ESTABLISHMENT OF A NATIONAL BOTANIC GARDEN. 75 



near its center. This is a poorly drained soil, which would require 

 ditching or tiling for successful use for ordinary farm crops. Over- 

 flows could be prevented only by enlarging the channel or construct- 

 ing levees, or doing both. Some reddish and yellowish sandy allu- 

 vium (18) was mapped along the short streamlets emerging from the 

 uplands in the eastern part of the tract. 



Good agricultural soil is represented in the reddish Wickham 

 gravelly loamy sand (30) and brownish loam (47) occurring on the 

 high bottom or second bottom near the mouth of the principal drain- 

 age way crossing the tract. These soils are successfully used for vege- 

 tables. Corn, oats, grass, and wheat would succeed on them. 



COLLUVIAL FAN SOILS. 



Several small bodies of colluvial material occur along the foot of 

 the uplands bordering the tidal marshes. One small body of reddish 

 loam was mapped in the eastern part of the tract. This represents 

 material that has washed down from the adjacent slopes. A thrifty 

 little grove of young pawpaw was seen on this. 



TIDAL MARSH. 



Three classes of tidal marsh were found as follows: (1) Timbered 

 marsh consisting of bluish to brownish silty material, underlain at 

 about 6 to 15 inches by brown peat (12a) ; (2) timbered marsh con- 

 sisting of reddish and bluish silty clay, with sandy clay in the subsoil 

 in places (12b) ; and (3) open marsh (14) consisting of reddish and 

 bluish silty clay with some sandy clay in the sub soil in places. The 

 timbered marsh is covered with a thick growth of alder, ash, and other 

 small trees, while the open marsh is covered with water lillies, marsh 

 grass, etc. That with peat in the subsoil is very boggy. All this 

 marsh is subject to tidal inundation. The material shows a low con- 

 tent of water-soluble salts and is acid to litmus paper. 



Department of the Interior, 

 United States Geological Survey, 



Washington, May 26, 1917. 

 Col. William W. Harts, U. S. A., 



Secretary Commission of Fine Arts, 



1729 New York Avenue, Washington, D. C. 

 Pear Col. Harts : In compliance with your request of April 26, 

 for a geological survey of the area of the proposed botanic garden, 

 and in acknowledgment of your letter of May 11 : 



There is sent you under separate cover a map showing the prin- 

 cipal features. A cross section shows the underground relations 

 which are relatively uniform under the entire area. The section 

 shows that the beds have a very gentle slope to the east and lie on a 

 floor of granite gneiss which also slopes east. The work was done 

 by N. H. Darton, the geologist who prepared the coastal plain part 

 of the "Washington folio. 



