336 THE CHANGING GENERATIONS 



his ideas eventually exerted was brought about by two other men, John 

 Playfair and Sir Charles Lyell. In 1802, Playfair published his Illustra- 

 tions of the Huttonian Theory of the Earth, in which the uniformitarian 

 thesis was further explained and developed, and documented with numer- 

 ous detailed and concrete examples. Catastrophism held sway for another 

 30 years, until LyelFs Principles of Geology (1830 to 1833) converted 

 most geologists to uniformitarianism. Lyell, the founder of modern 

 geology, at the age of sixty, was one of the first to accept Darwin's 

 ideas about evolution. 



The length of geologic time. Hutton, Playfair, Lyell, and the other 

 men who helped to create the modern science of geology all served to 

 prepare the way for the establishment of evolution as a fundamental 

 biological principle. So long as earth history could be supposed to have 

 comprised only a few thousands of years, or so long as men could take 

 refuge in the idea that sudden departures from the "order of nature" 

 were possible, the mind could still accept a belief in special creation 

 without too much strain. But the establishment of uniformitarianism 

 changed all this. Since, according to this principle, small and slowly 

 acting forces have worn away mountains and filled up the seas with their 

 debris, it must follow as a necessary corollary that geologic time has been 

 immensely long. In our own day we have become inured to the incom- 

 prehensibly huge figures used by the modern astronomer and geologist 

 in relation to space and time, and it is hard for us to realize the shock that 

 it was to an earlier generation, accustomed to thinking in terms of mere 

 hundreds or thousands of years, to find that the world was so immensely 

 old. Hutton himself was awed by the vista that his studies had revealed. 

 In his own words: 



When, to a scientific view of the subject, we join the proof which has been 

 given that in all quarters of the globe, in every place upon the surface of the 

 earth, there are the most undoubted marks of the continued progress of those 

 operations which wear away and waste the land, both in its heighth and in its 

 width, its elevations and extensions, and that for a space of duration in which 

 our measures of time are lost, we must sit down contented with this limitation 

 of our retrospect, as well as prospect, and acknowledge that it is in vain to seek 

 for any computation of the time during which the materials of this earth have 

 been prepared in a preceding world, and collected in the bottom of a former sea. 



The idea that geologic time has been very long, so revolutionary in 

 those days, has now become a textbook commonplace. Although to 

 Hutton the attempt to measure geologic time seemed vain, men have 

 by now succeeded even in doing this. By combining all that astronomers, 

 physicists, chemists, and geologists have learned about the subject, 

 it has been determined that the earth was born from the sun, probably 



