floods or droughts. Our knowledge of the meteorological condition of the
earth, at any period more than two centuries before our own time, is
derived from these imperfect details, from the vague statements of
ancient historians and geographers in regard to the volume of rivers and
the relative extent of forest and cultivated land, from the indications
furnished by the history of the agriculture and rural economy of past
generations, and from other almost purely casual sources of information.
[Footnote: The subject of climatic change, with and without reference to
human action as a cause, has been much discussed by Moreau de Jonnes,
Dureau de la Malle, Arago, Humboldt, Fuster, Gasparin, Becquerel,
Schleiden, and many other writers in Europe, and by Noah Webster, Forry,
Drake, and others in America. Fraas has endeavored to show, by the
history of vegetation in Greece, not merely that clearing and
cultivation have affected climate, but that change of climate has
essentially modified the character of vegetable life. See his Klima und
Pflansenwelt in der Zeit.]

Among these latter we must rank certain newly laid open fields of
investigation, from which facts bearing on the point now under
consideration have been gathered. I allude to the discovery of
artificial objects in geological formations older than any hitherto
recognized as exhibiting traces of the existence of man; to the ancient
lacustrine habitations of Switzerland and of the terremare of Italy,
[Footnote: See two learned articles by Pigorini, in the Nuova Antologia
for January and October, 1870.] containing the implements of the
occupants, remains of their food, and other relics of human life; to the
curious revelations of the Kjokkenmoddinger, or heaps of kitchen refuse,
in Denmark and elsewhere, and of the peat mosses in the same and other
northern countries; to the dwellings and other evidences of the industry
of man in remote ages sometimes laid bare by the movement of sand dunes