Page:The Journal of geology (IA journalofgeology11893univers).pdf/248
giving the standard time-unit used the name geochrone. The geochrone used by him in obtaining a standard scale of geochronology is the period represented by the Eocene. His time-scale gives 15 for the Paleozoic; 3 for the Mesozoic; and 1 for the Cenozoic, including the Quaternary and the Recent.[1]
The Rev. Samuel Haughton obtained the following time-ratios from the maximum thickness of strata as they occur in Europe:
| Period. | From Theory of Cooling Globe. | From Maximum Thickness of Strata. | ||
|---|---|---|---|---|
| Azoic | 33.0 | per cent. | 34.3 | per cent. |
| Paleozoic | 41.0 | " | 42.5 | " |
| Neozoic | 26.0 | " | 23.2 | " |
| Total | 100.0 | per cent. | 100.0 | per cent. |
He draws from this the principle—"The proper relative measure of geological periods is the maximum thickness of the strata formed during these periods."[2]
In considering the time-ratios for the Paleozoic, Mesozoic, and Cenozoic rocks of the North American continent, as given by Dana and Williams, I think that a too small proportion has been given to the Mesozoic and Cenozoic. In the Mesozoic of the western-central area occur the coal deposits of the Laramie series and the great development of limestone (from 10,000 to 20,000 feet) in the Cretaceous of Mexico. The limits of this paper do not permit of a discussion of the available data bearing upon geologic time-ratios; but from a comparison of the Paleozoic, Mesozoic, and Cenozoic strata and the geologic phenomena accompanying their deposition, I would increase the comparative length of the Mesozoic and Cenozoic periods so that the time-ratios would be: Paleozoic, 12; Mesozoic, 5; Cenozoic, including Pleistocene, 2.
DURATION OF POST-ARCHEAN GEOLOGIC TIME.
Taking as a basis 17,500,000 years for Paleozoic time and the time-ratios, 12, 5, and 2 for Paleozoic, Mesozoic, and Ceno-