iv PURSUIT OF KNOWLEDGE 77 



ways with the sole object of becoming intimately 

 acquainted with them. So long as the world shall last 

 his works will be an inspiration to naturalists, and an 

 exemplar of what can be accomplished by the observer, 

 however limited his worldly means may be, who seeks 

 for knowledge in the spirit of humility and truth. 



Most people are now familiar with fossil shells and 

 similar remains found imbedded in many rocks. Such 

 objects were known in very early times, and some 

 philosophers notably Leonardo da Vinci and Bernard 

 Palissy realised that they were the relics of life that 

 once existed at the places where the fossils were found. 

 It was generally believed, however, that marine shells 

 found inland were deposited there by the Deluge ; and 

 that strange animal remains were " freaks of Nature " 

 unworthy of serious study. An English land-surveyor, 

 William Smith, was the first to show, toward the end 

 of the eighteenth century, that fossils provide the key 

 by which the relative ages of the beds of rock which 

 make up the earth's crust can be determined. 



Before Smith commenced his work, fossils were sup- 

 posed to be scattered in haphazard fashion in the rocks. 

 As the result of many years spent in examining rocks 

 in all parts of the country, and collecting the fossils from 

 them, he was able to conclude that each stratum has its 

 own particular fossil population, and that the strata 

 lie upon one another in a regular order. Fossils were 

 thus shown to be the trade-marks of the rock-layers in 

 which they occur. This conclusion enabled a natural 

 system of classification of strata to be introduced, and 

 was the foundation of scientific geology. 



Rocks can be classified according to their appearance 

 or structure, but these features give no information as 

 to the period of the earth's history at which' the rocks 



