148 
DISCOVERIES OF COAL. 
is not absolutely confined to any one geo¬ 
logical formation, but is present to some 
extent in nearly all, yet there is one series 
of rocks in which it greatly predominates. 
'Y\\e great deposits of fossil fuel, are all of 
the same geological age, as estimated by the 
rude but certain chronology of the sequence 
of rocks. 
The geological term for the series of 
limestone, sandstone, and shale, rocks, and 
clays, which lie over the old red sandstone, 
or inferior systems, and under the new red 
sandstone, or superior strata, and which 
usually contains subordinate beds of coal 
and ironstone, is coal measures and this 
though in some instances (as in North 
Devon) no true coal is found in them. The 
terms coal field, coal basin, are expressive of 
the same area, but popularly restricted to 
the locality whence coal is actually obtained. 
The progress of steam navigation, by 
inducing careful search for fossil fuel, has 
been the occasion of its discovery in most 
parts of the globe. Every year additions 
are made to the long list of its localities. 
The history of science continually records 
