80 THE NAUTILUS. 



Moreau and Grand rivers. A very small portion in the north- 

 western part is drained by the Little Missouri River which flows 

 north into the Missouri. 



There are no lakes or ponds in the western half of the State, 

 and the small creeks are dry most of the year. There are num- 

 ber of small lakes and ponds in the eastern part, formed by the 

 glacier scooping out depressions and damming up small valleys. 



The lakes, ponds and rivers east of the Missouri River abound 

 with shell-life characteristic of the northern region. Owing to 

 the velocity of the current and the rapid deposition of sediment, 

 no shell-life exists in the Missouri River. For the same reason, 

 and the presence of alkaline substances, the same is true of 

 most of the rivers flowing into it from the west. In the north 

 fork of the Grand River, well up toward the head in Perkins 

 County and in the " Ft. Benton loam ", I found Anodonta gran- 

 dis and Sphserium. striatinum var. acuminatum. Just east of the 

 Black Hills, in Washabaugh County, in the Yellow Medicine 

 Creek, I collected Anodontoides ferussacianus and Sphserium sul- 

 catum. I think that the former may be found in several creeks 

 in the Pine Ridge Reservation where the creek-bed is still in the 

 "Pine Ridge loam". In fact they were reported from two 

 other creeks by Indians whom I talked with last August, and 

 who said they "had roasted and eaten 'em". I have found 

 several species of very old ' * recent ' ' clam shells along terraces 

 of the first floodplain of a number of these " badland " creeks 

 and rivers, which proves that, before the streams eroded down 

 into the Tertiary or Cretaceous clays, they were inhabited by 

 mussels. 



The Black Hills, in the southwestern part of the State, is a 

 dome-shaped mountain 100 miles long and 50 wide, from 5000 

 to 7200 feet above sea level. The higher elevations are covered 

 with pine timber and lower down along the spring-fed creeks 

 are deciduous trees and thickets. The rainfall is one-third more 

 than on the surrounding plains. There are no lakes, and most 

 of the streams are not congenial for shell-life on account of the 

 extremely rapid current. From a collector's standpoint the 

 Black Hills were a disappointment to me. Perhaps I expected 

 too much. But there is a field for more work and especially 



