24 FIELD OPERATIONS OF THE BUEEAU OF SOILS, 1^19. 



intermittent streams and surface wash and deposited upon the valley 

 slopes of the larger streams. Wind has also played an important 

 part in their formation. The topography varies from gently un- 

 dulating to rolling. Drainage is everywhere good. The Bridgeport 

 soils differ from those of the Valentine series, which they often re- 

 semble, in the calcareous nature of their lower subsoils and of gravel, 

 which is generally scattered in small quantities over the surface. 



The Mitchell series includes light-brown or buff-colored silty soils, 

 which in this countj'^ cover terrace-like benches and evenly graded 

 slopes. They are composed mainly of colluvial and wind-blown 

 materials, derived principally from the Brule clay and to a lesser ex- 

 tent from the Arikaree and Gering formations. These soils have 

 been transported only short distances and differ but slightly from the 

 soils of the Epping series. The Brule clay formation underlies them 

 at depths ranging from 3 to 40 feet. The topography varies from 

 level to gently rolling, but the drainage is usually good. 



The surface soils of the types comprised in the Tripp series are 

 grayish-brown to brown. The subsoils are light brown to gray and 

 highly calcareous; in places the lower subsoil is almost white. The 

 Tripp soils are alluvial, being developed on both high and low ter- 

 races along Pumpkin Creek and its tributaries. They consist of 

 sediments brought down from exposures of the White Eiver and 

 Loup Forks Beds, with which sediments there has subsequently been 

 mixed a large proportion of wind-blown material in places. The sur- 

 face drainage over most of the series is not well established, but the 

 porous subsoil carries off all the surplus water. The topography is 

 almost flat to very gently undulating. 



The types of the Cheyenne series have brown surface soils and 

 grayish-brown, porous, gravelly subsoils, generally calcareous. The 

 Chejenne soils are derived from alluvial terrace materials and from 

 colluvial wash which has partly filled the higher valleys and draws. 

 They differ from the Bridgeport series in the large amount of gravel 

 in the subsoil. The soils lie high above overflow and are well drained, 

 often being droughty. 



The types of the Laurel series have light-brown to gray soils 

 underlain by light-gray subsoils. Both soil and subsoil are highly 

 calcareous. Iron stains are common below 15 inches. There is often 

 a porous stratum of sand and gravel in the lower subsoil. The 

 Laurel soils occupy first bottoms, and are composed of sediments 

 derived from the White River and Loup Fork beds, recently de- 

 posited along the stream channels. The surface is flat and drainage 

 is generally poor. The soils are subject to overflow at varying 

 intervals. 



The types in the Scott series are dark brown to almost black in the 

 surface soil, which is underlain at about 10 inches bv a heavy, com- 



