546                                                 SILUEIA.

represented in a general way. Everywhere we find a number of breaks or gaps,
and the probabilities are vastly against these having been aU occasioned at the
same time in distant localities."

I rejoice to see this sentiment confirmed by eminent palaeontologists of distant
countries. As to the numerous breaks which were ably pointed out by Professor
Ramsay in the Silurian series of England, Mr. BiUings also treats of these in
North America. Now it is weU known to every practical geologist that such
breaks run through every great series or system of rocks, whether Palaeozoic,
Secondary, or Tertiary; and therefore it is evident that perfect paraUelism of the
minor groups of distant countries can only be looked for as exceptions, and not
as the rule.

It further appears from the writings of Mr. BiUings, that the base of the
* Primordial' Silurian Zone of Barrande, seen in the slates and schists near
Boston and in Minnesota and Wisconsin, has not been found in Canada, and that
what has there been caUed' Potsdam Sandstone' is of somewhat more recent age
(see the Table, p. 446-7).

N.—Palceozoic RocJcs of Illinois in the United States (p. 427 et seq.).

The work entitled ' The Geological Survey of lUinois,' as carried out under the
direction of Mr. A. H. Worthen, assisted by Professors "WTiitney and Lesquereux
and Mr. H. Engelman, which reached me after the Chapter on America was
completed, gives a well condensed and clear account of the whole series of rocks
in that highly prosperous young State.

The Lower Silurian of these authors consists of Lower Magnesian Limestone,
covered by the St. Peter's Sandstone, the Galena and Trenton Limestones, and
the Cincinnati group of strata overlying them.

The Upper Silurian consists of the Niagara (or Wenlock) Limestone, and a
superior deposit called Clear-Creek Limestone. The Devonian rocks are made
up of Oriskany Sandstone, the ' Devonian Limestone,' and ' Black Slate.'

The Lower Carboniferous (^Infra-carboniferous') exhibits five stages, including
one of Umestone. It is surmounted by conglomerate (JMillstone-grit) and Coal-
measures.

In the second volume the organic remains, chiefly those of the Carboniferous
system, are elaborately described, with many plates.

0.—Minute Silurian Fossils in Anyerica (p. 446).

Among the fossils of the Silurian rocks might be mentioned the microscopic
organisms discovered by Dr. M. C. ^Tiite in nodules of hornstone, occurring
plentifuUy in the Black-river Limestone (as weU as in some Devonian hme¬
stones) of North America. These Uttle fossUs are apparently Desmids and
Diatoms, Sponge-spicules, and fr-agments of the teeth of Gasteropods j and, in
the case ofthe microphytes above-mentioned, " they carry back to a very early
epoch forms of life which have hitherto been looked upon as belonging only to
a much more recent era in the life of our planet."—American Joum. Sc. Arts,
May 1862, and Geologist, vol. v. p. 239.

P.—Produce and Relations of the Gold-mines near Dolgelly, Merioneth¬
shire (p. 450).

The mine of Clogau is the property of the Crown j and owing to the obUging