October 8, 1915. 
Canada 
Geological Survey 
Museum Bulletin No. 20 
GEOLOGICAL SERIES, No. 29. 
An Eurypterid Horizon in the Niagara Formation of Ontario . 
By M. Y. Williams. 
GENERAL STRATIGRAPHY. 
The top of the Lockport member of the Niagara formation 
of Ontario consists of thin-bedded dark grey or chocolate brown 
bituminous dolomites which at some localities include bituminous 
shales. In some districts the cleavage along bedding planes 
is exceedingly even and slabs may be obtained that suggest 
roofing slates. Flagstones are quarried from such beds near 
Wiarton. At other localities the bedding is uneven, though 
thin. These characteristic beds are well exposed along the 
banks of the Eramosa river between Rockwood and Guelph, 
and for them the name “Eramosa beds” is proposed. Sir 
William Logan 1 described the Guelph dolomites in the vicinity 
of Guelph as resting “upon dark coloured bituminous strata” 
which he placed in the Niagara formation. His reference was 
to the beds under discussion. 
The Eramosa beds are very uniform in their general char- 
acters. At the north end of the Bruce peninsula they are 30 
feet thick; at Wiarton, they measure over 40 feet; at Guelph, 
30 feet or more; and at Spencer creek, 7 miles west of Hamilton, 
more than 35 feet. South of Hamilton, the highest of the 
dark slaty beds, known locally as the “Barton beds,” are 
probably the equivalent of the Eramosa. The Barton beds 
1 GeoL Siirv. of Can., Report of Progress, from its commencement to 1863, p. 337. 
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