Chap. XVIII.] ASCENDING ORDEE IN NORTH AMERICA. 
427 
the adjacent territories, have recognized Silurian rocks, both Lower and Upper, 
followed by deposits of Devonian and Carboniferous age *. In the Canadas, 
where Bigsby and others were his precursors, Logan, the Director of the Geo- 
logical Survey of that great Colony, has mapped enormous tracts both of Lower 
and Upper Silurian rocks j whilst Richardson, triumphing over all the obstacles 
of the inclement North, has followed Silurian limestones along the western 
flank of the gneissic chain from Lake Winnipeg to the mouth of the Mackenzie 
River. The latter has also shown to how great an extent these strata wrap 
round the huge crystalline nucleus of North America, and form the edges of the 
continent towards the Arctic Sea. In many of the Arctic islands, too, Upper- 
Silurian fossils have been detected by the skilful navigators who have sailed in 
search of the lamented Franklin. 
Let me first allude to some of those tracts which, through the labours of geo- 
logists in the United States, have been rendered classical in our science, and 
where the types of comparison have been sedulously and accurately de- 
scribed f. 
Palceozoic Mocks of the United States. — The State of New York presents a 
noble series of Palaeozoic deposits, as laid open on the banks of many rivers. 
By the examination of these natural sections, the geologists of that great State 
have been enabled to describe a detailed order which is remarkable for its sym- 
metry and unbroken condition from the base of the Lower Silurian to the Coal- 
measures inclusive, the whole being generally arranged in slightly inclined 
and conformable strata % : — 
1. Silurian Rocks. — The local subdivisions (about eighteen in number, and of 
very unequal dimensions) of which the Silurian system, so admirably described 
by Mr. James Hall, is composed in the State of New York are compared with 
their European equivalents in a Table which follows (p. 446). Independent, 
however, of these numerous subdivisions, the lower portion of the series has 
been admitted by American authorities to be divisible, as in Europe, into two 
groups, each characterized by peculiar fossils. Thus, from the ' Potsdam Sand- 
stone,' or base of the whole fossiliferous series, up to the slates and arenaceous 
schists of the Hudson-river Group, overlying the Trenton Limestone, the mass 
so composed represents the Lower Silurian. In this view, de Verneuil, Logan, 
of the United States and British North America : 
Boston, 1853. This work contains a list of writers 
on American Geology. Lastly, the numerous 
books and memoirs descriptive of the geological 
researches both of the State- Geologists and of the 
Explorers of the great western territories and the 
passes of the Eocky Mountains ; as well as the 
reports of the Arctic voyagers. 
* It was my anxious desire to visit the United 
States and the Canadas in 1858, when illness 
prevented the enjoyment and instruction I had 
promised myself. As, however, my place was 
taken by my associate Eamsay, whose acquaint- 
ance with the British Palaeozoic rocks is as exten- 
sive as it is accurate, I was fortunately enabled, 
through his communications, not only to correct 
several errata in the first edition, but to bring the 
older formations of America into a much more 
accurate parallel with our own deposits than 
could otherwise have been attempted. This will 
be specially shown by a comparison of the Silu- 
rian and Devonian rocks of America and Britain, 
in a Table at page 446. 
t My cotemporaries in America, whose labours 
I highly estimate, will readily understand that in 
a work which is limited to the general history of 
Palaeozoic rocks, and specially those of Europe, I 
have no space to render justice to the numerous 
able writings which treat of those tracts of the 
United States or the British Colonies where such 
rocks are little developed. Thus the works of 
Hitchcock, whose description of the structure of 
his native State, Massachusetts, with its accom- 
panying map, are models of geological mono- 
fraphy, — of Dana, whose insight into the natural 
istory of Zoophytes, and whose philosophic re- 
flections on the outlines of the earth, have secured 
for him a wide reputation, — and the various con- 
tributions to the excellent 'Journal' of my friend 
the late Professor Silliman, — must now be passed 
over, although, if general geology were my ob- 
j ect, they would be eagerly appealed to. Nor will 
the reader find in the text any allusion to the 
labours of some authors who nave been highly 
useful in building up the now well-established 
series of the older formations, such as Maclure, 
Eaton, Troost, Emmons, Perceval, Vanuxem, 
Conrad, Jackson, Foster, Thompson, Whitney, 
and others. The few works above referred to are 
necessarily those in which the authors have di- 
lated on the subjects which are specially treated 
of in this volume — namely, comparative views of 
Palaeozoic Geology. 
I The Synoptical View of the Mineralogical 
and Fossil Characters of the Palaeozoic Strata of 
the State of New York, by Dr.Bigsby, in the Quart. 
Journ. Geol. Soc. vol. xiv. pp. 335 & 427, and vol. 
xv. p. 251, is about to be followed by an inestimable 
work, the ' Thesaurus Siluricus.' 
