26 SCIENCE PROGRESS. 



out the man himself, and the argument is just as true of 

 sharks' teeth. Lest the great numbers in which the glosso- 

 petrse occur should be thought a difficulty — they were carried 

 away from Malta in bushels — he points out that every shark's 

 jaw contains sixty teeth in good working order, and these 

 as they wear out are continually replaced by fresh ones ; 

 further, he adds, sharks swim about in schools, so that a 

 great many teeth will generally be found bristling about in 

 the same place at the same time. Since sharks are very 

 voracious creatures, the multitude of glossopetrse implies 

 the existence not only of sharks, but of a whole world 

 of other animals, including those which live on cockles 

 and other shell-fish. That we next find Steno giving 

 serious attention to the study of cockle-shells is only 

 therefore what we might expect. He patiently traced the 

 manner of their growth, and ascertained, with a degree of 

 accuracy remarkable for those times, the minute details of 

 their structure. From the living cockle he turned to the 

 fossil shells, and by a careful comparison showed how they 

 agree, feature by feature, both in form and more particularly 

 in structure, with their modern representatives. This 

 structure, Steno insists, is the direct result of the manner 

 in which the shell is produced by the animal, and he con- 

 cludes that the fossil, like the recent cockle-shell, once 

 contained a living cockle inside it. 



Having thus, by close observation and strict logic, 

 breathed life afresh into these fossil remains, Steno pro- 

 ceeded to provide them with an environment : they were 

 bathed, he says, with an ambient fluid, which was none other 

 than sea-water ; hence it follows that the lands in which such 

 fossils occur, were once submerged beneath the sea. This 

 conclusion, he pointed out, is in complete harmony with the 

 nature of the material of which the 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 attention to many interesting 

 points of detail, such as the discovery of a fossil pearl- 

 oyster, with a pearl still sticking to it : of fossil oysters 

 perforated by galleries such as are produced by boring 



