18 ANNUAL REPORT 
THE ORDOVICIAN. 
In Ohio the upper half only of this great division needs be consid- 
ered. This has been divided by Orton as follows: 
Feet. 
3..>:Cincinnath series" .445 24 oe or ee 300—750 
QW ticaiShalesy. wise ce aoe eee Ee 0—300 
1. Trenton limestone (out-crop) .............. 0— 50 
The Trenton Limestone.—Quite the reverse, however, with the first 
member, known as the “Trenton Limestone.” Not only is this the most 
important source of oil in Ohio, but probably it is not excelled by any 
single formation in the world. It forms the floor, so to speak, of the 
entire state, being found wherever the drill penetrates to a sufficient depth. 
It outcrops only in one locality, viz., along the Ohio River, in the south- 
western corner of the state; but farther south, in Kentucky, it is the sur- 
face rock over a large area, and is the basis of the famous soils of the 
blue grass region. 
The composition of the Trenton has been made the subject of care- 
ful investigation by. Orton, who found that the oil and gas bearing beds 
are magnesian. ‘This is shown by the following analyses: 
Al,O.and 
CaCO, MgCoO, Insol. Res. PF @.0, 
Findlay gas rock......... 53.50 43 .05 1.70 1.25 
Bowling Green gas rock.. 51.78 36.80 4.89 ia 
Lima oil rock............ 55.90 38.85 75 2.94 
It was further found that in some places, at least, the magnesian 
character of the rock changes rapidly from the surface of the formation 
down. ‘Thus an analysis of the rock lying 100 feet below the top of the 
Trenton at Bowling Green showed over 88 per cent. of CaCO, and less 
than 7 per cent. of MgCO,; while, as shown above, the upper 
portion of the same formation has less than 52 per cent. of CaCO, and 
more than 36 per cent. of MgCO,. The magnesian character is import- 
ant, since it renders the rock porous, thus making it a suitable reservoir 
for the oil and gas. Outside of the producing territory in Ohio, the 
Trenton loses its magnesian character, the CaCO, composing usually at 
least 75 per cent. of the formation. 
The rock is often highly fossiliferous, and occasionally the pieces 
brought up by the sand pump are little more than a cemented mass of 
1Geol. Survey of Ohio, Vol. VI, pp. 103, 104. 
