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beds are very poorly exposed at Ottawa, and have an esti- 
mated thickness of about 40 feet (I12.2m.). They are well 
shown above the Black River in the Stewart quarry at 
Rockland, and were also seen on top of the Black River at 
Fenelon Falls and Kirkfield lift-lock in central Ontario. 
Crinoid Beds—Thick and thin-bedded blue lime- 
stone, with a large amount of chert, developed as flat plates 
parallel to the bedding. These beds are particularly well 
shown in Hull, and furnish a large part of the building stone 
and crushed stone used in Ottawa. Just at the top of 
these beds are the layers from which a large part of the 
crinoids found in Hull have been obtained. Strata with 
the same fauna as these beds occur in central Ontario at 
Fenelon Falls and the Kirkfield lift-lock, where they occupy 
the same stratigraphic position as at Ottawa. The thick- 
ness of these beds is about 65 feet (19.8 m.). 
Tetradium Beds.—Massive, coarse-grained,  blue- 
gray limestone with few fossils. This is the horizon in 
which are located the large quarries on Montreal road, 3 
miles (4.8 km.) east of Ottawa. The same beds are ex- 
posed in Hull, but are not quarried at the present time. 
They seem to be absent from the section in central Ontario. 
The most common fossil is a species of Tetradium, very like 
Tetradium cellulosum. The thickness is about 35 feet 
(10.6 m.). 
Prasopora Beds.—Very thin-bedded limestone, with 
thick shale partings, characterized by abundant large 
bryozoans of the genus Prasopora. This bed seems to 
have a very wide distribution, and the fossils are well pre- 
served. In spite of their thin-bedded and shaly character, 
the strata of this zone are extensively quarried. The 
thickness of the zone is small, usually not more than 25 feet 
(7.6 m) and frequently less. 
Cystid Beds.—Rather thin-bedded light gray lime- 
stone with thin shale partings. In the lower portion is 
the zone with Pleurocystites and Agelacrinites. Thickness, 
about 75 feet (22.8 m.). 
Sponge Beds.—Heavy-bedded, fine-grained limestone 
with clay irregularly distributed through it. These layers 
weather into an irregular rubbly mass, and are character- 
ized by Hormotoma trentonensis, Rafinesquina deltoidea, 
and Cyclospira bisulcata. The thickness is about 75 
feet (22.8 m.). 
