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 all 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. Billings also treats of these in 
North America. Now it is well 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 parallelism 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. Billings, 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 called ' Potsdam Sandstone ' is of somewhat more recent age 
(see the Table, p. 446-7). 
N. — Palaeozoic Bocks of Illinois in the United States (p. 427 et seq.). 
The work entitled 6 The Geological Survey of Illinois/ as carried out under the 
direction of Mr. A. H. Worthen, assisted by Professors Whitney 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 limestone. It is surmounted by conglomerate (Millstone-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 America (p. 446). 
Among the fossils of the Silurian rocks might be mentioned the microscopic 
organisms discovered by Dr. M. C. White in nodules of hornstone, occurring 
plentifully in the Black-river Limestone (as well as in some Devonian lime- 
stones) of North America. These little fossils are apparently Desmids and 
Diatoms, Sponge-spicules, and fragments of the teeth of Gasteropods ; and, in 
the case of the 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 Journ. 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 ; and owing to the obliging 
