492 C. SCHUCHERT CHRONOLOGY ON BASTS OF PALEOGEOGRAPHY 



eeedingly limited, did not hesitate to say that they were universal, and 

 that what was true of Saxony held for the entire world. This very erro- 

 neous idea of universal formations was destined to sway all suhsequent 

 stratigraphy, and it can not he said that geology has yet freed itself wholly 

 of Werner's dictum. Formations as now understood are more or less 

 localized deposits of sediments or solution materials, and even in the 

 sense that the term was understood by Werner — that is, as of period 

 value — it is not true that they are universal. To emphasize this, we need 

 only contrast the remarkably extensive Paleozoic marine sequence of 

 North America with the almost complete absence of such a record in 

 Africa south of the Sahara Desert. 



The first great advance in a determinable stratigraphy came with Wil- 

 liam Smith (1799-1801). lovingly nicknamed "Strata Smith," who 

 clearly pointed out that formations are characterized by definite kinds of 

 fossils that do not occur in other horizons. The time value of extinct 

 organisms was put into still better working order by Cuvier and Brong- 

 niart (1808-1811), whose work was based on that wonderfully interest- 

 ing Tertiary sequence of the Paris basin — a series of interbedded marine 

 and continental deposits. However, the full value of fossils as horizon 

 markers was not appreciated by them, because the theory of evolution as 

 taught by their associate Lamarck (1801) was set aside by them for that 

 of cataclysms, or the periodic destruction of all life and the re-creation 

 of similar but different successive floras and faunas. The once almost 

 universally accepted theory of special creations was long combated by 

 Lyell, and began to break down through the teachings of the French 

 geologist, Beaumont (1852), who pointed out that the periodic destruc- 

 tion of life was due to the sudden origin of mountains. In this explana- 

 tion arose the significance of unconformities, and gradually it was learned 

 that the cataclysms were local and not universal in nature, though the 

 full value of fossils as horizon markers was seen only after the appearance 

 of Charles Darwin's great classic, "The origin of species" (1859). 



During the nineteenth century nearly all geologists believed in the slow 

 and continuous emergence of the continents, and in North America the 

 dominant teaching was that of Dana, who held that the Paleozoic sea 

 gradually withdrew from North America, leaving in its wake progress- 

 ively younger, irregular rings of fossiliferous sediments that were de- 

 posited around the older Laurentian nucleus. This theory did not break 

 clown, even after it was shown that the nucleus could not have furnished 

 all of the sediments of the many formations, and one can not say even 

 now that the hypothesis of a continuous Paleozoic sea has vanished from 

 our text-books. However, as early as 1845 Murchison called attention to 



