CHAPTER IV. 



SLATE AND SHALE. 



Slate is one of the great commercial 

 products of the world. As far back as the 

 year 1877 the output of slate was not less than 

 1,000,000 tons per annum. The chief use to 

 which slate is put is for covering buildings, 

 and for this purpose it is better than any other 

 known material. It is also used in the con- 

 struction of billiard tables and for writing- 

 slates; these latter uses are very insignificant 

 as compared to its use in architecture. Slate, 

 like building-stone and limestone, is quarried 

 from the earth's crust and is found in the 

 strata close above the Metamorphic rocks, near 

 the beginning of what is called the Primary, 

 or Paleozoic period. As compared with the 

 coal formations it is very, very old. 



There are different substances called slate 

 that are not slate in the scientific use of that 

 word. In general all stone formations are 

 called slates that split up into thin layers. 

 But the true slate is a special material which 

 is formed by special processes of nature. The 



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