ALTAMONT MORAtNE 15 1 



That part represented by Wilder as located in Lyon County, Iowa, con- 

 sists cither of terrace gravels or of ridges which are a part of the Kansan 

 uplands on this side of the river, and differ in no important particular 

 from corresponding formations in other parts of this region. 



The ridge beginning west of Granite and extending northward toward 

 Sioux Falls likewise shows only Kansan or loess at the surface, and this 

 also is evidently related to the uplands on the Iowa side. 



The conclusion naturally follows that the elevations heretofore specific- 

 ally referred to the Altamont moraine are Kansan and belong with the 

 Kansan area on the Iowa side. 



The gravels of the river terraces. — The sands and gravels in the ter- 

 races along the Big Sioux Eiver have been regarded as Wisconsin gravel 

 trains. 



The writer at first inclined to the opinion that they were Aftonian, but 

 has come to the conclusion that they are Kansan. In at least one section, 

 number 21, the bed of gravel rests on what appears to be Kansan drift, 

 though the terrace sections in the vicinity of Granite show much irregu- 

 larity in the arrangement of strata, and it is difficult to determine how 

 much shifting and mixing has taken place. It is also noteworthy that 

 these sands and gravels are not clean like most of the Aftonian, and no 

 fossils have been found in them excepting the worn fragment of the molar 

 of Equus in section 21, but this was probably derived from older strata, 

 and, moreover, it was associated with a bone of much more modern 

 appearance. 



Perhaps the most satisfactory evidence that these gravels are Kansan is 

 furnished in the vicinity of Sioux Falls. The high ridges and knobs 

 lying to the northeast of Sioux Falls consist in large part of sand and 

 gravel. The gravel in some cases forms the uppermost portions of the 

 mounds or ridges, which are then covered by a very scant, stunted vegeta- 

 tion. 



It is evident that these gravels are not older than the Kansan, for at a 

 number of points typical Kansan may be clearly seen below them. That 

 the gravels do not belong to a later drift, but are closely connected with 

 the Kansan, is shown by the fact that at several points loess appears 

 above them, and on at least one of these ridges two loesses, the lower gray 

 and the upper yellow, overlie the drift and gravels. As previously noted, 

 the gray loess always closely follows the Kansan drift and associated for- 

 mations, and its presence here, capping a ridge more than 200 feet above 

 the river, shows that the underlying materials are not younger than the 

 Kansan. 



Another fact is worthy of note : As has been pointed out, there are no 



