Are there certain animals and plants peculiar to certain strata, and not found in others? What are the species that appear first in order, and what those which succeed? Do these two kinds of species sometimes accompany each other? Are there alternations in their appearance; or, in other words, do the first reappear a second time, and do the others then disappear? Have these animals and plants all lived in the places where their remains are found, or have they been transported thither from other places? Do they all live at the present day in some part of the earth, or have they been partially or totally destroyed? Is there any constant connection between the antiquity of the strata and the resemblance, or non-resemblance, of the fossils contained in them to the animals and plants which now exist? Is there any connexion, in regard to climate, between the fossils and such living beings as resemble them most? May it be concluded, that the transportation of these living beings, if such a thing ever happened, has taken place from north to south, or from east to west; or were they irregularly scattered and mingled together; and can the epochs of these transportations be determined by the characters which they have impressed upon the strata? What can be said regarding the causes of the existing state of the globe, if no reply can be made to these questions,--if there be no sufficient grounds to determine the choice between answering in the affirmative or negative? It is but too true, that, for a long time, none of these points was satisfactorily determined; and scarcely even would geologists seem to have had any idea of the propriety of clearing them up before constructing their systems. _Reason for which the Conditions of the Problem have been neglected._ The reason of this strange procedure will be discovered, when we reflect, that all geologists have hitherto been, either mere cabinet naturalists, who had themselves paid little attention to the structure of mountains, or mere mineralogists, who had not studied in sufficient detail the innumerable varieties of animals, and the infinite complication of their various parts. The former of these have only constructed systems: the latter have furnished excellent observations, and have laid the foundation of true geological science; but have been unable to complete the edifice. _Progress of Mineral Geology._ The purely mineral part of the great problem of the Theory of the Earth has been investigated with admirable care by Saussure, and has been since carried to an astonishing degree of development by Werner, and by the numerous enlightened pupils of his school.