PALAEONTOLOGY AND GEOLOGY 



In their discussion of the geological changes of the 

 earth's surface, the Greek thinkers were quite free to 



assign an indefinitely long duration to the world and 

 to ascribe much importance to the slow action of ero- 

 sion by water, but, with the introduction of Chris- 

 tianity, the point of view was changed. All the varia- 

 tions must be condensed into a period going back 

 only four thousand years before Christ and the power 

 of the active agents must be speeded up correspond- 

 ingly. There, thus, grew up the idea that the slow 

 action of water was insufficient and that most changes 

 were due to the rapid action of heat as in volcanoes. 

 This explanation gave rise to the doctrine of cata- 

 strophic action in which the forces of nature became 

 more and more violent as one looked backward in 

 time. We can easily trace the development towards 

 our modern ideas of geology. There was, first, the 

 naive belief during the Middle Ages that in a single 

 week chaos was transformed into the earth as it is 

 now, except for minor changes such as are produced 

 by erosion and the limited action of volcanoes and 

 earthquakes. This may be called the static point of 

 view, and it would satisfy the mind until attention 

 was directed to the essential difference between ig- 

 neous and metamorphic rocks, and the great mass of 

 stratified rocks which point so certainly to the action 

 of water as a cause. It was also gradually established 

 that fossils were the remains of previously living sea 

 animals. These two facts were the conquerors of the 



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