Showing St. John group resting on Etcheminian, and this on Coldbrook
(Huronian).]
In Southern New Brunswick, Matthew indicated, several years ago, the
occurrence of certain conglomerates and sandy and slaty beds over the
rocks, mostly of igneous origin, constituting a great thickness of
beds under the Cambrian, and known locally as the "Coldbrook" series,
which is probably equivalent to the Huronian of Northern and Western
Canada, to be noticed later. These beds were at first regarded as an
upper member of the Huronian, but subsequently it was thought better
to unite them with the overlying Cambrian as basal Cambrian. The fact
that these problematical beds were ascertained to be unconformable to
the Cambrian, and the peculiarity of their fossils, led to their being
constituted a separate group under the name _Etcheminian_, which seems
to represent a time and conditions introductory to the Cambrian (Fig.
10). The fossils in these beds are few and hard to find. Matthew has
kindly furnished me with the following list.[7] The Trilobites are
conspicuous by their absence. Sea-worms have left burrows, trails, and
casts, which probably represent several species (Fig. 11). A single
little shell (Volborthella) is supposed to be a precursor of the
straight chambered shells allied to the modern nautilus, which become
so large and numerous in succeeding periods. There are a few univalve
shell-fishes allied to modern sea-snails, a brachiopod of the antique
genus Obolus, some fragments supposed to represent Cystideans, a
rudimentary type of the stalked sea-stars so abundant later, spicules
of sponges and minute Protozoa, with shells not unlike those of their
modern successors. This meagre list sums up the forms of life known
in the Etcheminian of this district, one in which the Cambrian beds
exhibit the rich and varied fauna of Trilobites and other animals
described and figured by Matthew in several successive volumes of the
"Transactions of the Royal Society of Canada" (Fig. 12).
[Footnote 7: "Transactions Royal Society of Canada," vol. vii.]
[Illustration: Fig. 11.--_Trails of Worms of two types (Psammchnites
and Planilites)._]
Beds in Newfoundland (the Signal Hill and Random Sound series),
underlying the Lower Cambrian, have afforded to Murray and Billings
some well-characterized worm-castings of spiral form, and a few
problematical forms known as Aspidella, which may be Crustaceans or
Mollusks allied to the limpets (Fig. 13).
[Illustration: Fig. 12.--_Group of pre-Cambrian (Etcheminian) Animals
from the Etcheminian._ (After Matthew.)]
The name "Etcheminian" is derived from that of an ancient Indian tribe
of New Brunswick.
(_a_) Volborthella, supposed to be a Cephalopod shell. (_b_)
Pelagiella. (_c_) Orthotheca, supposed to be Pteropods. (_d_) Primitia,
an Ostracod Crustacean, (_e_) Obolus, a Brachiopod shell. (_f_)
Platysolenites, probably fragment of a Cystidean. (_g_) Globigerinæ,
casts of Foraminiferal shells, Etcheminian, New Brunswick.
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