142 
tenutfilum, Bumastus muillert, Dalmanella_ gibbosa, and 
Strophomena filitexta. 
The Black River at and north of Montreal agrees with 
the Leray formation of New York in having an abundance 
of flat, disk-shaped masses of black chert; but west of 
Montreal and in the vicinity of Ottawa the chert seems to 
be absent. The formation is from 30 to 40 feet (g-I to 
12-2" mM.) whack. 
TRENTON GROUP. 
The Trenton at Montreal is very different from the 
Trenton at Ottawa, and the exposures in the region between 
the two cities are so poor that the correlation had to be 
made through the Champlain and Mohawk valleys, around 
the Adirondacks into central Ontario, and thence to the 
Ottawa section. Asa result of this correlation, it appears 
that the oldest beds in the Trenton at Ottawa are younger 
than the lower 100 feet (30-4 m.) of the Trenton at Mont- 
real; that is, that the Dalmanella beds at Ottawa are young- 
er than the 7rinucleus beds at Montreal (see table above) 
and that the “‘Trentons”’ of the two cities correspond 
only in a general way. At Montreal, the lower part of 
the Trenton is well shown, but the upper part is exposed 
badly or not at all. All the strata there are rather thin- 
bedded, blue-black limestones, and the lowest beds contain 
the fauna with Parastrophia hemtiplicata. A thickness of 
about 40 feet (12-2 m.) of these strata is overlain by some 
50 feet (15-2 m.) of limestone with Trinucleus concentricus, 
Triplecia nuclea, Trematis terminalis, and other fossils. 
This same zone can be traced as far west as Trenton Falls 
in New York, where it is at the very base of the typical 
section, but it is unknown farther west. At Trenton Falls 
and elsewhere in New York, this zone is succeeded by the 
fauna with Tyriplecia extans and Triplecia cuspidata, 
Orthis tricenaria, etc., which is the Dalmanella fauna at the 
base of the Ottawa section. Whether or not this fauna is 
present at Montreal has not yet been determined, but the 
next zone, with the Prasopora fauna, is probably continuous 
over the whole area. At Montreal the exposed section 
stops with the lower part of the Prasopora beds. | 
At Ottawa, the following zones have been recognized, 
beginning with the lowest :— 
Dalmanella Beds.—Thin-bedded, pure, blue-black 
limestone, characterized by Orthts tricenaria, etc. These 
