1, LINGULA. 2, CRANIA. 3, TEREBRATULA. 4, PECTEN. 5, PINNA.
6, ARCA. 7, PLEUROTOMARIA. 8, NATICA. 9, TROCHUS.
(Figs. 1, 2, 7, after Hall, 3, 9, after Zittel, 4, 6, after Dall,
5, Pal. N. J. I, 8, after Cragin).
Drawings by Carl F. Gronemann.
THE GEOLOGICAL TIME TABLE
1.0 = One million years
| ERAS | PERIODS | TIME SCALE (After Barrell) | CHARACTERISTIC LIFE | |
|---|---|---|---|---|
| Minimum | Maximum | |||
| PSYCHOZOIC | Recent | 1 | 1.5 | Age of Man |
| CENOZOIC | Pleistocene | |||
| Pliocene | 7 | 9 | Age of Mammals and Modern Flowering Plants | |
| Miocene | 19 | 23 | ||
| Oligocene | 35 | 39 | ||
| Eocene | 55 | 65 | ||
| MESOZOIC | Cretaceous | 95 | 115 | Age of Reptiles |
| Comanchian | 120 | 150 | ||
| Jurassic | 155 | 195 | ||
| Triassic | 190 | 240 | ||
| PALEOZOIC | Permian | 215 | 280 | Age of Amphibians and Ancient Floras |
| Pennsylvanian | 250 | 330 | ||
| Mississippian | 300 | 370 | Age of Fishes | |
| Devonian | 350 | 420 | ||
| Silurian | 390 | 460 | Age of Higher Shelled Invertebrates | |
| Ordovician | 480 | 590 | ||
| Cambrian | 550 | 700 | ||
| PROTEROZOIC | Systematic classification variable | 925 | Age of Primitive Invertebrates | |
| Long Erosional Interval | ||||
| ARCHEOZOIC | 1500 | Dawn of Unicellular Life, Algal Forms Reported | ||
BIBLIOGRAPHY
Barrell, J.—Rhythms and Measurements of Geological Time.
Bull. Geol. Soc. Am., Vol. 28, 1917, pp. 745-904.
Becker, Geo. E.—The Age of the Earth.
Smithsonian Misc. Coll., LVI., No. 6, 1910.
Chamberlain, T. C.—Diastrophism and the Formative Processes, XIII.
The Time over which the Ingathering of the Planetesimals was Spread.
Jour. Geol., Vol. XXVIII, 1920, pp. 675-81.