732 COSMOS. 



vices in the geognosy of position I have treated more 

 circumstantially in another work.* Leonardo da Vinci, 

 towards the close of the fifteenth century, (probably when he 

 was planning the canals in Lombardy, which intersect the 

 alluvial and tertiary formations,) Frascastoro, in 1517, on the 

 occasion of the accidental exposure of rocky strata, con- 

 taining fossil fishes, at Monte Bolca, near Verona, and 

 Bernard Palissy, in his investigations regarding fountains, in 

 1563, had indeed recognised the existence of traces of an 

 earlier oceanic animal world. Leonardo, as if with a pre- 

 sentiment of a more philosophical classification of animal 

 forms, terms conchylia " animali die hanno I'ossa di 

 fuora" Steno, in his work on the substances contained in 

 rocks, (de Solido intra Solidum naturaliter contento,) distin- 

 guishes (1669) between (primitive?) rocky strata which have 

 become solidified before the creation of plants and animals, 

 and, therefore, contain no organic remains, and sedimentary 

 strata (turbidi maris sedimenta sibi invicem imposita) which 

 alternate with one another, and cover the first-named strata. 

 All fossiliferous strata were originally deposited in horizontal 

 beds. This inclination (or fall) has been occasioned partly 

 by the eruption of subterranean vapours, generated by 

 central heat (ignis in medio terra) and partly by the giving 

 way of the feebly supported lower strata. f The valleys are 

 the result of this falling in." 



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

 whilst Leonardo da Vinci, like Cuvier, regards the valleys 

 as the former beds of streams. 'j In the geognostic cha- 

 racter of the soil of Tuscany, Steno recognised convul- 

 sions which must, in his opinion, be ascribed to six great 

 natural epochs. (Sex suiit distinct^} Etrurire facies ex prse- 

 senti facie Etruria3 collecta3.) The sea had broken in at six 

 successive periods, and after continuing to cover the interior 

 of the land for a long time, had retired within its ancient 

 limits. All petrefactions were not, however, according to 



* Humboldt, Essai geognostique sur le Gisement des Roches dans 

 les deux Hemispheres, 1823, p. 38. 



f Steno de Solido intra Solidum naturaliter contento, 1669, pp. 2, 

 17, 28, 63, and 69 (fig. 20-25). 



t Venturi, Essai sur les Ouvrages physico-mathematiques de Leo 

 nard de Vinci, 1797, 5, No. 124. 



