SOLIDIFIED SUNLIGHT. 151 



regenerated ; this is the very sunlight which became latent in 

 vegetable cells so long ago. It is locked-up sunlight set free 

 after a long imprisonment. It is the wasting sunlight of an 

 age when its blessings were not appreciated, packed away and 

 preserved to an age when man should dwell on the earth to 

 appreciate its uses and make it an agent of exquisite comfort 

 and high civilization. 



There are several varieties of coal ; let us look them over. 

 Perhaps you will smile when I tell you that the plumbago of 

 your pencil is essentially carbon. So it is. All your pencil- 

 ings are strictly " charcoal sketches." We can take common 

 coal and by subjecting it to pressure and heat while excluded 

 from the air, convert it into something much like plumbago. 

 It often occurs in iron-furnaces. This is sometimes called 

 black lead ; but it contains no lead ; its more appropriate name 

 is graphite. It is found among the metainorphic rocks. 

 Whatever it was, it has been pressed and baked and boiled 

 through the same processes which have so transformed the 

 original Eozoic sediments. Since graphite can be prepared 

 from coal, we may safely assume that graphite is only meta- 

 morphic coal. Indeed, there are regions where graphite occurs 

 in the same formation which in other regions we know as 

 Coal Measures. But the strata are all metamorphic. Most 

 graphite, however, belongs to a remoter geological age. We 

 find it in Vermont and most of the New England States ; 

 also in northern New York and many other American and 

 foreign localities. It can only be burned at a high tem- 

 perature. 



Next in respect to hardness and difficulty of combus- 

 tion is anthracite. This breaks in irregular lumps, with shin- 

 ing surfaces, and burns with only a feeble bluish flame. It 

 has a relatively high specific gravity, and furnishes more heat 

 per ton than any other species of coal. Anthracite is found 

 in situations where it appears to have been subjected to a 

 baking and hardening process which has driven off most of 

 the volatile hydrocarbons found in other coals. In the United 

 States, south-eastern Pennsylvania is the chief anthracite 



