944 Transactions of the American Institute. 



wood. Where the wood is covered by something which excludes the 

 oxygen, the loss of material goes on slowly, and the constituents react 

 upon each other, and after a time the wood changes its physical char- 

 acter, although it may perfectly retain its original form. In lignite 

 there has been a loss of some of the constituents of the wood, and 

 they have combined in a new form, making a decided approach toward 

 the condition of coal. Lignites exhibit all the different varieties that 

 we find in coal. In some places the transformation has been more 

 and in others less complete. This specimen from Alaska, where the 

 conversion into coal has progressed rapidly, has an appearance very 

 much like our carboniferous coal, although it is a modern formation. 



Cannel coals differ from other coals simply because the circumstances 

 of their formation have been different. Whatever remains you 

 find in cannel coal are typical of aqueous deposition. You will find 

 evidence, wherever the cannel coal is found, that there was formerly 

 an open lagoon, into which there was a leaching of the vegetable tissue 

 which sank to the bottom of the water, forming a carbonaceous mud, 

 which, daring the formation of the coal, was constantly saturated with 

 water. The cannel coals are rich in gas, which has a higher illumin- 

 ating power than that derived from other coal. 



The coals that can be burnecLin the open grate have lost a portion 

 of their volatile matter, but they contain the bitumen, and these are 

 the furnace coals so extensively used in the west. 



The next step is anthracite. When the material lias been exposed 

 to heat, the volatile matter has been more or less completely driven off. 

 and the residuum is a hard, flinty mass, which has been cemented 

 together by the action of the heat. Coke is the same, excepting -that 

 it has not been subjected to pressure, and the gases have exj)anded it 

 until it has become a cellular mass. 



Sometimes not only is the volatile matter all driven off, but . the 

 carbon itself is removed, and there remains a larger per centage oi 

 earthy matter than in coal ; and here we have a graphite tendency, 

 like this specimen, which is from Rhode Island, in which the coal ic- 

 so nearly converted into graphite that it is almost incombustible. 

 When the process is carried still further, the result is graphite, in 

 which all the bituminous matter and the greater part of the carbon 

 has been driven away, and the substance assumes a peculiarly brilliant 

 condition, with no oxygen, and generally a large per centage of earthy 

 matter. 



When herbaceous vegetation is acted upon by the conditions which 

 convert wood into coal, we have peat as the result. 



