Although in some respects more technical in their subjects and style thanDarwin’s “Journal,” the books here reprinted will never losetheir value and interest for the originality of the observations they contain.Many parts of them are admirably adapted for giving an insight into problemsregarding the structure and changes of the earth’s surface, and in factthey form a charming introduction to physical geology and physiography in theirapplication to special domains. The books themselves cannot be obtained formany times the price of the present volume, and both the general reader, whodesires to know more of Darwin’s work, and the student of geology, whonaturally wishes to know how a master mind reasoned on most importantgeological subjects, will be glad of the opportunity of possessing them in aconvenient and cheap form.
The three introductions, which my friend Professor Judd has kindly furnished,give critical and historical information which makes this edition of specialvalue.
Rocks of the lowest series.—A calcareous sedimentary deposit, with recentshells, altered by the contact of superincumbent lava, its horizontality andextent.—Subsequent volcanic eruptions, associated with calcareous matterin an earthy and fibrous form, and often enclosed within the separate cells ofthe scoriae.—Ancient and obliterated orifices of eruption of smallsize.—Difficulty of tracing over a bare plain recent streams oflava.—Inland hills of more ancient volcanic rock.—Decomposedolivine in large masses.—Feldspathic rocks beneath the upper crystallinebasaltic strata.—Uniform structure and form of the more ancient volcanichills.—Form of the valleys near the coast.—Conglomerate now formingon the sea beach.
FERNANDO NORONHA.—Precipitous hill of phonolite.
TERCEIRA.—Trachytic rocks: their singular decomposition by steam of hightemperature.
TAHITI.—Passage from wacke into trap; singular volcanic rock with thevesicles half-filled with mesotype.
MAURITIUS.—Proofs of its recent elevation.—Structure of its moreancient mountains; similarity with St. Jago.
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