Page:The Journal of geology (IA journalofgeology11893univ).pdf/210
One of the fullest elaborations of this biological classification of the geological series to form a time-scale is found in Dana's Manual of Geology. (Manuel of Geology; treating of the principles of the science with special reference to American Geological History, by James D. Dana, 3d ed., New York, 1880.) Here we find the larger divisions called times: I, Archean; II, Palæozoic; III, Mesozoic and IV, Cenozoic times. The Palæozoic time is classified into ages, viz: The age of Invertebrates, the Cambrian and Silurian; the age of Fishes, the Devonian; the age of Coal Plants, the Carboniferous. The Mezozoic is called the age of Reptiles. The Cenozoic time includes the age of mammals and the age of man.
Each of the ages is subdivided into periods and epochs, in which the stratigraphical groups and formations form the basis, and the particular faunas and floras of each constitute the data of determination for the time divisions. Thus the Devonian age includes the following:
| Periods. | ||
|---|---|---|
| Catskill | =Devonian Age; | |
| Chemung | ||
| Hamilton | ||
| Corniferous | ||
and, as an example, the Corniferous Period includes the following epochs:
| Corniferous | =Corniferous Period. | |
| Schoharie | ||
| Cauda-galli |
The distinctions upon which these subdivisions are made are primarily stratigraphical, and we have still to seek a time-classification on a purely biological basis for the whole geological series.
One of the earliest attempts at systematic classification upon a purely biological basis, was made by Dr. Oppel in classifying the Jurassic formations on the basis of the successive Ammonites characterizing the beds. (A. Oppel, Die Juraformation, Eng-