224 THE HISTORY OF GEOLOGY 



land consists, and in which the fossils lie embedded, for 

 it resembles in the most striking manner the ooze of the 

 sea-floor. In support of his argument Steno called atten- 

 tion to many interesting points of detail, such as the dis- 

 covery of a fossil pearl-oyster, with a pearl still sticking to 

 it : of fossil oysters perforated by galleries such as are 

 produced by boring worms ; and of another fossil shell, 

 covered with barnacles, which were adherent to its worn 

 surface, a fact from which he drew several ingenious 

 conclusions. 



Returning to the sediments in which fossils lie buried, 

 Steno pointed out that they are distributed in beds or 

 strata, which are frequently horizontal ; and he concluded 

 that the edges of each bed corresponded originally to the 

 margin of some sea, and its lower surface to the sea-floor. 

 In a series of beds all except the lowest were originally 

 contained between two planes parallel to the horizon. 

 In these statements there is contained implicitly the 

 modern doctrine of super-position i.e., that the order 

 in which beds succeed one another vertically in space is 

 the order in which they have been deposited, or the order 

 of their succession in time. This is explicitly stated by 

 Steno in another paragraph, " at what time there was 

 formed any Bed, the matter incumbent on it was all 

 fluid, and by consequence, when the lowest Bed was 

 laid, none of the upper Beds was extant." 



Steno, however, pursued his inquiry far beyond this 

 stage. He proceeded to point out that some strata 

 occupy an inclined or even vertical position, and he 

 rightly inferred that these must have been tilted out of 

 the horizontal by some natural disturbance subsequent to 

 their formation. 



The crowning triumph of Steno's achievement lay in 

 the application which he made of these conclusions to the 

 explanation of the structure of Tuscany. 



