554 WESTERN COAL MEASURES AND INDIANA COAL. 
More especially are we led to doubt the equivalency; if we 
take into account the great preponderance of coal measure strata 
in the Pennsylvania district, which goes to show that the condi- 
tions necessary for the production of coal extended over a much 
greater period of time in the ies ae than in the western 
“field. 
Though I have assumed that the greatest depth of coal strata in 
the western measures will not exceed one thousand feet, in In- 
diana it will not be found greater than six hundred and fifty feet, 
including the Millstone grit. In a few localities in this State 
there are one or more very thin seams of coal below the Archime- 
des limestone, but no coal of any economical value has yet been 
s lower than the base of the Millstone grit. 
' There are in Indiana two well defined zones of coal, the east- 
ern and western zone, and though an equivalency in some of the 
seams is clearly traced, from one to the other, yet the quality of 
the coal is quite distinct in each. 
The area of the eastern zone is about four hundred and fifty 
square miles, or two hundred and eighty-eight thousand acres, and 
the included coals belong to the bituminous variety characterized 
as non-caking or free-burning. 
The cherry-coal or soft coal of England is a non-caking coal, but 
the non-caking coals of Indiana differ somewhat in physical struc- 
ture from the English coal and from a similar class of coals found 
in the Mahoning valley, Ohio, and the Shenango valley, Pennsyl- 
vania ; the latter two being the only other localities in the United 
States where non-caking coal is formed in any quantity. The 
Indiana coal from this zone has received the local name of Block 
coal; a name given to it by the miners on account of the facility 
with which it can be mined in blocks as large as it is possible to 
handle. The beds are crossed nearly at right angles by joint 
seams that greatly facilitate the operation of mining, which is us- 
ually carried on without resort to blasting. Blocks are taken out 
the full depth of the seam and leave a zigzag, notched outline, on 
the face of the mine, resembling a Virginia worm fence. 
Block coal has a laminated structure and is composed of alter- 
nate thin layers of vitreous, dull black coal, and fibrous, mineral 
charcoal. In the direction of the bedding lines it splits readily 
into thin sheets like a slate, but breaks with difficulty in the op- 
posite direction, and when struck with a hammer emits a sound 
