Geology of Peoria County. 17 
It was probably macerated in the warm waters so long, that it was reduced 
to a pulpy mass, from which was leached the potash and other soluble salts, 
leaving little else than the carbon and pitchy bitumen, which were insoluble, 
and into which also was infiltrated, in solution, the iron, sulphur and other 
impurities we find in it. 
It is estimated that it required ten feet of this carbonaceous matter, to 
make one of our bituminous coal. 
Finally, there comes a more rapid, and deeper submergence. Now also come 
the waters in swift, surging currents, laden with mud brought from distant 
and higher regions. This, settling down upon the stratum of carbonaceous 
material, formed by intermingling with the upper and looser portions of it, 
the bituminous shales and slates, which made a covering to the coal seams, and 
protected them from the grosser materials which were subsequently superim- 
posed upon them. 
The pressure of these limestones, clays, sands, gravels, etc., which were 
deposited upon them; the high temperature which still inhered in the earth 
below, and the great length of time, resulted in the formation of coal as we 
now have it. 
“Boussingault calculates that luxuriant growth of vegetation at the pres- 
ent day, takes from the atmosphere about half a ton of carbon per acre annu- 
ally, or, fifty tons per acre in a century. Fifty tons of coal spread evenly 
over an acre of surface would make a layer of one-third inch. But suppose 
it to be half an inch; then, the time required for the accumulation of a seam 
of coal three feet thick, would be seven thousand two hundred years. 
The first seam formed is called No.1. Upon this was deposited, first, dark 
sandy shale twenty-five feet, showing that there was carried in, fine sand which 
settled down between the loose parts of the wood to a depth of twenty-five 
feet and formed a compact shaly mass. But the sand continued to come in 
and above that we find five feet of fine-grained, compact sandstone. Then 
comes a mixture of clay and the pulverized shells and skeletons of sea ani- 
mals, which formed six feet. of nodular .argillaceous limestone. Then comes 
again the sand, and four feet more of sandstone was formed. Now comes again 
a mixture of clay and sand, and thirty-four feet of very hard, sandy, argilla- 
ceous shale results. Upon this was laid an impure clay, which made twenty- 
five feet of clay shale. And finally, upon this a comparatively pure clay, and 
we find nine feet of fire-clay; making deposits of one hundred and eight feet 
before we come to seam No. 2. 
There seems to be some discrepancy in the records of the strata between 
Nos. 2 and 3 from the sections we get from borings. But a very close approx- 
imation makes the deposifs about ninety-two feet, of much the same material 
and order as those below, though they vary in different localities. 
The next series, between 3 and 4, attain a thicknes varying from fifty to 
seventy-five feet, the next forty to forty-five feet, and above No, 5, thirty-five 
feet. Above No. 6 thirty feet, and soon the beds becoming thinner as we 
pass upward. ee 
These beds, as I have said, vary in different parts of the county. The 
measures dip to the east and north, some three feet to the mile. This makes 
the combined thickness of the strata seventy-five or more feet greater, conse- 
quently coal No. 1 is seventy-five feet deeper on the eastern than the western 
limits of the same. 
FIRE CLAY. 
It will be readily seen, that limestone of itself, gravel and gravel tonglom- 
erates, sand and sandstones, are not very largely endowed with plant food; 
and, although all other things might have favored plant growth at different 
times during the intervals in which these interdeposits were made, yet they 
had to wait the arrival of the clay beds before the flora again revived. 
