696 J. L. TILTOX STRATA NEAR STUART, IOWA 



seam of coal specially designated in the cross-sections that is mined to 

 the west, along Deer Creek, and formerly at Eureka mine, to the south- 

 west.) Xext come 14 inches of a brownish micaceous sandstone above 6 

 feet of arenaceous shale; then 3 feet of a dark arenaceous limestone lying 

 10 feet above the river bed at that point. 



Interest centers in the 3 feet 10 inches of limestone (number 1 of the 

 above section), Bain's "fragmental limestone." Below this bed of lime- 

 stone the strata are distinctly Des Moines in character, and were so con- 

 sidered by Bain when he mapped Guthrie County. The bed of frag- 

 mental limestone (number 1) was, however, considered the base of the 

 Missouri stage, and the limestone beds up the hill (which are thicker as 

 exposed farther west) were considered Bethany Falls 4 (Earlham) and 

 Winterset beds respectively. The beds can be traced through sections 7, 

 8, 9, 17, 18 (range 30), and sections 12 and 17 (range 31) north of the 

 creek, and sections 21, 20, 19 (range 30), and section 14 (range 31) 

 south of the creek. 



A detailed comparison between the beds of limestone (number 1) that 

 is fragmental in character (previously supposed Hertha) and the true 

 Hertha east and south of Earlham — and elsewhere south, even into Mis- 

 souri — reveals marked differences : This Guthrie County limestone north 

 of Stuart is in one continuous bed, while the real Hertha elsewhere is in 

 two portions, with a bed of shale between them. Furthermore, this Guthrie 

 County bed of limestone is of a very different texture than the Hertha. 

 It is brownish and arenaceous, the fragments not composed of calcareous 

 ball and rod-like lumps found in the Hertha. They are arenaceous. 

 Along with Composita subtilita the present writer found an imperfect 

 shell that he judged to be Marginifera muricata, the index fossil of the 

 Des Moines stage. The fauna listed on page 448 of the Guthrie County 

 report 5 is not found in the Hertha limestone of Iowa as characteristic of 

 it, even though a tabular list of fossils of all kinds found over large areas 

 may include them all. 



The brownish weathered sandstone about 15 inches thick (number 3) 

 is not in the least like the foot and 10 inches of dark blue limestone found 

 at Winterset, in the upper portion of the Ladore shale, above the Hertha 

 limestone, with which it should agree if Bain's correlation were correct. 



The next limestone (number 5), which is 5 feet thick and located 

 above 4 feet of shale, has a character in a general way like that of the 

 Bethany Falls (Earlham) limestone, but the lower beds lack the thick- 



4 John L. Tilton : The proper use of the geological name "Bethany." Proceedings of 

 the Iowa Academy of Science, 1913. 



5 Iowa Geological Survey, vol. vii, p. 448. 



