144 COAL AND COAL-FORMATIONS. 



our main object will be to exhibit the points upon which 

 geologists are generally agreed, rather than to distract the 

 non-scientific reader with the minutiae upon which some of 

 them still continue to differ. 



What is coal 1 is a question more satisfactorily answered 

 by a little roundabout explanation than by a direct reply. 

 To say that coal is altered and mineralised vegetable matter 

 is true ; but the definition is too curt to be readily intelli- 

 gible. Every one knows something of peat and peat-mosses ; 

 well, this peat is simply coal in its first stage of develop- 

 ment. Were the peat-moss submerged and covered over 

 by deposits of mud and clay and sand, it would in course 

 of time undergo important chemical changes, by which 

 part of its gaseous contents (oxygen, hydrogen, &c.) would 

 be discharged, and the mass reduced to a compact coaly 

 substance known as lignite or brown-coal. Such brown- 

 coals are abundant in many countries (Germany, Austria, 

 New Zealand, &c.), and worked for economical purposes; 

 and were they subjected to still further changes they would, 

 in course of ages, become converted into shining stony coals 

 like those which are now raised so largely from the coal- 

 fields of Great Britain. The truth is, coal occurs in the 

 earth's crust in every stage of development, from the peat- 

 mosses and swamp-growths still in process of accumulation 

 on the surface, down through the tertiary brown-coals to 

 the bituminous stone-coals of the secondary and primary 

 periods, and from these again down to the still older non- 

 bituminous anthracites and graphites. All, in fact, have 

 had a similar origin. They are mere vegetable masses that 

 have undergone different degrees of mineralisation the 

 recent vegetable full of volatile matters, the lignites less 

 so, the bituminous coals giving off smoke and flame, the an- 

 thracites barely smoking, and the graphites masses of pure 



