178 Rhodora [SEPTEMBER 
lated summits to the highest peaks of the Carolinas. Various minor 
modifications of these ranges might be given, but these are sufficient 
to indicate the general distribution of these plants which in New Eng- 
land, New York, and eastern Canada are confined to granite, gneiss, 
and mica-schist. 
Now, if we examine the lithological character of these areas in 
which Empetrum nigrum, Sibbaldia procumbens, Vaccinium ovalifo- 
lium, and Arenaria groenlandica abound, we shall find that these 
plants are commonly on potassic rocks. Thus, as shown by a geo- 
logical map of Canada, the ancient Archaean area occupies nearly 
the whole district from Labrador to Lake Superior and the Lake of 
the Woods, its western boundary thence swinging northwestward to 
Lake Winnipeg, westward and northward to Lake Athabasca, Great 
Slave Lake, and then north to the Arctic.! This great area is primarily 
of gneiss, granites and mica-schist, rocks, it will be remembered, 
which are markedly potassic; and the area of its great development, 
it will be noted, is strikingly coincident with the general range assigned 
by Professor Macoun to Empetrum nigrum, a plant which in Labrador 
is reported by Low as “abundant throughout the semi-barren and bar- 
ren regions of the peninsula, growing freely on the coast and inland," ? 
and by Delabarre as "the most abundant phenogamous plant of 
Labrador"? Empetrum, it will be remembered, extends along the 
Coast Range from the Arctic to the region of Sitka, and locally south- 
ward. It is also on the mountains of southern British Columbia, 
but absent from the general Rocky Mountain area. When we again 
examine the geological map of Canada, we find that the entire Coast 
Range is designated as “Coast Granite," and that most of the southern 
part of British Columbia (immediately north of Washington) is grani- 
tic. Similarly, in the Rocky Mountains, where Sibbaldia procum- 
bens and some other plants of these potassic rocks occur, the Archaean 
rocks form the “backbone” of the mountains; and in northern Michi- 
gan, where Vaccinium ovalifolium is found, and along the crests of, 
the Alleghanies, where Arenaria groenlandica occurs, we have iso- 
lated southern extensions of the great Archaean axis which is best 
developed from Labrador to Lake Superior and northwestward.‘ 
! The boundaries of this Archaean V-shaped mass are very distinctly shown in Dana's 
Manual, ed. 4, fig. 494. Note there also the isolated areas of Archaean. 
? Low, Geol. Surv. Can., Ann, Rep. n. s., viii. pt. L. 40 (1896). 
3 Delabarre, Bull. Geogr. Soc. Phil. iii. 190 (1902). 
1 See Dana, l. c. 
