. The origin and evolution of life, on the theory of action, reaction and interaction of energy. s of limestone and in the deposits of iron and graphite^which, as we have already observed, are considered proofs ofthe existence at enormously remote periods of limestone-forming algae, of iron-forming bacteria, and of a variety ofchlorophyll-bearing plants. These evidences begin with themetamorphosed sedimentaries overlying the basal rocks of thecrust of the primal earth. Pre-Cambrian and Cambrian Forms of Invertebrates The discovery by Walcotf- of a world of highly specializedand diversified inv
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. s of limestone and in the deposits of iron and graphite^which, as we have already observed, are considered proofs ofthe existence at enormously remote periods of limestone-forming algae, of iron-forming bacteria, and of a variety ofchlorophyll-bearing plants. These evidences begin with themetamorphosed sedimentaries overlying the basal rocks of thecrust of the primal earth. Pre-Cambrian and Cambrian Forms of Invertebrates The discovery by Walcotf- of a world of highly specializedand diversified invertebrate life in the Middle Cambrian seascompletely confirms the prophecy made by Charles Darwin in 1 Joseph Barrell. See Pirsson, Louis V., and Schuchert, Charles, 1915, p. Walcott, Charles D., 1911, 1912. CAMBRIAN INVERTEBRATES 119 1859^ as to the great duration that must be assigned to pre-Cambrian time to allow for the evolution of highly specializedlife forms. By Middle Cambrian time the adaptive radiation of theInvertebrata to all the conditions of life—^in continental waters,. PALEOGEOGRAPHY. LATE LOWER CAMBRIAN (WAUCOBIAN OR OLENELLUS) TIMEAFTER SCHUCHERT, APRIL, 1916^^MARINE DEPOSITS «» ACTIVE VOLCANOES IM SCOTLAND *- MOUNTAINS A ■ ARCMAEOCYATHINAE Fig. 19. Theoretic World Environment in Late Lower Cambrian Time. This period corresponds with that of the first well-known marine fauna with trilobitesand brachiopods as the dominant forms. No land life of any kind is known, and theclimate appears to have been warm and equable the world over. After Schuchert. along the shore-lines, and in the littoral and pelagic environ-ment of the seas—appears to have been governed by mechan-ical and chemical principles fundamentally similar to thoseobserved among the Protozoa, but distributed through myriadsof cells and highly complicated tissues and organs, instead ofbeing differentiated within a single cell as in the ciliate Pro-tozoa. Among the elaborate functions thus
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