BLUFF SECTIONS 143 



Bluish joint clay, capped with soil, evidently Kansan, 6 feet. 

 Sand and gravel : 



Gravel, 6 feet. 



Sandy silt, 3 to 5 feet. 



Cross-bedded sand and fine gravel, 4 to 5 feet exposed. 



Fragments of a shell, probably Unio, and a valve of Spha>rium sulca- 

 tum were obtained from the lower sand. Mr. Collins also found a molar 

 of Equus scotti and a molar of Castoroides in the lower sand and gravel 

 of this pit. 



The top of the gravel in this pit is about on a level with the top of the 

 fossiliferous silt layer in the second Illinois Central cut. 



Other pits in the vicinity show cross-bedded sand and gravel. 



16. Rpad-cut in section 14, township 101 north, range JfO west. — This 

 cut is just east of the Illinois Central Railway. It is of interest because 

 it further illustrates the irregularity of the strata of this region. On the 

 south side of the wagon road a large sand boulder is included in blue 

 joint clay, which is evidently Kansan drift, and on the north side Kansan 

 drift and sand and gravel are irregularly folded. 



Other sections in the vicinity still further emphasize this irregularity. 

 The road-cut just east of section 15 shows an irregular interstratification 

 of Kansan drift, sand, silt, gravel, and boulders, and only a few rods east 

 of that, on the north side of the road, a well-boring near Mr. Danbury's 

 house showed about 10 feet of drift ( ?) and then about 75 feet of fine 

 sand. It is difficult to find two sections in this immediate vicinity which 

 present the same materials arranged in the same relation to each other. 



The sections on the north side of the river in Sioux Falls almost uni- 

 formly show Kansan drift overlain with a stratum of sandy silt or, more 

 rarely, sand and gravel. A typical section is illustrated in plate. 10, fig- 

 ure 2. This section is located on the east side of Dakota Avenue, south of 

 Russell Street, and presents the following members : 



c. Yellow (or nearly black) silt, or in part seolian, 1 to 1.5 feet. 

 h. Gray, sandy silt, laminated, with occasional bands of sand or fine 



gravel, 1.5 to 2 feet. 

 a. Kansan drift, 5 feet exposed. 



Occasionally in these sections irregular layers of sand and gravel occur 

 in the drift, as on the east side of McClellan Street opposite Main Ave- 

 nue, and at several points a dark-gray silt, similar to the fossiliferous silt 

 in section 13, is irregularly disposed in the Kansan drift. The lower part 

 of the McClellan Street cut shows such a mass (containing some pebbles 



