1898] VEGETATION REGIONS OF THE PRAIRIE PROVINCE 393 
formation of buttes and hills, (3) the grass formation of high 
prairies and sandy plains. The undershrub formation is not 
peculiar to the foothills of the prairie province ; it here covers 
but a small area in comparison with the vast stretches occupied 
by itin the Great Basin province. In the foothills, this forma- 
tion exhibits two types, the one confined to high, somewhat 
grassy table lands, the other found solely on alkaline lands, or 
bad lands. The former may be termed the sagebrush type, the 
latter the greasewood-white-sage type. The facies of the sage- 
brush formation are Artemisia tridentata, A. frigida, A. filifolia, A. 
canadensis, and A. cana, Chondrophora Howardit, C. nauseosa, and 
—C. Douglasii, and Gutierrezia Sarothra. The grasses are species 
of Bouteloua, Agropyron, and Koeleria cristata. The facies of the 
greasewood-white-sage formation are Sarcobatus vermiculatus, 
Ewrotia lanata and Atriplex confertifolia. Grasses are practically 
, absent. Other secondary species are few.  Ptiloria tenuifolia, 
Aster multiflorus, Cryptanthe Fendleri, and Chrysopsis villosa are the 
Most important. 
Inthe foothills of the central portion of the prairie pro- 
vince, the mat and rosette formations are the most widely dis- 
tributed. Mats and rosettes have almost exclusive control of 
buttes, cliffs, rocky ridges, and sandy hillsides. Two types may 
be distinguished, the mat formation of buttes and cliffs, and the 
_ -Tsette formation of sandy hillsides. No well-marked group 
Of facies is regularly present. The ground-tone of the rast 
formation is derived from a large number of mat-forming species, 
— Arenaria Hookeri, Gilia spicata, Orophaca caespitosa, Eriogonum 
comawum, E. flavum, Gilia iberidifolia, Pllox Hoodii, and Homaletis 
_*Montanus, The secondary species are for the most part invaders 
‘tom the sand hills, such as Mertolix serrulata, Malvastrum coc 
— ineum, Rumex venosus, Psoralea lanceolata, Aristida purpurea, 
sillenberg 1a pungens, etc. The rosette formation peg 
_ “tacter from Polygala alba, Paronychia James, Pentstemon 6s 
: ang faeruleus, Phlox Douglasi, and Oreocarya coun "and ae 
ation is, in reality, transitional between the mat a 
_ 888s formations of the foothills, and its secondary species ar© 
_tived chiefly from them. 
