CAUSES IN THE FORMATION OF COAL. 115 



is admitted to vegetables, much of the carbon is separated in the form 

 of soot or lamp-black ; and this would seem to characterize, more es- 

 pecially, the smutty bituminous coals. If the oxygen is not sufficient 

 to consume the hydrogen, other compounds are formed, like coal-tar, 

 or naphthalin, as we see have been formed in coal beds in our western 

 states, running into pools or breaking out and overspreading fresh 

 water streams and ponds and often taking fire. 



The oxygen of the water of vegetables may have been evolved, as 

 one of the processes in the formation of coal and the inflammable por- 

 tion, hydrogen, remained. Woody fibre contains a proportion of hydrogen 

 which forms the inflammable principle of some coal, and the color of 

 decayed woody fibre show that both brown and mineral coal are the 

 results of vegetable decay and putrefaction. It loses at the same time 

 its powers of coherance, like linen exposed to heat and moisture, as 

 we observe in bituminous coal. The trunks of decayed trees are 

 found to have given off carbon, while the hydrogen has increased ; so 

 that the elements of the water in vegetables have united with the 

 wood and the carbon has united with oxygen and been disengaged. 



Liebeg says that coal in all its varieties possesses more hydrogen, 

 than wood, and less oxygen than is required to form water, this is 

 proof of what we have before said. The process of the disengage- 

 ment of carbonic acid still goes on at great depths in coal formations, 

 and hence its escape in what are called blowers ; and it is thought that 

 mineral springs from this circumstance, have become impregnated with 

 the gas. Gas often passes off in streams from beds of mineral coal. 

 This in volume is composed of 91.36 light carburretted hydrogen, 6.32 

 of olefiant gas and 2.32 of nitrogen gas, showing that changes in the 

 coal are constantly taking place. The decay and friable character of 

 the upper strata of coal beds is owing to the action of the air by 

 which the hydrogen is removed, and the coal is less combustible. 

 What is termed wood coal contains volatile oil, while the carburetted 

 hydrogen is found in connection with mineral, or anthracite coal. 



But among the primary causes which have contributed to the form- 

 ation of coal, is pressure. Coal is found in the carboniferous group 

 of secondary rocks including the red sand stones and the formations 

 of mountain limestones. The deposits are called coal measures; and, 

 from their form, coal basins, or coal fields. It is pretty certain that 

 these have been formed in beds of lakes and streams of fresh water, 

 and that they have, after a long interval, been thrown upward by the 

 internal action of heat, more or less violent in its effects. Other de- 

 posits were probably formed in the beds of large streams and in the 

 bottom of the sea, where the processes of their formation are still 

 going on. Over these have been gradually deposited innumerable 

 strata of sand and gravel, washed down during countless ages, in 

 which all have become consolidated and have slowly undergone the 



