GEOLOGY OF PEORIA COUNTY. 
READ BEFORE THE SCIENTIFIC ASSOCIATION, OCTOBER 22, 1886. 

BY WARREN H. CHAPMAN, M.D. 

EX-PRESIDENT. 
THE history of the structure of the earth’s crust in Peoria county, is the 
history of the same throughout the great Illinois coal basin, with very few 
local peculiarities. . 
As the geological formation of our county extends down to the primary 
rocks, and from whence commenced the building of this structure, so we will 
from that point, commence the study of its records, and take a hasty review 
of the genesis of the rocks, and the laying down the strata. ’ 
This is the beginning of time as measured by these phenomena.. For before 
this, there are revealed no data, by which we can measure time — no epoch 
by which we can discover a beginning or ending. Therefore to us, so far as 
our knowledge is concerned, its history must be relegated to the unnumbered 
zeons of the past. 
‘“‘Prof. Helmholtz has calculated, from the rate of cooling lavas, that the 
earth, in passing from a temperature of 2000° to 200 F, a temperature which 
will admit the growth of the simplest forms of vegetable life, must have taken 
350,000,000 years.” 
From the first time that man beheld the rocks, the question was forced upon 
his mind whence came they? Did they grow, or were they made as we find 
them? Let us give a few moments’ thought in answer to these questions. — 
From the time the crust of the earth became cool enough to make a some- 
what solid mass, disintegration began. The atmosphere was loaded with all 
the water, carbon, lime, sulphur, soda, and some other elements, which then 
existed upon the surface of the globe, in a state of incandescent vapor. This 
was constantly being condensed, and precipitated to the earth, to be again 
converted into vapor by the great heat of its surface. 
This process resulted in the disintegration of the soft, rocky mass; and as 
time progressed to a considerable depth. But in the course of time, the sur- 
face became so cool that the waters remained. Now begins the process of the 
formation of the stratified rocks. The heated waters, together with the salts 
held in solution, became a powerful solvent of these disintegrated particles. 
The surging and rushing of the undercurrents of the mighty oceans, were 
a potential force, grinding and pulverizing these loosened particles, to a greater 
or less degree of comminution. 
Then again, upon the shores of the seas, the ever restless waves, impinged 
with great force, grinding them, during all the ages, and carrying the detritus 
thus made into the wide oceans. 
And lastly, the air, the frosts, and the rains, had their share, in providing 
the material from which all the stratified rocks are made, excepting the lime- 
stones. 
Had it not been for these disintegrating agencies the crust of the earth 
would have been to-day one solid rock. | 
Now this material, having been deposited at the bottom of the oceans, was 
again formed into rock; some by simple mechanical pressure, others by chem- 
