Geology of Peoria County. 21 
The dip of the strata indicate a lifting up somewhere to the southwest of 
our county limits. This is all I know of the disturbances of the strata. They 
lie conformably upon one another, and upon the strata below them. 
THE PRAIRIES. 
“From the earliest knowledge of our prairies, speculation has been rife as 
to their origin.””’ Many hypotheses have prevailed as to the cause of their 
treelessness. I will name some of them. The burning of the grass by the 
Indians. The dryness of the atmosphere. The excessive moisture in early 
times. The fineness of the soil. And finally, the one more generally accepted 
at present, their lacustrine origin. But if, as we suppose, it was through the 
agency of the waters of this lake, the long continued floods, while running 
off, carried away so much of the drift,. leaving a surface of pure clay, sand 
and gravel; this theory is also wanting in a good basis. 
The fact that we have natural forests, that trees will grow when planted 
upon the prairies, shows the inadequateness of any of these theories to give a 
good reason for the phenomenon. 
I can see, however, reasons why the burning droughts we often have, and 
the prairie fires, would materially retard the growth of the forests. Our 
arboral growths are found mainly upon the margins of the streams; we see 
also, the showers often following only their course, giving a greater amount of 
precipitation to their valleys and bluffs. 
SOILS. 
Our soils are composed mainly of clays, sands, and vegetable mould. The 
salts derived from these, in solution, constitute the food for the plants. How 
did the vegetable mould get to the depth we find it on our high, level prairies? 
It can be accounted for, only in part by the work of the gophers, ants, etc. 
When I became acquainted with the observations of Charles Darwin on the 
work of the earth worm, in which he found in a certain locality (where there 
was probably unusual activity among them), they brought to the surface, 
three inches of earth during an interval of ten years. I was at once satisfied 
that to them we are indebted mainly, not only for the mixing of our soil con- 
stituents, but for another very important consideration —the porosity of the 
soils, without which it would have been almost impossible to cultivate them. 
THE FAUNA. 
I will mention the fauna of the carboniferous period, for in that only have 
I made collections in this county. The fishes of the Devonian still remain, 
and also newer and higher types appear. It was during this time, air-breath- 
ing animals began to appear. At first a fish like, semi-amphibious batrachian, 
named Archegosaurus, which had lungs. And also followed a smaller one. 
“From these creatures the other coal reptiles diverge, and ascending along 
two lines of progress, the one leading to the gigantic crocodile-like animals, 
provided with powerful jaws and teeth; the other leading to small, delicate 
and lizard-like species, living on land and feeding on insects and similar 
creatures.” | 
It is supposed there were nearly thirty species of these reptiles that devel- 
oped during the coal period, advancing to higher orders, as the air became 
purified. No remains of them have been discovered in the county. 
Of invertebrates we have many forms. Many of those collected are new and 
unnamed species. : 
I append a classified list of those I have found which are described and 
named. 
