50 The American Geologist. juiy, 1901. 
(2) TJic clays that occur free from the coal seams are apt 
to be more refractory than those underlying coal seams. — It 
is a matter of observation that the most refractory clays in the 
Coal Measures are found among those which have no coal 
overlyingthem. This may be due partly to greater original purity 
and partly to a leaching subsequent to the elevation of the land. 
Thus the secondary deposition of the clay would tend to re- 
move a greater percentage of the soluble bases that form the 
fluxing constituents and after the elevation of the land the 
leaching by the meteoric waters would tend to still further re- 
move the soluble materials. The texture of clay is not favor- 
able to the rapid percolation of water, but the slow circulation 
through a long period of time may accomplish the same re- 
sult. The accumulation of the iron carbonate ("the ore balls") 
SO' abundant in some places, shows that the water does perco- 
late through the clay to some extent. Where the clay is over- 
lain by coal, the tendency is often the opposite to the above and 
iron is carried into the clay from the oxidizing pyrite in the 
overlying coal. 
(3) The great thickness of some of the clay beds. — In some 
places the fire clay deposits are thirty feet or more in thickness. 
One can hardly conceive how the vegetation growing on the 
top of a deposit of this thickness would extract the iron and 
the alkalies from the entire body of the clay. If it were formed 
in this way one would naturally expect the upper part to be the 
purest, and at least some considerable portions of the middle 
and lower portions to be unchanged. Instead we find, so far 
as there is any difference, that the lower part is likel}- to be 
the best clay and the poorest part at the top. 
At Bolivar, Pa., the flint fire clay is over twenty-five feet thick 
and overlying it between the clay and the coal there are several 
feet of shale. How would it be possible for the plants of this 
coal seam to leach out the iron and alkalies from twenty-five 
feet of clay when there are several feet of imchanged shale 
lying between them ? 
At Blossburg, Pa., there is a bed of fire cla}- 15 to 2^ feet 
thick, with no coal or carbonaceous matter associated with it, 
and no fossil plant remains in so far as known. The laminated 
structure of this deposit is additional evidence in support of 
the belief that the clay was fire clay at the time of its deposi- 
tion and not clav that has been changed in situ. 
