TERRACE SECTIONS 145 



21. Granite gravel pit. — This is a railway pit located at the edge of 

 the Granite terrace on the north and east side of Bloody Run, about a 

 mile west of Granite. Near the south end it presents the following sec- 

 tion : 



A gravelly yellowish stratum of uncertain age, 3 to 6 feet. 



Bed of sand and gravel, 3 to 5 feet. 



Weathered grayish drift, probably Kansan, 5 feet exposed. 



A worn fragment of the molar of a horse was found in the gravel bed. 



This is just opposite that part of the terrace which Wilder represented 

 as a portion of the Altamont moraine, and probably has the same struc- 

 ture, being cut off only by the narrow valley formed by Bloody Run. 



The valley of Bloody Run east of Granite contains beds and banks of 

 gravel which may be more recent. There are numerous evidences of 

 water action at and east of Granite and in the first railway cut west. 

 The immediate valley of the creek is very narrow just west of Granite, 

 and the peculiar topography, together with the presence of stratified 

 beds at and east of Granite, might suggest a damming of the creek at a 

 point just west of Granite. 



The valley of this and other tributaries of the Big Sioux River should 

 be studied more fully. 



Satisfactory sections were not found on the terraces above the Iowa 

 State line. The great terrace west of Brandon is largely made up, at 

 least in its western part, of gravel, but along the wagon road it also shows 

 a silt overlain by 4 to 6 feet of loess-like material. The latter does not 

 occur excepting where there is underlying silt and it blends with it more 

 or less. 



The gravel pit on the south side of the terrace island at Sioux Falls 

 shows cross-bedded sand and gravel, with a thin covering of a yellow 

 sandy material, which is probably in part aeolian. 



PLEISTOCENE FORMATIONS 



The Pleistocene formations as exhibited in our territory are here dis- 

 cussed somewhat more in detail. 



Nehraskan drift. — As noted in the several sections, the Nebraskan drift 

 is exposed at numerous points on l)oth sides of the Big Sioux River in 

 both Iowa and South Dakota. 



It most frequently appears in the form of a ])lue-l)lack, very tough, 

 impervious joint-clay containing scattered boulders and pebbles and 

 usually breaking up on drying into very small "joint" fragments. Some- 

 times it contains ferruginous bands and streaks, and the uppermost por- 



