There is no reasonable debate as to the passage of one species to another. It is clearly manifested in the succession of fauna found today all over the world in the sedimentary rocks. Even the most casual student of paleontology is convinced of this glaring truth. “The brutal cogency of a slab of fossils could be hated and fought, but could not be gainsaid.” But when we are confronted with the question of setting a standard of measuring geologic time by means of this paleontological record, more precisely, through this biological process, we cannot help pondering over the grave uncertainty of the result. When we fix our gaze upon a trilobite, a three-lobed, crab-like creature (Pl. II fig. 1) that ruled the seas in the dim days of the Cambrian period (p. 11) and see that it was equipped with gills and swimming organs, with powers of digestion and excretion, with specific organs of circulation and reproduction and with motor and sensory nerves, and compare it with one of its tribe, a present day horseshoe crab, (Pl. II fig. 2) we do not find any noticeable progress in structure, in intricacy or in the degree of specialization. Yet the time that has elapsed since the Cambrian is, according to a moderate estimate, nearly 600,000,000 years! (p. 11). Geologic record testifies that evolution awaits environmental change, that animals in some way adjust themselves to their environment, either by discarding or modifying old characters or by acquiring new ones. Yet, what are known as “immortal” types, such as the brachiopods, Lingula, Crania and Terebratula (Pl. III figs. 1-3) or the pelecypods, such as Pecten, Pinna and Arca (Pl. III figs. 4-6) or the gastropods, such as Pleurotomaria, Natica and Trochus (Pl. III figs. 7-9), have withstood all possible environmental changes and have steadfastly held their own ever since we have records of their very early appearance on earth. On the contrary, we have records of types that have yielded so rapidly to change that their evolution is almost explosive. It is almost incomprehensible how, within such a limited period of time, fishes have changed into amphibians, amphibians into reptiles, and reptiles into birds and mammals (Pl. IV figs. 1-4). With these conflicting evidences staring us in the face, with the knowledge that the entire organic world has been subject to earth-wide periods of long stagnation and rapid intensive change, one may well ponder whether it is within our power to establish a standard for measuring geologic time on the evidence of life transformation. The study of the succession of faunas—the change of one species to another, can only indicate the magnitude of time involved. It cannot afford any basis, whatsoever, for a concrete expression of geologic time.