16 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 102L 



take to be about equivalent to Plummer's 

 "Millsap division," should be eorrclated with 

 the Smithwick rather than with the Strawn. 



The presence of a limestone in the lower part 

 of the Smithwick in the Seaman well, instead of 

 the shale in the Rudd well, and of shale below 

 that in the top of the Marble Falls in the Sea- 

 man well, instead of the black limestone in the 

 Rudd well, has been discussed above (p. 10) 

 with reference to genesis but requires additional 

 comment with reference to nomenclature. 

 Frank Reeves, who has prepared a report to be 

 published by the United States Geological 

 Survey on part of the Ranger and Eastland oil 

 lields, tells me that in wells in that region a 

 "lime" called the "vSmithwiek lime" is rec- 

 ognized. It averages about 100 feet in thick- 

 ness, and its top lies pretty constantly 300 

 feet above the top of what is there called the 

 "Black lime," taken as the top of the Marble 

 Falls. Between the two lie shales called the 

 "Lower Smithwick shales." In the Seaman 

 well the relation of the limestone between 

 3,430 and 3,.'j<)0 feet (thickness 160 feet) iii the 

 driller's log or between 3,470 and 3,(il() feet 

 (thickness 140 feet) in the synthetic log and 

 the top of a sandy black limestone oi- calca- 

 reous black sandstone at 3,760 feet in both logs 

 (interval in driller's log 170 feel, in synthetic 

 log 1.50 feet) is so similar to the relation of 

 the "Smitlnvick lime," allowing for increase in 

 thickness at least of detrital nu'ml)ers in the 

 direction in which the Seaman well lies from 

 the Ranger field, that it seems justihahle to 

 assume that the limestone in the lower part of 

 unit C is the "Smithwick lime." Then the 

 "Lower Smithwick shale" is essentially the 

 equivalent of the to]i of the Marble Falls. 

 Whether paleontology would reveal this rela- 

 tionship is uncertain, as the fauna might be 

 more influenced by environment than by time. 



A consideration of thickness ratios in con- 

 nection with those tabulated on page 17 sup- 

 ports this interpretation. Thus, assuming the 

 Maii)le Fails in both wells to begin at the top 

 of unit L), we have: 

 I) to .1, Rudd 441 feet. Seaman 6S0 feet, ratio 



11. 



,i_ 



Or, assuming it to begin v.'itli the toi> of unit E 

 in l)oth wells, we hav(>: 



E to J, Rudd 344 feet. Seaman 534 feet, ratio 

 1: 1..55. 



Both of these conform to normal ratios. If w'c 

 assume that miit -D in the Seaman well corre- 

 sponds to the lower part of units C and C in 

 the Rudd well — that is to say, that it belongs 

 to the Smithwick — we have: 



D to J, Rudd, 441 feet; F^: to J, Seaman, 534 

 feet; ratio 1 : 1.21 , 



a very low ratio. Or, if we compare Smithwick 

 thicknesses, we have : 



C + C', Rudd, '275 feet. Seaman, 595 feet, ratio 

 1: 2.16, 



a high ratio; but assigning miit I) in the Sea- 

 man well to the Smithwick we have: 



C + (", Rud.l, 275 feet; (' to 0, Seaman, 741 

 feet; ratio 1: 2.7, 



which is the highest ratio between correspond- 

 ing units ui the two wells except that for unit Ci. 

 The Marble Falls limestone is so well defined a 

 fornuilion, except for the argillaceous luiit D at 

 the to]) and the limestone of unit K Ix^low it, 

 that its identification calls for no special discus- 

 sion. The well-(leA-elo])ed basal bed and the 

 numerous lithologic differences which separate 

 it fi-oin unit K have been noted above. The 

 hiclusion of unit K with unit L as part of the 

 ■' Lower Bend," of Mississi])])ian age, as agahist 

 the Pennsylvanian age of the Miirble Falls, is 

 absolutely justified by the fossils. P. V. 

 Rouudy, of the Ihiited States Geological Siu-- 

 vey, who is making very fruitful researches m 

 tlie neglected field of micropaleontology, re- 

 ports that ni the Seaman well the lowest Penn- 

 sylvanian fossils he found were hi the sample 

 from 4,300 to 4,310 feet— that is, about 10 feet 

 above the base of unit J — and the highest Mis- 

 sissiiijiian fossils in the sample from 4,370 to 

 4,:>S0 feet — that is, about 50 feet below the top 

 of unit K. In the Rudd well he found uii- 

 cpiestionable Pennsylvanian fossils in the sam- 

 ])le from 2,920 to 2,930 feet; ])robal)le Pennsyl- 

 vanian fossils hi the sam]>le from 2,945 to 2,950 

 feet, about 12 feet above the contact; ques- 

 tionable Mississi])]nan fossils in the sample from 

 2,965 to 2,970 feet, about 3 feet l)elow the con- 

 ta<t; and definite Mississipjtian fossils in the 

 !?am))le from 2,975 to 2,9S5 feet. 



