442 
SILURIA. 
[Chap. XVIII. 
Looking, indeed, to the vast and little-accessible Arctic region, the geologist 
has good reason to be thankful for knowledge which has enabled him to classify 
the older sedimentary rocks of icy regions never trodden by civilized man before 
the present century. 
In terminating this brief outline of the succession of the older fossili- 
ferous rocks of America, let me remind the reader of the vast extent to 
which this continent is composed of Silurian, Devonian, and Carboniferous 
formations. In the "Western hemisphere, as in Europe, the first signs of 
life are met with at the same low horizon in the crust of the earth ; and 
similar great groups are clearly distinguishable. We also observe that 
Fishes, which, so far as clearly known, were called into existence only 
towards the close of the Silurian period *, and were of such peculiar forms 
in the Devonian epoch, become conspicuous in the Carboniferous depo- 
sits of America, and exhibit many new types, including the remarkable 
large Sauroid Pishes of Agassiz. Again, with a considerable amount 
of land vegetation in the Devonian, the Carboniferous rocks of America 
are characterized by the same abundant flora, and even by many spe- 
cies of the same shelly remains, as in Europe, together with sauroid 
animals. The only essential difference which, when the first edition 
of this work was published, was supposed to exist between the older rocks 
of the two hemispheres was, that America offered no indication of the 
upward termination of Palaeozoic life, which in Europe is marked by the 
Permian deposits. That distinction even has now been removed by the 
discovery of strata containing many true Permian species in the north- 
eastern part of Texas ; and the same formation is now known to occur also 
along the eastern edge of the Rocky Mountains f, — thus teaching us that 
Dublin Society, Feb. 1857, p. 26 ; and Keport Brit. 
Assoc. 1855, Trans. Sect. p. 211. 
* Eeasons were adduced, in tbe first edition, to 
prove that tbe forms supposed to belong to Fishes 
m the Niagara-limestone and Clinton Groups were 
probably parts of Crustaceans or of Annelides. 
The earliest Fishes yet known are from the 
Lower Ludlow rock. 
t The fossils which have brought out this co- 
incidence between the youngest Palaeozoic rocks 
of the New and Old World, were discovered by 
Major F. Hawn and Dr. Cooper, and being sent 
by them to Mr. Meek of New York, that gen- 
tleman and Dr. Hayden described some of 
them as belonging to Monotis, Myalina, Bake- 
vellia, Leda (Nucula), Pleurophorus, Panopsea, 
Nautilus, &c. See Trans. Albany Institute, 
March 1858. These authors had no doubt that 
the shells were of the Permian age. Professor 
Swallow of Missouri, to whom another collection 
had been sent by Major Hawn, arrived at the 
same conclusion, and enumerated several species 
identical with European forms, also many Corals. 
As these Permian fossils have already been pro- 
cured from spots 100 miles distant from each 
other, and have been even traced to the northern 
border of Missouri, the strata in each case over- 
lying the eroded surfaces of the Carboniferous 
rocks, I agree with the suggestion of Mr. Meek 
and Dr. Hayden, that the formation will be found 
to have a considerable geographical range in the 
far West. 
M. Jules Marcou (who passed some months in the 
elevated region of the Eocky Mountains of Mexico) 
has discovered an Upper Carboniferous zone co- 
vered by a magnesian limestone, and followed by 
Triassic, Jurassic, Cretaceous, and Tertiary rocks. 
This view of the order of succession was commu- 
nicated inl853 to theGeological Society of France ; 
and, recurring to it in other works, and in his 
general map, published in succeeding years, M. 
Marcou afterwards brought together all his 
observations in one volume. (' Geology of North 
America ; with two Eeports on the Provinces of 
Arkansas and Texas, the Eocky Mountains of New 
Mexico, and the Sierra Nevada of California, 
originally made for the United States Govern- 
ment.' April 1858, Zurich. See also Bibl. Univ. 
de Geneve, Juin 1858.) That the magnesian lime- 
stone above the Coal, of which that author has 
spoken, is truly of Permian age, has recently been 
thoroughly ascertained through Professor Gei- 
nitz's examination of its fossils brought from 
the cliffs of Nebraska City by M. Marcou. In one 
central band of these rocks, 63 fossils were found. 
Of these, 22 species prove to be known in the Per- 
mian rocks of" Europe, 21 are new species, and 20 
are common to the Permian and Carboniferous 
deposits. (See Marcou, Bull. Soc. Ge'ol. de France, 
vol.xxi. p. 132, and Geinitz, Jahrbuch,1867,pp.l-9.) 
This collocation of fossils proves indisputably that 
the Permian formation in America is, as in Eu- 
rope, truly Palaeozoic ; being linked on to the Car- 
boniferous system just as Devonian rocks pass up- 
wards into the Carboniferous and downwards into 
the Silurian system. We are thus well assured 
that the numerical term Dyas, which Geinitz and 
Marcou would substitute for the generally re- 
