EVOLUTION OF LIMESTONE AND DOLOMITE 343 



the character of deposits now forming in shallow or moderate 

 depths. None are like the abysmal deposits of the present ocean, 

 a forceful argument for the permanence of the continents and the 

 oceans. Nor is there any probability that the temperature of the 

 ocean has undergone a progressive change which would account 

 for the evolution of limestones and dolomites. The continuity of 

 the. life record down to the base of the Cambrian precludes the 

 possibility of any marked change in the temperature of the ocean 

 throughout Zoic times. But even beyond the Cambrian this 

 relative uniformity of temperature may have persisted for a period 

 of time, as long or even longer than from the Cambrian to the 

 present, for paleontologists believe that approximately nine-tenths 

 of the evolution of life into main stocks was completed at the begin- 

 ning of the Cambrian. All the phyla are represented in the Cam- 

 brian excepting the vertebrates, and the fact that no vertebrate 

 fossils have been found in the Cambrian cannot be regarded as 

 positive proof that even they did not exist at this remote period 

 of earth history. On the other hand, more and more evidence 

 is accumulating in favor of Chamberlin's philosophic conception 

 that the temperature of the ocean and the climatic conditions of 

 the continents have undergone oscillations in consequence of 

 periodic, areal changes of the lands with respect to the sea; that 

 periods of land expansion are characterized by zonal, diversified 

 climates, tending toward world-wide aridity and refrigeration, 

 while periods of maximum oceanic expansion are associated with 

 climatic uniformity, moderation, and humidity. There is then no 

 probability that the temperatures of the ocean have undergone an 

 evolution consonant with the evolution of dolomite and limestone. 



Could the evolution of living organisms have been the control- 

 ling factor in the evolution of limestones and dolomites ? 



It would be difficult to disprove that organic control was a 

 factor in the problem. Organisms play a gigantic role in the dis- 

 tribution of lime at the present time, and have for ages past. 

 Biologists, however, lend considerable support to the hypothesis 

 that organic activities are adaptations to physical and chemical 

 environment, rather than creators of environment. In the long 

 run, they may cause profound changes in environment, but the 



