HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



the seventeenth century. Steno begins his work on the earth's 

 crust by comparing fossil teeth found in the deposits of Tus- 

 cany with the teeth of living sharks. He then investigates 

 the origin of fossiliferous deposits and compares them with 

 unfossiliferous rocks. The latter, he says, were formed before 

 life existed on the earth, at a time when the earth was 

 enveloped in a universal ocean. Homogeneous and fine- 

 grained rocks represent, according to Steno, the primitive 

 earth-deposits which segregated universally from the undivided 

 ocean. If, on the other hand, a rock-stratum be composed of 

 particles varying in character and size, or if it comprise large 

 fragments derived from other rocks or fossil remains, such a 

 layer represents a partial deposit of later origin. 



Steno argued from the traces of salt and the presence of 

 marine animals, and even ship flotsam in certain deposits, that 



1 these had been formed on the sea-floor, whereas the presence 

 of a terrestrial fauna and of rushes, grasses, and the stems of 

 trees in other deposits, indicate that those had accumulated in 

 fresh-water basins. Steno was the first to enunciate definite 

 natural laws governing the formation of a stratigraphical suc- 

 cession in the earth's crust; these may be condensed as 



r follows : (i) a definite layer of deposit can only form upon a 

 solid basis; (2) the lower stratum must therefore have con- 

 solidated before a fresh deposit is precipitated upon it; (3) 

 any one stratum must either cover the whole earth, or be 

 limited laterally by other solid deposits ; (4) during the period 

 of accumulation of a deposit there is above it only the water 

 from which it is precipitated, therefore the lower layers in a 



-series of strata must be older than the upper. 



But Steno also realised that a series of strata originally 

 horizontal might become relatively displaced by subsequent 

 earth-movements. He cited examples of local crust-inthroiv, 



Steno had become a Roman Catholic, and his stay in his native city was 

 embittered by the enmity caused on account of his religion. He returned 

 to Florence, and was made Apostolic Vicar of Lower Saxony, dying in 

 Schwerin on the 25th November 1687. By command of the Grand 

 Duke Cosmo III. his body was brought to Florence and buried in the 

 Cathedral of St. Lorenzo. 



Steno's work, De solido infra soliditni naturaliter contento, was first 

 published in Florence (1669), anc ^ was intended merely as the prodrome of 

 a larger work, but no later work appeared. A second edition was printed 

 at Leyden in 1679, but the original text of Steno's little work is now a 

 bibliographical rarity; its contents are known chiefly through the i^edium 

 of Elie de Beaumont's French translation published in 1832. 



