"Slate Binders" of "Pittsburg" Coal Bed.—Gresleij. 363 
inch layers of slate in the pure coal. The Mississippi river is 
said to deposit an amount of detritus in one year found to be 
approximately equal to one of these thin binders, but then we 
are told most of this river material goes toward the augmen- 
tation or extension of the river's delta. But our coal shale- 
binders, as already pointed out, contain no signs of a typical 
delta formation. Flocculated particles are common to line 
river deposits. In these shales flocculation is not observed. 
Again, it is only reasonable to suppose that either of these 
shale-layers, whenever and however formed, was accumulated 
at one time, whether it took one year or ten years to do it; 
the process was uninterrupted, it operated uniformly both lat- 
erally and vertically. 
The "Pittsburg bed" contains several other binders or 
"dividing slates" besides the twins under consideration, but 
these are all of less persistent character and variable dimen- 
sions; they, however (so far as my examination has gone), are 
all practically identical in composition and texture.* though 
the degree of mottling may change locally ; thus everything 
points to a common origin and source of the materials of all 
the binders by which this splendid and unique coal-bed is 
horizontally and strati graphically divided, also a very similar 
mode of deposition or formation for one and all, whatever it 
was. Although apparently, perhaps, a not difficult coal-bed 
to explain geologically, a more close study of its stratiform 
composition extending over wide areas brings it, to my mind, 
Avell within the category of geological problems b} r no means 
as yet satisfactorily solved. 
The thickening of the "Pittsburg bed" is in a southeasterly 
direction, so also is that of the "bearing in" and other slates.. 
Thus the evidence goes to favor the assumption that both the 
organic material (the coal) as well as the inorganic (the 
"slates") had their source or chiefly depended upon or were 
largely governed by the land surface towards where the At- 
lantic ocean is now. 
Whenever the geologic history of this vast coal seam shall be 
something like correctly made out or described, there will be 
*Excep1 the bed of impure flre-clay <>r "draw-slate" of the miners, 
which lies immediately on top of the3 5 feet bench of coal already re- 
ferred to. 
