1897.] Peculiar Zonal Formations of the Great Plains. 969 
the straw-colored Stipa, give a dark green tone to the forma- 
tion. The floral covering, composed of the Stipa and the pep- 
pergrass-cactus formations, is seamed here and there with old, 
abandoned trails, and what may by courtesy be called roads. 
These have necessarily originated extremely narrow, but often 
very long, minor tensions between the original floral covering 
and the invading roadside flora. Along the roads travelled at 
present, these tensions have attained expression in a narrow 
zone at either side. In some instances, this zone consists of 
dwarf individuals of Helianthus petiolaris, in others of Malvas- 
trum coccineum, or of Gutierrezia sarothræ, in still others, of 
dwarfed plants of Salsola tragus, closely appressed, but conspic- 
uous on account of the unusual deep green color. Not infre- 
quently, Malvastrum and Salsola intermingle to constitute the 
zone. A common result of such a tension in the Stipa forma- 
tion is to accentuate the size, and density of growth of the 
Stipa to such a degree that the formation is bordered along the 
road by a most conspicuous zone composed wholly of its own 
facies. In the same formation, the Stipa zone is sometimes 
suppressed, and its place is occupied in part by scattering, 
silver-purple bunches of Artemisia frigida. In trails a long 
time abandoned, the sterile strip between the bordering zones 
disappears, being encroached upon and vanquished by the 
plant constituting these zones. Such trails then become not 
only striking members of the floral covering, but not altogether 
- canny features of the landscape as well. From the base of 
Scott’s Bluff, a deeply sunken trail extends far toward the Wild 
Cat mountains in the southeast, marked over sun-browned 
plain and ridge by an endless band of dark green, due to the 
dense bunches of Gutierrezia: sarothre. The stage-road from 
Harrisburg over the hills and undulating plains of Kimball 
county is flanked on either side by a trail, once well-worn, but 
now densely crowded with the silver-purple tufts of Artemisia 
frigida. These floral land-marks run parallel to the stage route 
for perhaps a half-score of kilometers, then swinging abruptly 
to the southwest, they pass on over valley and ridge, disappear- 
ing in the one only to reappear upon the ri until the we 
refuses to follow further. 
