50 WASTE AND RECONSTRUCTION. 



connections as a member of the solar system. Annual 

 revolution and daily rotation, daily and seasonal alternations 

 of heat and cold, currents and counter-currents of wind, 

 evaporation and rainfall, waves and tides, currents and 

 counter-currents of water, are all results of the earth's rela- 

 tion to the sun and her sister-planets. So in like manner 

 are the phenomena of vegetable and animal growth; so, 

 too, are many of those chemical and electro-magnetic activi- 

 ties with which science is but slenderly acquainted ; and so 

 also, perhaps, though in a remoter degree, that manifesta- 

 tion of internal vulcanism concerning which philosophy 

 can do little more than merely hazard conjectures. So 

 long, therefore, as the earth's primal relations endure, these 

 secondary forces must operate as a necessary consequence, 

 and thus the rocky crust must continue to undergo a round 

 of waste and reconstruction as ceaseless as the revolutions 

 of the planetary system, and as permanent in its power. 

 How harmonious the system by which this earth, in the 

 midst of all its mutations, is kept ever fresh and young ! 

 Day after day, and year after year, the aspects are cease- 

 lessly changing, but the vitality remains the same ; cycle 

 after cycle the forces may shift their direction, but their 

 power remains unimpaired. Everything around us being 

 seemingly stable, it may be difficult to realise this concep- 

 tion of incessant change, just as it is impossible to estimate 

 the lapse of time required for its fulfilment ; but an effort 

 must be made, and not till the mind has learned to form 

 some idea of the ceaseless mutations to which the earth's 

 crust is subjected, the causes by which these mutations are 

 effected, and the amount of time required for their produc- 

 tion, can it be said to comprehend the fundamental truths 

 upon which the science of geology is erected. 



