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 fossiliferous 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 sedimentary 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 Füchsel (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 mountains; also that some formations have only marine fossils, 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 Füchsel 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 Füchsel showed that there was a definite order and process in the formation of the earth’s crust, their example was barren of followers until the beginning of the eighteenth century. _Wernerian Geology or Geognosy._—We come now to the time of Abraham Gottlob Werner (1749–1817), who from 1775 to 1817 was professor of mining and mineralogy in the Freiberg Academy of Mines. Geikie, in his most interesting Founders of Geology, says that Werner “bulks far more largely in the history of geology than any of those with whom up to the present we have been concerned—a man who wielded an enormous authority over the mineralogy and geology of his day.” “Although he did great service by the precision of his lithological characters and by his insistence on the doctrine of geological succession, yet as regards geological theory, whether directly by his own teaching, or indirectly by the labors of his pupils and followers, much of his influence was disastrous to the higher interests of geology.” Werner arranged the crust of the earth into a series of formations, as had been done previously by Lehmann and Füchsel, and one of his fundamental postulates was that all rocks were chemically precipitated in the ocean as “universal formations.” For this reason Werner’s school were called the Neptunists. Nowhere, however, did he explain how and where the deep and primitive ocean had disappeared.