Origin of Coal Measures Fire Clays. — Hopkins. 49 
The general order of occurrence is first the clay overlain by 
the ore, followed by the coal, but it frequently happens that 
one or more of these substances are lacking. Sometimes it is 
the ore, sometimes both the ore and the coal, and less commonly 
the clay. That is, in some places coal seams occur without any 
underlying clay, and in many places the clay occurs without 
any overlying coal. Again, it frequently happens that the clay 
may form one or more seams in the coal bed ; thus, in the fam- 
ous Pittsburg coal seam in southwestern Pennsylvania, and in 
West Mrginia, the inclosed fire clay seams, several in num- 
ber, are remarkably persistent and regular in thickness over 
wide areas. 
A\'e find some phenomena in connection with the occurrence 
of the fire clays, and the coal seams that are difficult to har- 
monize with the above outlined theory of origin. Thus, if the fire 
clay is the soil on which grew the vegetation that forms the coal, 
and in so doing changed the common clay to fire clay, how are 
we to explain (i) the occurrence of fire clay beds free from 
coal of any kind, (2) that such clay is frequently of better 
quality, that is, more refractor}- than that which is overlain bv 
coal, (3) the great thickness of some of the beds, and (4) the 
coal seams deposited on yellow shales or sandstones entirelv in- 
dependent of any fire clay ? 
( I ) Fire clay beds nut overlain by coal. — Comparativelv 
little is given on this point in the literature, but the observa- 
tions of the writer in several different coal basins lead him to 
think that this is a rather common occurrence. In Clearfield, 
Indiana, Westmoreland, Clinton, and Tioga counties, Pennsyl- 
vania, these coalless fire clay seams occur in considerable num- 
bers. 
The fire clay in these cases might have been formed in the 
usual way, and the absence of the coal explained by the fact 
that (a) the carbon might have been oxidized, owing to long 
exposure before the overlying sediments were deposited, or 
{b) the carbonaceous material may have been eroded before 
the deposition of the next stratum. ( e ) Another and, in some 
instances more probable explanation, is that the clay w^as fire 
clay before it was de])osited in its ])resent position, that is, it 
was changed to fire clay in some other locality and was then 
eroded and transported as sediment and deposited in its pres- 
ent position in nuich the same condition as it is at ])resent. 
