Gypsum quarries are located on this 

 formation in the vicinity of Caledonia and Paris, while 

 at Goderich and Windsor it is the source of a large amount 

 of salt. 



The Salina is succeeded by the Monroe formation 

 which constitutes the summit of the Silurian series: it 

 is composed largely of dolomitic limestones and is separated 

 into an upper and lower member by a median bed of sand- 

 stone (Sylvania). Exposures of this formation are infre- 

 quent in Ontario: an unfossiliferous type is seen in the 

 "waterlime" of the Niagara district while a fossiliferous 

 dolomite with an interesting Silurio-Devonian fauna 

 is exposed by the Livingstone cut in the Detroit river 

 opposite Amherstburg. The Sylvania sandstone has 

 no areal extent in Ontario but it is always penetrated 

 in drilling the salt, gas and oil wells of the western part 

 of the province. 



The Oriskany sandstone, with a small but unique 

 fauna, marks the opening of Devonian time: the formation 



