60 
certain extent at a place called Round Lake, about 20 miles north of 
Peace point, in the summer of 1928. Characteristic species are Potentilla 
Anserina, Sisyrinchium angustifolium, Oxytropis splendens, Potentilla nor- 
vegica var. hirsuta, Agrostis scabra, Arenaria dawsonensis, Anemone cana- 
densis, Thalictrum venulosum, Agropyron trachycaulum var. typicum, and 
Equisetum prealtum. In many of its elements this association resembles 
the prairies above described. 
The lower levels have a somewhat different type of vegetation whose 
primary species are Carex rostrata and Calamagrostis inexpansa var. 
brevior. The prairie aspect is maintained, but the substratum is more 
moist and bears a rich growth of the above species. Notable associates of 
these are Phalaris arundinacea and Gentiana elegans. If this area were 
drained more completely it would probably acquire a vegetation similar 
to that of the higher levels. 
The wet margins of the small stream have an association of Carex 
rostrata, Equisetum limosum, Eleocharis acicularis, E. palustris, and 
J uncus nodosus. Accompanying species include Shim suave and Glyceria 
borealis . In the quieter pools are Potamogeton Richardsonii, Polygonum 
natans forma Hartwrightii, Sparganium sp., and Equisetum limosum. 
Where the water collects in larger pools there is a more extensive association 
of aquatic species, with Potamogeton Richardsonii most abundant. Other 
species found there are Potamogeton foliosus, Callitriche hermaphroditica , 
Sagittaria cuneata, Alopecurus aequalis, and various algae. Alopecurus 
grows in the shallow water or very wet sand at the margin of the pond, as 
does also Sagittaria. Dry stream and pool bottoms such as occur in other 
parts of the depression have a semi-prairie vegetation like their sur- 
roundings. 
The transition from the sink-hole vegetation to the adjacent timber 
is a sharp one. A small, shrubby growth of Rosa acicularis, Symphori- 
carpos occidentalis, and other shrubs of the upland woods marks the border. 
SUMMARY OF PRAIRIE VEGETATION 1 
The foregoing discussion shows two major types of prairie-opening 
vegetation, the distribution of which seems to be directly correlated with 
the water-holding capacity of the soils. They are largely confined to 
regions in which the soil has a considerable percentage of clayey materials, 
and in which the post-Glacial lakes had their settling basins. Heavier soils 
have a turf dominated by blue- joint grass Calamagrostis canadensis var. 
robusta, the sedge Carex trichocarpa var. aristata, blue grass Poa pratensis , 
or combinations of these with a variety of other perennial herbs. Lighter 
soils are dominated by more xerophytic grasses and sedges, of which Agro- 
pyron trachycaulum var. unilaterale, Stipa comata , Carex siccata or C. 
obtusata, Koeleria cristata, are the most abundant. The commonest varia- 
tion from these types is caused by local salt deposits from brine springs, 
which introduce a halophytic element. 
As there is no evidence of an earlier, forested condition, the grasslands 
or possibly tundra forebears of them must have persisted as a type of 
1 A more complete summary of the problem of the northern prairies will be found in 
the author's discussion of the Peace River grasslands (55). 
