LITHOLOGIC CORRELATION IN BEND SERIES, TEXAS. 



13 



in smaller amount between 4,040 and 4,050 feet. 

 The lower sandstone was chosen to mark the 

 boundary between units H and I in tliis well 

 because it is probably the lowest occurrence of 

 such material, because of its greater abun- 

 dance, and because it seems to be more closely 

 related to the more definite lower boundary of 

 unit H in the deeper-water deposits of the Rudd 

 well. A light-colored sandstone shown just 

 above 2,765 feet in the Rudd well and indi- 

 cated by mere traces in the sample may be the 

 equivalent of the one between 4,040 and 4,050 

 feet in the Seaman well. 



A peculiarity of the basal sandstone of unit 

 H in the Seaman well is its shattered condition. 

 Delicate veinlets filled partly vrith calcite and 

 partly mth fibrous chert cut thi-ough sand 

 grains, tlu-ough sulphide concretions, and 

 through cement. 



In both wells an mcrease of lime in the upper 

 part of unit H is shown, reaching its maximum 

 just below the base of unit G. 



UNIT J. 



Unit J falls in both wells into two parts 

 which are very similar but are separated by a 

 pronounced maximum of clay sharply bounded 

 against the upper part. This maximum is ac- 

 companied in the Seaman well by a slight sandi- 

 ness and especially by a peculiar hard, dense 

 black calcareous material containing a little un- 

 usually fresh, rather coarse glauconite and a few 

 phosphate spherules — material of the same 

 type as that which marks the base of the unit. 

 In the Rudd well the clixy maximum is accom- 

 panied by a relatively large amount of coarse 

 sandstone and sand. As the two parts are in 

 general very similar and as vertical limits of 

 the occurrence of the basal type of materials 

 have not been determined and therefore the 

 boundary can not be definitely placed, the two 

 parts have not been separated as distinct units. 



A peculiar feature of the lower division is that 

 it is decidedly more sandy in the Rudd well 

 than in the Seaman well. The difl^erence does 

 not seem to be an error of observation, as sam- 

 ples from the upper part of the lower division 

 in the Seaman well were reexamined and no 

 sand or sandstone fragments were found, 

 though in the Rudd well most of the sand rep- 

 resented in the lower division occurs as sand 

 or sandstone easily recognized in the sample. 

 This relation of the lower part of unit J in the 

 32333°— 22 2 



two wells is dii'ectly contrary to that prevailing 

 in all the units previously discussed and is 

 considered further on page 17. 



The base of unit J in both wells is marked by 

 probably the best-developed glauconite bed 

 encountered in the section so far discussed — 

 that is to say, the glauconite is imusually 

 abundant, coarse, fresh looking, and thickly 

 scattered tlu'ough the thm sections. In the 

 material from the Rudd well some of the glau- 

 conite partly replaces or fills calcareous skele- 

 tons of organisms. There are an unusually 

 large number of phosphate nodules. Sulpliide 

 is abundant. vSand is rather abundant in the 

 material from the Seaman well but scarce in 

 that from the Rudd well and not coarse in 

 either. Shells and fragments of shells occur 

 in both wells but are particularly abundant in 

 the Rudd well. In many of the fragments ex- 

 amined these materials lie in a peculiar dense 

 to opaque bro\\^l matrix different from any 

 shales in the section. Many chips of this mate- 

 rial in the solid look like limestone. A similar 

 substance forms the body of several chips 

 obtained near the middle of unit J, especially 

 in the Rudd well, and is the matrix of the 

 glauconite noted in the sample from 4,230 to 

 4,240 feet in the Seaman well. Possibly this is 

 phosphatic material. It requires further study. 



A peculiarity of the glauconitic bed in the 

 Seaman well is its occurrence in the sample from 

 4,300 to 4,310 feet but not in that from 4,310 

 to 4,320 feet, though the character of the mate- 

 rial from the lower interval leaves little doubt 

 that it belongs to unit J and not to imit K. 

 .A.S indicated in the introduction (p. 3), in.any 

 glauconite layers such as are characteristic of 

 unconformities are not directly at the contact, 

 but here the distance separating them is 

 unusually great. In the Rudd well, on the 

 contrary, the glauconite is evidently very near 

 the contact. 



UNITS K AND L. 



In the percentage logs units K and L respec- 

 tively appear very similar in both wells, unit K 

 being calcareous and separated rather sharply 

 from unit L. The beds of both units show 

 several lithologic characteristics that distin- 

 guish them from overlying beds. 



In the Searfian well unit K consists of lime- 

 stones of a distinct blue-gray color in the solid, 

 as against the black-gray of the overlying lime- 



