NATIONAL POWER AND COAL 159 
varying degrees of completeness) free from all other 
matter, save for the mineral veins, partings, etc., which 
are local impurities,” as are the quartz veins in a nugget 
of gold. Itis to be noted that unless the plant substance 
is sufficiently free from other matter to be substantially 
a deposit of plants alone, it is not a coal; but impure 
coals may grade into oil shales and a variety of other 
deposits. There are many varieties of coal which really 
merit separate consideration, but though cannels, 
anthracites and the others have their commercial im- 
portance and scientific interest, for the purpose of this 
lecture I shall generally mean by “ coal’? the most 
important and most widely used ‘ bituminous” coal 
of the household and factory. 
I do not wish to mislead you into thinking that my 
definition represents a universally accepted view of coal, 
but I believe it will be the generally accepted view when 
sufficient time shall have elapsed after the completion 
of certain researches now in progress. At present 
there is in the air a vague idea that coal is in some way 
due to plants, but they are widely supposed to be 
mineralised plants. Prof. Lebour in the recent British 
Association discussion on coal said: “ Geologists regard 
coal as a rock’’; and it is widely called a “‘ mineral,” a 
“ rock,’”’ a “‘ stratified rock,” or other term, which con- 
veys to ordinary people the suggestion that it is a stone 
of some sort. In the older books black coal, such as 
we use in this country, is always spoken of as “‘ stone 
coal.’” On the other hand, some experts, influenced 
still by Frémy, tend to-look on coal as he did, as 
a structureless, hardened jelly. Shakespeare asked: 
“‘What’s in a name? ”’ and I would answer, that it is 
