1830.] 



421 



[Ashburner. 



group, is sometimes thin, very fine, micaceous and muddy when taken from 

 the sand pump ; in this condition it seldom produces any petroleum. This 

 is the character of the sand at Pleasantville, where it contained only a trace 

 of oil. The black oil of this district came from what was known as the 

 stray or split third, occurring some 25 feet above the regular sand. Where 

 the Venango sands are formed in thin layers, fine grained and clayey the 

 driller views the territory with suspicion. 



Note. — It must be remembered in comparing the sands of the two dis- 

 tricts that they belong to different geologic formations. Based on lithological 

 and stratigraphical facts, I make the Venango oil sand group the equivalent 

 of the Red Catskill, No. IX (Old Red Sandstone), while the Bradford sand 

 is of Chemung age. 



The following general section shows their relative positions : 



Venango group, Catskill, No. IX. 



First sand 40 feet. 



Interval 105 " 



Second sand 25 " 



Interval 110 " 



I Third sand 35 " 



Chemung, No. VIII. 



I Interval 



I- Bradford sand. 



1000± 

 45' ' 



gee "Oil Sands of Penna.," Franklin Institute Journal, April 1878, also 

 "Bradford Oil District," Transactions American Institute Mining Engi- 

 neers, Vol. VII ; by the Author. 



The accompanying illustration shows a typical specimen of a good pro- 

 ducing third sand in the Venango group and a specimen of Bradford sand, 

 such as might be taken from any of the producing wells in the Northern 

 district. A productive Venango sand consists of a white, gray or yellow 

 pebble rock ; the pebbles being loosely cemented together and generally 

 bedded in fine sand. The rock is open and porous. The interstices be- 

 tween the pebbles and sand grains are extensive and capable of containing 

 a large bulk of oil ; but this character does not maintain itself over any 

 extended area. Areas of such sand are small and scattered and are sepa- 

 rated by sand beds, possessing a character belonging to the unproductive 

 sands. 



The Venango sands are not homogeneous over any considerable area and 

 are frequently very heterogeneous in section. The thickness of the sand 

 varies ; in one locality the upper part of the sand may be pebbly and of 

 productive character and the lower part fine and contain no oil, while but 

 a short distance away the conditions may be reversed. 



Such then are the principal features of the two great oil producing rocks 

 of Pennsylvania. 



