424 NEW YORK STATE MUSEUM 



barrels of oil a year has been obtained in the Ohio and Indiana 

 fields combined, in spite of determined attempts on the part of 

 the Standard oil company to curtail production by depressing the 

 price of crude oil below the point at which ordinary wells could 

 be operated. 



When the Ohio and Indiana fields were first studied, certain 

 facts were brought to light in regard to the Trenton limestone 

 that seemed greatly to restrict the promise which the announce- 

 ment that this limestone is an oil rock would carry. 



It was found that the petroliferous production was entirely 

 limited to the uppermost beds of the formation, generally to 

 the first 50 feet and never to more than 100 feet. It was farther 

 learned that the beds in question had suffered in their history 

 a change from true carbonate of lime to magnesian limestones 

 or dolomites, and that the porosity of the limestones as attested 

 by its holding gas, oil or salt water, was altogether dependent 

 on this chemical change, beginning where it began and ending 

 where it ceased. In other words, the dolomite corresponded ex- 

 actly to the " oil sand " or " pay-streak " of the great petroliferous 

 sand rocks in which we had hitherto found the principal stocks 

 of oil and gas. The explorers of the new field all came from 

 the old field and the identification referred to was universal. In 

 composition the oil rock was in many instances found almost 

 typical dolomite. 



That the dolomite was not the original substance of the rock 

 but a product of replacement was made evident from two lines 

 of facts, namely: first, small insulated areas of true carbonate of 

 lime that are sometimes found in the midst of dolomite districts; 

 and, second, fragments of the oil rocks brought up by the explo- 

 sion of torpedoes which show it to have been originally a crinoidal 

 limestone. A stratum of this character must necessarily have 

 been at the outset a true lime rock. 



Farther, it was soon found that the productiveness of any por- 

 tion of the field could be gaged with fair accuracy by knowing 

 the thickness of the dolomite. It was also established that the 

 areas within which the change had been accomplished were com- 

 paratively small and exceptional and that the great bulk of the 

 Trenton limestone remained in its normal state, having a compo- 



