62 A CENTUBY OF SCIENCE 



Cosmogonists. Then came the expounders of the 

 earth's origin, the cosmogonists of the sixteenth to the 

 end of the eighteenth centuries. The fashion of this 

 time was to write histories of the earth derived out of 

 the imagination. 



Earliest Historical Geology. Even though Giovanni 

 Arduino (1713-1795) of Padua was not the first to 

 classify the rocks into three series according to their 

 age, he did this more clearly than any one else before his 

 time. The rocks about Verona he grouped in 1759 into 

 Primary, Secondary, Tertiary, and Volcanic. This 

 three-fold classification came into general use, though 

 modified with time. 



Early in the nineteenth century it had become plain 

 that formations of very varying ages were included in 

 each one of the three series. Through the study of the 

 fossils and the recognition of the fact that mountain 

 ranges have been raised at various times, causing 

 younger f ossilif erous strata to take on the characters of 

 the Primary, it was seen that these terms of Arduino had 

 lost their original significance. 



The first one to describe in detail a local stratigraphic 

 sequence was Johann Gottlob Lehmann (died 1767). 

 In 1756 he published "one of the classics of geological 

 literature," distinguishing clearly thirty successive sedi- 

 mentary deposits, some of which he said had fossils, but 

 he did not use them to distinguish the strata. 



What Lehmann did for the Permian system, George 

 Christian Fiichsel (1722-1773) did even better for the 

 Triassic of Thuringia, in 1762 and 1773. He pointed out 

 not only the sequence, but also how the gently inclined 

 strata rest upon the older upturned masses of the moun- 

 tains ; also that some formations have only marine fos- 

 sils, while others have only terrestrial forms and thus 

 indicate the proximity of land. The deformed strata he 

 thought had fallen into the hollows within the earth, 

 great caverns that had also consumed much of the 

 oceanic waters and had in so doing greatly lowered 

 the sea-level. It was Fiichsel who first introduced the 

 theory of universal formations, and who defined the term 

 formation, using it as we now do, system or period. 

 Even though Lehmann and Fiichsel showed that there 



