Xxxii Trans. Acad. Sci. of St. Louis. 
“oil showing” it makes when penetrated by the drill. If structural 
and other important geological conditions are favorable, however, the 
Trenton limestone is likely to be as important an oil producer in this 
territory. 
As the thin Coal Measures, the thick Sub-carboniferous, the thin 
Devonian and the thick Silurian formations that underlie St. Louis 
rise rapidly’ and outcrop to the west, the place to expect paying pools 
of oil and gas is to the east of St. Louis, in Illinois, where the strata 
flatten to a dip of ten feet per mile, where there are several anti- 
clinels, and where there are at least three different formations that 
are favorable for the occurrence of oil and gas in profitable quanti- 
ties. For Illinois has from 600 to 1400 feet of Coal Measures which 
contain several thick sandstones with heavy shale caps that are favor- 
able for oil reservoirs, and in which occur the oil pools of the eastern 
side of the state. At 600 to 800 feet below the Coal Measures occurs a 
black Devonian shale, beneath which an excellent grade of oil, 42° B. 
gravity, has recently been discovered at Peters, ten miles northeast of 
St. Louis. This horizon has seldom been tested in Illinois, as thus 
far the drilling has been mainly confined to the shallow Coal Measures. 
The Trenton and Galena formations underlie almost the entire 
state of Illinois and where they outcrop in the northwest corner of the 
state they consist of heavy, shale-capped limestones that are more or 
less magnesian, and, therefore, in a favorable condition for acting as a 
reservoir for oil. As they lie at a depth of 1500 to more than 2500 feet 
over most of the state, they are not likely to be tested until the upper 
sands have been exhausted. 
The structural conditions of Illinois are very favorable for oil 
and gas, as the state essentially consists of a large, simple basin, whose 
axis runs through the central portion of the state with a north-north- 
westerly trend. In fact, it is surprising that oil men have ignored 
the state until lately, as the conditions are most encouraging for the 
occurrence of oil and gas on both the eastern and western flanks 
of the basin. There is an abundance of material for forming, storing 
and protecting oil and gas and ideal conditions for its concentration 
into paying pools. A little oil and gas was found forty years ago at 
a depth of 400 feet at Casey, on the eastern flank of the basin, but 
the oil pools, that now exceed 80 in number and have been developed in 
six eastern counties, have all been discovered within the past three 
years. Since the eastern flank of the basin is being literally drilled, the 
oil men are beginning to give their attention to the western flank of 
the basin, where the conditions are fully as favorable. 
Prospecting on a limited scale has been started in several places 
and the edges of four oil pools have been located at Litchfield and 
Butler, in Montgomery County (fifty to sixty miles northeast of St. 
Louis), at Peters, in Madison County (ten miles northeast of St. 
®*The saccharoidal or St. Peters sandstone, which is 1452 to 1585 
feet deep in the Insane Asylum well, outcrops in the Meramec Valley, 
twenty-four miles southwest of this well, showing an average dip of 
about 60 feet per mile to the northeast. 
