must be sought much farther back
than any records which have yet been discovered. The researches of
palaeontologists and embryologists indicate a reptilian origin for birds
and mammals, while reptiles and amphibia arose, perhaps independently,
from fishes.

_Concluding Remarks._

The brief review we have now taken of the more suggestive facts
presented by the geological succession of organic forms, is sufficient
to show that most, if not all, of the supposed difficulties which it
presents in the way of evolution, are due either to imperfections in the
geological record itself, or to our still very incomplete knowledge of
what is really recorded in the earth's crust. We learn, however, that
just as discovery progresses, gaps are filled up and difficulties
disappear; while, in the case of many individual groups, we have already
obtained all the evidence of progressive development that can reasonably
be expected. We conclude, therefore, that the geological difficulty has
now disappeared; and that this noble science, when properly understood,
affords clear and weighty evidence of evolution.

FOOTNOTES:

[Footnote 183: The reader who desires to understand this subject more
fully, should study chap. x. of the _Origin of Species_, and chap. xiv.
of Sir Charles Lyell's _Principles of Geology_.]

[Footnote 184: On "Stagonolepis Robertsoni and on the Evolution of the
Crocodilia," in _Q.J. of Geological Society_, 1875; and abstract in
_Nature_, vol. xii. p. 38.]

[Footnote 185: From a paper by Messrs. Scott and Osborne, "On the Origin
and Development of the Rhinoceros Group," read before the British
Association in 1883.]

[Footnote 186: American Addresses, pp. 73-76.]

[Footnote 187: Lecture on the Introduction and Succession of Vertebrate
Life in America, _Nature_, vol. xvi. p. 471.]

[Footnote 188: _Nature_, vol. xxv. p. 84.]

[Footnote 189: See _The Mammalia in their Relation to Primeval Times_,
p. 102.]

[Footnote 190: For a brief enumeration and description of these fossils,
see the author's _Geographical Distribution of Animals_, vol. i. p.
146.]

[Footnote 191: Sketch of Palaeobotany in Fifth Annual Report of U.S.
Geological Survey, 1883-84, pp. 363-452, with diagrams. Sir J. William
Dawson, speaking of the value of leaves for the determination of fossil
plants, says: "In my own experience I have often found determinations of
the leaves of trees confirmed by the discovery of their fruits or of the
structu