It contains a number of peculiar
Graptolites, by which it can be identified without question with
the Arenig group of Wales and the corresponding Skiddaw Slates
of the North of England. It is also to be noted that numerous
Trilobites of a distinct Cambrian _facies_ have been obtained in
the limestones of the Quebec group, near Quebec. These fossils,
however, have been exclusively obtained from the limestones of
the group; and as these limestones are principally calcareous
breccias or conglomerates, there is room for believing that these
primordial fossils are really derived, in part at any rate, from
fragments of an upper Cambrian limestone. In the State of New
York, the Graptolitic shales of Quebec are wanting; and the base
of the Silurian is constituted by the so-called "Calciferous
Sand-rock" and "Chazy Limestone."[11] The first of these is
essentially and typically calcareous, and the second is a genuine
limestone.
[Footnote 11: The precise relations of the Quebec shales with
Graptolites (Levis Formation) to the Calciferous and Chazy beds
are still obscure, though there seems little doubt but that the
Quebec Shales are superior to the Calciferous Sand-rock.]
2. The _Trenton Group_.--This is an essentially calcareous group,
the various limestones of which it is composed being known as
the "Bird's-eye," "Black River," and "Trenton" Limestones, of
which the last is the thickest and most important.
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