18 



SHOKTER CONTRIBUTIONS TO GENERAL GEOLOGY, 102L 



It will not be worth while to go into a detailed 

 com])arison; the reader can make his owii on 

 the grajihic logs, hut a few of the larger simi- 

 larities and differences will he pointed out. In 

 the driller's log of the Seaman well at least part 

 of the true Smithwick shale might he recognized 

 in tlie hlue shale and slate ])etween 3,ir)0 and 

 3,430 feet, and the approximate limits of the 

 "Smithwick lime" hetween3,430 and 3,o90feet. 

 The a|)])roximate limits of the "Black lime" are 

 indicated between 3,760 and 3,870 feet. The 

 similarity of the u])per part of miit J to the 

 lower ])art does not a])])ear. My observations 

 indicate that the otdy basis for the identification 

 of "sand" between 4,190 and 4,200 feet is a 

 small amomxt of slightly sandy shale, most of the 

 material being ])ure black limestone. A])])ar- 

 ontly the driller mistook- flint for sand. The 

 "Lower Bend" shale is well defined, and the 

 distinctive blue-gray coloi' of the "Lower Bend " 

 limestone is brought out ])y the term "dark-gray 

 lime" a]i])lied to the material between 4,370 

 and 4,420 feet, as against "black-gray" a])])lied 

 to the Marble Falls limestone, though the u])])er 

 boundary assigned is 20 feet too low. The 

 essential fact I wish to em])hasize, liowever, is 

 that no matter how faithfully a log may rep- 

 resent the dominant lithology of any ])art of 

 the section jienetrated it is not likely to bring 

 out those facts which are needed for estal)lish- 

 ing an accurate correlation. I l^elieve that an 

 adequate basis for arriving at the stratigraphic 

 results needed in ])resent-day oil geology can be 

 furnished only by a gra))hic ]iercentage log, 

 which, milike even the best verbal or gra]ihic 

 log of the usual type, records not merely the 

 dominant rock but shows in ([luintitative terms 

 the ])ro])ortions within that rock of the ])rincipal 

 constituents, and, to sujiplement this log, the 

 determination of any characteristics or mate- 

 rials of special significance. 



GENERALIZED LOG AND POSITION OF OIL 

 SANDS. 



To summarize the results of the study of the 

 Rudd and Seaman wells the generalized log in 

 column 6, Plate I, has been prepared. The 

 thicknesses assigned to difTercnt parts of the sec- 

 tion are liased on average thicknesses in the 

 Ranger field, as reported by different writers.-' 



21 Reeves, Frank, unpublished report of the United .States Geological 

 Survey on the Ranger and Eastland fields and oral eommunieations. 

 Matteson, W. G., Central Texas oil fii'kls: Am. Assoe, Pctr. (ieolngists 

 Bidl., vol. 3, pp. 173-175, 1919. Plummer, F. B.. Penusylvaiiian forma- 

 tions of north-c-'entral Texas: Idem. pp. 13'.»-110. 



As the Ranger field lies between the two 

 wells the thicknesses used are also for the 

 most part intermediate between those in the 

 two wells. In this log thicknesses of certain 

 beds which I wished to emphasize, especially 

 of glauconite and sandy beds, have been very 

 much exaggei'ated. 



As the most inunediate object of this investi- 

 gation is to supply a framework for determining 

 extictly the stratigra]>hir position of oil horizons 

 in the "Bend series" in north-central Texas, I 

 have made an attempt to indicate in a general 

 way the possible position in my generalized 

 section of the oil sands recorded by several 

 geologists. The records I have used may be 

 summarized as follows: 



Reeves. 



[Op. cit. The numbers given to the sands in the generalized log, col- 

 umn ti, PI. I, in pocket, correspond to the numbers in tliis list.] 



1. •■Smithwick lime" ( P>reckenridge, Caddo, or False 



Ulack lime I. 



2. "Lower .Smithwick shale," 80 to ICO feet, above the 



■' Blaek lime. " 



3. Top of " lilack lime. " 



4. Second jiay, 70 to 130 feet below the top of the " Black 



lime. " 



5. McCleskey or Ranger .sand. 180 to -'-'0 feet below the 



top of the "Black lime. " Usually directly overlain 



by gray lime.stone. 

 0. Fourth pay, 270 to 300 feet below the top of the "Black 



lime. " 

 7. Fifth pay, 420 to 4(10 feet below the top of the "Black 



lime. " 



Matteson, 



|0p. cit., p. 192.) 



(o) Smithwick shale; oil and gas from lenticular .sands. 



(fc) C'ontaot of Smithwick and Marble Falls. 



(f) Fincher sand, about 9.5 feet below the top of the Marble 



Falls [Marble Falls equals "Black lime"?]. Really 



a sandy limestone. 

 (rf) (iordon sand (=Mc( 'leskey or Ranger sand?], 130 to 225 



feet below toji of the Marble I'alls. Overlain by 110 



to ItiO feet of gray lime. 

 (el Jones sand, 32.") feet below the top of the Marble Falls 



(Ranger field). 

 (J} \'eale sand (Caddo, Stephens County), 640 feet below 



the lop of the Marble Falls. 



Hill. 



[Hill, R. T., Petroleum in the Texas Bend series; Oil Trade Jour., 

 June, 191S, p. 88.] 



I. At Caddo, Stephens County, immediately below the 



top of the "Black lime." 

 II. South of Breckenridge, Stephens County, at less than 

 100 feet in the ["Black"] lime. 

 III. At Ranger, somewhat over 200 feet in ttie ["Black"] 



lime. 

 I\'. At the Morris ranch in Coleman County, in the iniilst 

 of black shale, over 200 feet below the bottom of the 

 black lime. 



