390 ILLINOIS STATE ACADEMY OF SCIENCE 



probable that oil and gas will be obtained from this 

 horizon. 



3. Niagara Limestoue. In a number of localities 

 small asphaltic residues have been found in the more 

 porous parts of the Niagara limestone, especially near 

 its top, and in certain places wells have encountered con- 

 siderable pockets of gas and sometimes a little oil in the 

 bottom of the drift and in the top of this limestone. In 

 places the oil is sufficient in amount to spoil water wells, 

 but has not been found in sufficient quantity for economic 

 use. Early reports of borings in the Niagara limestone 

 state that a few barrels of oil were obtained from that 

 formation. Locally a thin sandstone may occur at the 

 base of the Niagara, and this is a possible oil and gas 

 horizon. 



4. Maquoketa Shale, While this formation is com- 

 posed largely of clayey shales passing into impure lime- 

 stones, in a few horizons small carbonaceous layers have 

 been reported, and a few well borings have reported 

 some oil showings in these shales. 



5. Galena Dolomite. This heavy dolomitic formation 

 underlies the northeastern portion of the state and has 

 been penetrated by many wells. Only a few very meagre 

 oil showings have been reported from this horizon. How- 

 ever, in the northwestern part of the state, i. e., in the 

 upper Mississippi Valley lead and zinc district, at the 

 very base of the Galena dolomite is a peculiar chocolate- 

 colored shale known locally as the ''oil rock". This is 

 very rich in carbonaceous material, — in fact from it oil 

 and gas can be distilled and dry splinters of the shale 

 burn with a smoky flame. This peculiar carbonaceous 

 shale is confined mainly to the lead and zinc district and 

 exists, if at all, only in small quantities in the northeast- 

 ern part of the state. There is still a possibility, but not 

 a probability, that thicknesses of this material sufficient 

 to furnish small supplies of oil and gas may be found 

 in that part of the state. 



