Williams] CARLL, LESLEY. 115 



Iii western Pennsylvania the development of the oil industry fur- 

 nished a means of geological correlation not before accessible. The great 

 number of oil wells distributed over large areas in western Pennsyl- 

 vania (and since then wells have been drilled in almost every State in 

 the Union), where the records were preserved and studied, furnished 

 data of levels attained by particular formations under the surface. 



Mr. John F. Carll, one of the geologists of the second geological survey 

 of Pennsylvania, collected these data, coordinated them, and elaborated 

 from the records a classification of the formations. His results are con- 

 tained in Reports of Progress I, II, III, and IIII. 1 In the first of these 

 reports (I) the origin of the name oil sands is explained. In the early 

 drilling for oil in Venango County, the drillers, recognizing these sands 

 in their wells in Oil Creek, distinguished them by the term oil sands. 

 When the higher ground was perforated the sandstone layers supposed 

 to lie above the horizon of the three oil sands of Oil Creek were called 

 u mountain sands." 



Thus it came about that the series of shales and sandstones, afcout 

 350 or 400 feet thick, containing the three petroleum-bearing sands of 

 Oil Creek, Venango County, were named the " Petroleum Measures of 

 Venango, or Division of the Three Sauds or Oil-sand group," and the 

 rocks above, up to the base of the Conglomerate No. XII, were called 

 the " Mountain sand group or Barren oil measures." 



In this report the following equivalences were proposed: 



First mountain sand = Upper Berea grit, No. X. 

 Second mountain sand = Lower Berea grit? 



The fact of the conspicuous development of the three sand layers in 

 the wells of Venango County suggested the name "Venango oil-sand 

 group," which was definitely proposed and defended by Mr. Carll in 

 his third report. 2 



Prof. Lesley, in his letter of transmission, says of this report : 



The main feature of the report is the settlement of the true character of the Venango 

 oil-sand group as a distinct and separate deposit, with characteristic marks distin- 

 guishing it from the Paleozoic formations of a preceding and a succeeding age; the 

 differentiation of the group into three principal and other subordinate layers of 

 gravelly sand, holding more or less oil and gas ; the local variability of these sands; 

 their singular persistency beneath long and narrow belts of country ; their change 

 into barren shales elsewhere, and their independence of other oil-bearing sands and 

 shales of an earlier and of a later date. 3 



Mr. Carll proposed the name " Garland Conglomerate " for the low- 

 est member of the Carboniferous Conglomerate series in the part of the 



'I. Geol. Survey of Pennsylvania, Kept, of Progress: I. Report on Venango County, by J. F. Carll: 

 the geology Ground Warren, by P. A. Randall ; notes on the comparative geology of northeastern 

 Ohio, northwestern Pennsylvania, and western New York, by J.P.Lesley, 1875, pp. 127. 



II. Report of oil well records and levels in Venango, Warren, Crawford, Clarion, Armstrong, Butler, 

 etc., by J. F. Carll, 1877, pp. 398. 



III. Report on the Venango, Warren, Clarion, and Butler oil regions, by J. F. Carll, pp. 482. 1880. 

 1 III. Report on Warren County, by J. F. Carll, pp. 439. 1883. 



2 1 3 , p. 130. 



•Rept. of Progress, I 3 , pp. vi, vii. 



