A HISTORY OF SCIENCE 



of strata is never precisely the same in any widely sep- 

 arated regions. Nevertheless, there was a germ of 

 truth in Werner's system. It contained the idea, how- 

 ever faultily interpreted, of a chronological succession 

 of strata ; and it furnished a working outline for the 

 observers who were to make out the true story of 

 geological development. But the correct interpreta- 

 tion of the observed facts could only be made after the 

 Huttonian view as to the origin of strata had gained 

 complete acceptance. 



When William Smith, having found the true key to 

 this story, attempted to apply it, the territory with 

 which he had to deal chanced to be one where the sur- 

 face rocks are of that later series which Werner termed 

 secondary. He made numerous subdivisions within 

 this system, based mainly on the fossils. Meantime it 

 was found that, judged by the fossils, the strata that 

 Brongniart and Cuvier studied near Paris were of a still 

 more recent period (presumed at first to be due to the 

 latest deluge), which came to be spoken of as tertiary. 

 It was in these beds, some of which seemed to have 

 been formed in fresh-water lakes, that many of the 

 strange mammals which Cuvier first described were 

 found. 



But the "transition" rocks, underlying the "second- 

 ary" system that Smith studied, were still practically 

 unexplored when, along in the thirties, they were taken 

 in hand by Roderick Impey Murchison, the reformed 

 fox-hunter and ex-captain, who had turned geologist to 

 such notable advantage, and Adam Sedgwick, the brill- 

 iant Woodwardian professor at Cambridge. 



Working together, these two friends classified the 



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