THE TJNIVEKSE. DISCOVERIES IN THE CELESTIAL SPACES. 347 



in his work on the substances contained in rocks, (de 

 Solido intra Solidum naturaliter contento) (1669), distin- 

 guishes "rocky strata (primitive?), hardened before the 

 existence of plants and animals, and, therefore, never con- 

 taining organic remains, from sedimentary strata (turbidi 

 maris sedimenta sibi invicem imposita), which alternate with 

 each other and cover those other strata first spoken of. All 

 deposited strata containing fossils were originally horizontal. 

 Their inclination has arisen partly from the outbreak of sub- 

 terranean vapours which the central heat (ignis in medio 

 terrse) produces, and partly by the giving way of lower sup 

 porting strata. ( 534 ) The valleys are the result of the falling 

 in, consequent on the removal of support." 



Steno's theory of the formation of valleys is that of Deluc, 

 whereas Leonardo da Yinci, ( 535 ) like Cuvier, considers the 

 valleys as formed by the action of running water. In the 

 geological character of the ground in Tuscany, Steno thought 

 he recognised revolutions which must be attributed to six 

 great natural epochs, (sex sunt distinctse Etrurise facies, ex 

 prsesenti facie Etrurise collectse) : at six recurring periods 

 the sea had broken in, and after continuing for a long time 

 to cover the interior of the country, had withdrawn again 

 within its ancient limits. Steno did not, however, regard 

 all petrifactions as belonging to the sea ; he distinguishes 

 between pelagic and fresh-water petrifactions. Scilla, in 

 1670, gave drawings of the petrifactions or fossils of 

 Calabria and Malta : our great zoologist and anatomist 

 Johannes Miiller has recognised among the latter the oldest 

 drawing of the teeth of the gigantic Hydrarchus of Alabama 

 (the Zeuglodon Cetoides of Owen), a mammal of the great 

 VOL. n. 2 A 



