MINERALOGY. 501 



tween its elementary particles greatly to exceed its 

 material parts. 



Iron and Gold. 



By what mysterious law of nature does it happen, 

 that gold abounds and iron is scarce in all the equa- 

 torial regions, and the reverse is true in the temperate 

 zones. 



The Wicklow Mines. 



A piece of gold picked up in a bog in Wicklow 

 weighed 22 ounces, and was sold on the spot for 68 

 guineas. It weighed eight ounces more than the 

 heaviest piece ever got in one lump in South America. 



The Wicklow mine was simply a stream work, in 

 which the gold was dispersed in the form of small 

 pebbles and sand, through a bed of gravel, it was 

 consequently soon exhausted. 



Crystallization. 



Every substance in crystallizing, has a tendency to 

 assume a particular figure. Common salt crystal- 

 lizes in cubes ; Epsom salt in six-sided prisms ; 

 alum in octahedrons ; sugar-candy in oblique four- 

 sided prisms with wedge-shaped summits. 



The new theory of crystallization depends on 

 another, now universally recognized, that of definite 

 proportions. 



Rock Salt. 



The most obvious hypothesis respecting the for- 

 mation of rock salt, is that which supposes it was de- 

 posited by the sea, or by the desiccation of salt lakes, 

 which formerly covered the present continents. Salt 

 strata also diminish in thickness as they recede from 

 the sea. 



The objections are, that rock salt is much more 

 pure than the contents of sea water, which contains 

 muriate and sulphate of magnesia, sulphate of soda, 



