COAL. 107 
vat ion at the point in question. The approximate interval to be 
added can be estimated in various portions of the quadrangle by 
means of the table on pages 105-106. Where no measurements have 
been made in the vicinity the average interval should be used. 
TniCKNESS. 
In thickness the Waynesburg coal is variable, running from a few 
inches to 7 feet. Like the Pittsburg bed, it usually occurs in more 
than one bench, separated by clay partings. In general there are 
three persistent benches of coal. This is illustrated in PL VI. With 
few exceptions the upper fire-clay parting is persistent, with an average 
thickness of 1 foot, occurring in general a little nearer to the top than 
to the bottom of the seam. The bench directly below this is the one 
most commonly mined. 
Along the several branches of Pigeon Creek many country banks 
have been opened on this bed, and these show sections varying from 3 
to 7 feet in thickness (PL VI, sections 22 to 42). The table on the 
next page gives the exact measurements of these. 
