LITHOLOGIC CORRELATION IN BEND SERIES, TEXAS. 



15 



4,510 to 4,519 feet consists of normal shale of 

 the unit L tj'pe, apparently free from glaucon- 

 ite with the exception of one fragment, which 

 may well have come from above. The onh' 

 other trace of glanconite that could be found ui 

 that sample was in a minute fragment of crys- 

 talline limestone, which was full of it. The 

 basal glauconite bed is not everywhere directly 

 at the contact, but 9 feet is an unusually great 

 distance for the lowest glauconite bed to lie 

 above a contact. Moreover, the sample from 

 4,490 to 4,510 feet was estimated to contain 

 several per cent of white flint of the Ellen- 

 burger type. The relations do not seem en- 

 tirely normal. In the synthetic log a thin 

 glauconitic limestone deduced from the single 

 fragment found in the sample from 4,510 to 

 4,519 feet is represented, but this is evidently 

 very hypothetical. 



GENERAL CORRELATION WITH THE RECOG- 

 NIZED SUBDIVISIONS OF THE "BEND SERIES." 



The section in the Rudd well — a sharply 

 defined upper shaly succession from 2,215 to 

 about 2,522 feet (thickness 307 feet), a pre- 

 vailingly limestone succession from 2,522 to 

 2,962 feet (thickness 440 feet), aiul below this 

 to the top of the Ellenburger limestone again 

 prevailingly shale with a little limestone in the 

 upper part — is so similar to the generaU}- 

 recognized section of the '' Rend series" and the 

 Rudd well is so much nearer tlian the Seaman 

 well to the outcrop where tlie section was origi- 

 nally observed and named that the Rudd section 

 maybe taken as establishing the correlation with 

 the t.A'pe section. In other words, the upper 

 shale, with the probalile exception of the ]iart 

 above 2,245 feet, is the Smithwick; the middle 

 limestone is the Marble Falls limestone; and the 

 lower shale is the "Lower Bend" shale. By 

 means of the correlation proposed in this paper 

 these subdivisions can be carried to the Sea- 

 man well. 



A few of the facts thus brought out I'equire 

 discussion. 



Unit A evidently ])elongs to the Strawn, but 

 unit B is hard to place. If it lies immediately 

 above the Smithwick it should be the ecpiiva- 

 lent of what has sometimes been called the 

 "Millsap division." As oi'iginally described 

 by Cummins'" the "Millsap" is composed 



16 Cummins, W. F., Geology of norllnvestem Te.xas: Texas (ieol. 

 Survey, vol. 2, pp. 372-374, pi, (i, p. 361, 1S90. 



mostly of "blue [sandy?] and black [calca- 

 reous?] clays, with an occasional sandstone 

 and limestone and an occasional bed of sandy 

 shale. * * * At Thurber * * * the section 

 * * * was principally bluish claj% or, as 

 the miners call it, slate [calcareous shale?], 

 with a few seams of sandstone and limestone." 

 In a subsequent report " Cummins dropped the 

 name "Millsap," and stOl later'* he explained 

 that by tracing a coal bed of the Strawn forma- 

 tion to Millsap he had convinced himself that 

 the beds there were part of the Strawn. The 

 "MiUsap division" of Plummer'" Cummins 

 says "is not the same thing" as Cummins's 

 "Millsap division." Plummer defines his 

 "Millsap division" as the "beds between the 

 Smithwick shales and the top of the limestone 

 members outcropping in Parker County," 

 though without defining the precise top of the 

 Smithwick. He describes the "Millsap" as 

 consisting, in its best exposure, at Kickapoo 

 Falls, of thick, massive dark-blue shales with 

 lenticular, unevenly bedded limestones. It is 

 very interesting to note that he says that the 

 basal "Millsap" contains a light-colored quartz 

 sand which is in places separated from the 

 Smithwick by blue marls and thin limy layers. 

 That is to say, as appears in my synthetic and 

 percentage logs of the Seaman well, the maxi- 

 mum development of sand is somewhat above 

 the plane of most pronounced lithologic sepa- 

 ration. The same agreement with the results 

 presented in the synthetic log in this paper 

 appears in Plummer's statement-" that "in 

 places the black shale [of the Smithwick] 

 grades into a sandy blue and yellow-gray 

 layer above." Regarding the fossils Plummer 

 says that " the three lower limestones [of the 

 "Millsap division"] are found to contain a 

 fauna quite different from the overlying 

 Strawn beds," but also that it is the opinion of 

 Dr. R. C. Moore that the fossils "are much 

 younger than the Bend fauna." The extreme 

 disconformity between units A and B and the 

 seemingly slight disconformity if not transition 

 between iniits B and C as brouglit out in Plate 

 I would lead to the belief tiuit unit B, which I 



" Cummins, W. F., Note.s on the geology of northwest Texas: Texas 

 Geol. Survey Ann. Kept., vol. 4, p. 222. 1S!)2. 



'» Cummins, W. F.. Am. .Vssoe. I'eir. Geologists Bull., vol. 3, pp. 140- 

 147, 1919. 



1'* Plummer, F. IJ., Preliminary paper on the stratigraphy of the Penn- 

 sylvanian formations of uortli-cenlral Texris: Am. Assoc. Fetr. Geolo- 

 gists Bull., vol. 3. p. 140, 1919. 



M Idem, p. 139. 



