232 HEROES OF SCIENCE 



forces are still destroying, by chemical decompo- 

 sition or mechanical violence, even the hardest 

 rocks, transporting the materials to the sea, 

 where they are spread out and form strata ana- 

 logous to those of more ancient date. Although 

 loosely deposited along the bottom of the ocean, 

 they become afterwards altered and consolidated 

 by volcanic heat, and then turned up, fractured, 

 and contorted." He showed that many hard 

 crystalline rocks, such as basalt, were of igneous 

 origin, and that some of them had been injected 

 in a melted state through fissures in the older 

 strata. He proved, by examining Glen Tilt, 

 that granite was once in a state of fusion, and 

 had cooled. He wrote : " In the economy of the 

 world I can find no traces of a beginning, no 

 prospect of an end," a declaration all the more 

 startling when coupled with the doctrine that 

 all changes on the globe had been brought 

 about by the slow agency of existing causes. 

 Sir Charles Lyell, writing on this, stated, " The 

 imagination was first fatigued and overpowered 

 by endeavouring to conceive the immensity of 

 time required for the annihilation of whole con- 

 tinents by so insensible a process ; and when 

 the thoughts had wandered through these inter- 

 mediate periods, no resting place was assigned 

 in the remotest distance. The oldest rocks were 

 represented to be of a derivative nature, the last 

 of an antecedent series, and that, perhaps, of one 

 of many pre-existing worlds." 



