Although the measurable forces of radio-activity give on the whole a remarkably satisfactory time gauge and are doubtless more accurate than any method here discussed, it must not be considered that the ages given (p. 11) are absolute. The knowledge of geological time is of more importance for the comparative than for the absolute magnitude of the results obtained. Just as the study of astronomy gives us the conception of the vastness of space, so does the study of geology reveal to us that of the immensity of time. SHARAT K. ROY. [Illustration: LEAFLET 9. PLATE III. “IMMORTAL” TYPES. 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 ------------+-----------------+---------------+-------------------- | | TIME SCALE | ERAS | PERIODS |(After Barrell)| CHARACTERISTIC | +-------+-------+ LIFE | |Minimum|Maximum| ------------------------------+-------+-------+-------------------- PSYCHOZOIC | Recent | | | ------------+-----------------+ 1 | 1.5 | AGE OF MAN | Pleistocene | | | +-----------------+-------+-------+-------------------- | Pliocene | 7 | 9 | +-----------------+-------+-------+ CENOZOIC | Miocene | 19 | 23 | AGE OF MAMMALS +-----------------+-------+-------+ AND MODERN | Oligocene | 35 | 39 | FLOWERING PLANTS +-----------------+-------+-------+ | Eocene | 55 | 65 | ------------+-----------------+-------+-------+-------------------- | Cretaceous | 95 | 115 | +-----------------+-------+-------+ | Comanchian | 120 | 150 | MESOZOIC +-----------------+-------+-------+ AGE OF REPTILES | Jurassic | 155 | 195 | +-----------------+-------+-------+ | Triassic | 190 | 240 | ------------+-----------------+-------+-------+-------------------- | Permian | 215 | 280 | AGE OF AMPHIBIANS +-----------------+-------+-------+ AND | Pennsylvanian | 250 | 330 | ANCIENT FLORAS +-----------------+-------+-------+-------------------- | Mississippian | 300 | 370 | +-----------------+-------+-------+ AGE OF FISHES PALEOZOIC | Devonian | 350 | 420 |