d the kinds and
distinguishing characteristics of those that make up the earth's
surface; the second presenting the arrangement of rocks, stratified and
unstratified,--the structure due to deposition and other agencies,--the
dislocations of strata, and the consequent faults and distortions of
fossils contained in them,--together with considerations upon the age
and chronological division of all the strata of the earth's surface.

_Historical Geology_.--This third part of the volume, and that which
peculiarly characterizes the work, opens with some general remarks upon
the divisions in Geological History, and the announcement of certain
important principles to be kept in view while considering the subject.
The progress of life is then described as the basis of subdivision into
Geological Ages; and the subdivisions of geological time are presented
as follows:--

I. Azoic Time or Age.

II. Palaeozoic Time.
1. The Age of Mollusks, or Silurian.
2. The Age of Fishes, or Devonian.
3. The Age of Coal Plants, or Carboniferous.

III. Mesozoic Time.
4. The Age of Reptiles.

IV. Cenozoic Time.
5. The Age of Mammals.

V. Era of Mind.
6. The Age of Man.

And in connection with this is given a table of the further subdivision
of this history into Geological Periods, and a map showing the
distribution of the rocks of each of these periods over the surface of
the United States.

The great divisions above given are, as stated, essentially the same as
proposed by Professor Agassiz, who, however, made the era of Fishes to
embrace the first and second ages of Palaeozoic Time, the Silurian and
the Devonian, instead of restricting it, as now done, to the latter, and
calling the former the Age of Mollusks.

Following these general considerations, each great division of geologic
time is successively taken up, commencing with the Azoic. Each period
of the several divisions is treated of in order; and the rocks of
each epoch and their distribution described, first, as they exhibit
themselves in America,--then, more briefly, as they appear in Europe.
A full account of the life that manifested itself in each epoch, both
vegetable and animal, is likewise given in the same order. The igneous
and other disturbing agencies are then considered, and general remarks
added upon the geography, the character of the surface, and various
phenomena of the period.

The whole of this portion of the work is abunda