Williams.] WHITE ON PENNSYLVANIA STRATA. Ill 



tbe Venango group in this report are the "Middle Devonian rocks 

 (Chemung, Girard, Portage, No. VIII.)" They are composed of— 



Feet. 

 Chemung 385 



Girard shales 225 



Portage Hags 475 



Mr. White considered the interpretation of the Venango group in 

 Erie and Crawford Counties as of great importance. He said : 



This identification [of the third Venango oil-sand with the LeBcouf conglomerate] 

 I account the most important discovery to which my survey of the district has given 

 rise. 1 



1 



The importance of the correlation is further testified to by the State 

 geologist, J. P. Lesley, who in his letter of transmission wrote : 



The cost of this survey has been justified merely by one result (setting aside the rest), 

 namely, the determination by sufficient evidence that the third oil sand of Venango 

 County is the quarry rock of Erie County, and that this deposit in crossing Erie 

 County changes its character from a muddy sandstone in the western townships to a 

 coarse gravel rock east of LeBajuf Creek, becoming the Panama conglomerate in the 

 State of New York ; everywhere charged with a peculiar group of fossil shells and 

 seaweed, and with petroleum, which has evidently resulted from their decomposi- 

 tion. 2 



The method of this determination was in the first place physical and not 

 by fossils. The average dip and direction of dip were ascertained by 

 the comparison of altitudes of the third oil sand in the numerous wells. 

 With this assumed rate of rise on going northward, outcrops were iden- 

 tified by their altitude ; these were followed from ravine to ravine or 

 quarry, and the rocks in the quarries were then defined, their fossils 

 identified, and thus their position m the chronologic scale determined. 

 Although the same method was practically used by both Mr. White 

 and Mr. Carll, when their tracings of correlation had reached Chau- 

 tauqua County the result was that Mr. White correlated the Panama 

 conglomerate with the third oil sand of Venango County, while Mr. 

 Carll placed it entirely below his Venango oil group. 



The fact seems to be, as we review the records of the survey, that 

 the data of lithologic character of rocks and of thickness of the deposits 

 were so constantly variable that the " theory of persistent parallelism 

 of strata" was little more than a theory, the exceptions to which were 

 as numerous as the illustrations. It was a cut-and-try system of 

 matching together innumerable sections, made up of irregular combi- 

 nations of shales, sandstones, conglomerates, and limestone of various 

 color, thickness, and texture. Whenever the gaps were over a mile or 

 two long the adjustment of the theoretical dip, a few feet more or less 

 to the mile, would enable the parallelism to fit any particular stratum 

 in a given section. The fact that those who showed evidence of having 

 noted the fossils, although they may not have identified them, were 



iQSp.101. »Q 4 ,p.VH. 



