EFFECTS OF COAL ON HUMAN INDUSTRY. 531 
gion of this coal field are abundantly loaded with 
nodides of argillaceous iron ore, and below these 
is a bed of millstone grit capable of enduring the 
fire, and used in constructing the furnaces ; still 
lower is the limestone necessary to produce the 
fusion of the ore. PI. 65, Figs. 1, 2. 
The great iron foundries of Derbyshire, York- 
shire, and the South of Scotland, afford other ex- 
amples of the beneficial results of a similar juxta- 
position, of rich argillaceous iron ore and coal. 
" The occurrence of this most useful of metals," 
says Mr. Conybeare,* '* in immediate connexion 
with the fuel requisite for its reduction, and the 
limestone which facilitates that reduction, is an 
instance of arrangement so happily suited to the 
purposes of human industry, that it can hardly 
be considered as recurring unnecessarily to final 
causes, if we conceive that this distribution of 
the rude materials of the earth was determined 
with a view to the convenience of its inhabi- 
tants." 
Let us briefly consider what is the effect of 
mineral fuel, on the actual condition of mankind. 
The mechanical power of coals is illustrated in a 
striking manner, in the following statement in 
Sir J. F. W. Herschel's admirable Discourse on 
the study of Natural Philosophy, 1831, p. 59. 
*' It is well known to modern engineers that 
* Geology of England and Wales, p. 333. 
