PLANT LIFE IN OKLAHOMA. 39 



beneath the floor of the plain. At this period the surface becomes white 

 with an incrustation of salt. In most of the other salt plains the salt 

 springs are flowing onto the surface, and the evaporation results in a 

 crust of salt sometimes several inches thick on parts of the floor, of the 

 plain. One of these, in the valley of the Cimarron Kiver, known 

 as the Big Salt Plain of the Cimarron, beginning about 10 miles 

 south of the Kansas line and extending about 8 miles down the river, ia 

 "the only place where rock salt can be obtained on the surface in all the 

 plains country. This salt was known and used by the Indians, and was 

 an article of trade from the Gulf to the British line, and this locality was 

 a well-known geographical point from which distances were reckoned."* 

 On several of the others salt is abundant and has been manufactured for 

 local market at three or four of them. 



The most conspicuous biological feature of the Salt Plains is the 

 almost complete absence of life either in the water or soil. In some of 

 the less concentrated ponds ditch grass {Ruppia maritima) is found. 

 About their margins are found cat-tail {Typha angu^tifolia) , bug-seed 

 (Corispermunt hyssopifolium) , tumble-weed (Cydoloma antriplicifol- 

 ium), sea-blite (Suaeda linearis), and water rush {Scirpus campestris 

 var. pludosus) ; while sea purslane {Sesuvium, sesUe) grows in the salty 

 sand of the floor plains. Salt grass, {Disticlilis spicata), water-rush 

 (Ssirpiis Torrey), xush grass {Sporobolus airoides), and sand rache 

 (Atriplex argentea) are found about the margins, but are occasion- 

 ally likewise in other less alkaline parts of the State. Salt-marsh fleabane 

 (Pluchea camphorata) is occasionally found in slightly alkaline situa- 

 tions about the plains and is not reported elsewhere in the State. 



The size of the Great Salt Plain, about 12 miles long and 6 miles 

 across in the broadest place, and its low position within a rather extended 

 basin, lead to the belief that it is the site of an ancient lake which is 

 called Lake Barde. The presence of the Least Tern nesting regularly 

 in considerable numbers upon this plain and the Big and Little Salt 

 plaias of the Cimarron is taken by ornithologists as evidence of a former 

 ialand sea in the vicinity. This is a sea coast bird found rarely else- 

 where except on the Florida, Gulf, and Lower California coasts. 



GYPSUM HILLS. 



Two formations of gypsum occur in the western part of the State 

 (PL XI). These are exposed along the juncture of valleys and higher 

 tracts, and mostly have the form of bluffs and buttes, the latter frequently' 

 called G-lass Mountains or Gloss Mountains. The gypsum caps, on the' 

 blufis or butts preserve the top of the elevation, with their slow decay- 

 ing rock, while the underlying red clay is eroded more rapidly, often 

 leaving perpendicular faces. (See Plate XX.) The rapid erosion of 

 the sides of these hills and the excess of calcium sulphate (gypsum) 

 on their tops make unfavorable conditions for plants. A few species are 



*Okla. Geol. Survey Bull. No. 11, p. 205. 



