32 THE CRUST WE DWELL UPON. 



of our planet the foundation of all geographical diversity, 

 the diversified habitat of plants and animals, the scene of 

 man's own life-labours, and the storehouse of those mine- 

 rals and metals upon which his civilisation and progress are 

 so intimately dependent. The study of its structure is 

 replete with intellectual interest of the most exalted de- 

 scription. The variety of its rock-formations, the minerals 

 and metals they contain, their modes of aggregation, and 

 the curious changes to which they have been subjected in 

 their repeated alternations from sea to land and from land 

 to sea, are all calculated to excite our interest and increase 

 our admiration of the means employed by the Creator to 

 alter, to diversify, and to sustain. And that interest and 

 admiration are increased a hundredfold when we perceive 

 in these formations the nature of the life that has preceded 

 us rising through long ages from the simple to the more 

 complex, from the simply sentient to the intellectual and 

 reflective, and this through forms so countless and varied, 

 and yet all belonging to the same great plan, that nume- 

 rous as are the existing forms of plants and animals, they 

 form but a tithe of those that have necessarily existed be- 

 fore them. No one, then, can look into the structure of 

 this crust without receiving newer and deeper insight into 

 the laws and ordainings of nature, and from all deeper in- 

 sight of nature the human intellect arises wiser, happier, 

 and more exalted. 



But the study of the earth's crust is not less desirable 

 from its economic advantages than from its intellectual in- 

 terest. Man's civilisation and progress, and his mastery 

 over the powers of nature, are intimately dependent upon his 

 knowledge and application of the minerals and metals. In- 

 deed, modem civilisation and progress have largely arisen 

 from this knowledge of the minerals and metals; and as 

 these hold determinate positions in the various formations 



