1914J 
Jackson: Land Vertebrates of Ridgeway Bog 
7 
the apparent conditions of atoll-formation are, (a) a definite maxi- 
mum size and depth of the parent pond; (5) considerable height 
and regularity of the banks of the parent pond; (c) a regular and 
gentle slope of the pond bottom from shore to center; (d) a definite 
original character of littoral vegetation when the pond was at a 
low level ; (e) a reduction within minimum limits of the lateral pres- 
sure and tension of the winter ice; (f) a comparatively prompt 
anchoring of the atoll upon the bottom’’ (MacMillan, 1894, p. 13). 
In another paper MacMillan (1896) has described the vegetation 
of certain bogs near Grand Rapids, Minnesota, and has briefly 
noted the zonal arrangement of the vegetation and the plant 
successions. He found a ^^ring of spruce” between the tamarack 
and the ^^moor,” a condition which I have not observed in northern 
Wisconsin bogs. MacMillan does not discuss the successions 
which follow the tamarack, though mention is made that ^‘com- 
binations of cedar and spruce in the tension line surrounding 
muskeag are met with” (MacMillan, 1896, p. 505). 
Ganong (1897) made a somewhat detailed investigation of sev- 
eral bogs of the “raised” type in New Brunswick. In describing 
the general features of these raised bogs Ganong writes: “These 
are composed of nearly pure Sphagnum, with only traces of other 
mosses, mixed with a few culms of sedges and the slender roots of 
dwarfted woody perrenials. Throughout they are saturated with 
water, which is always cold and clear and free from salts of lime. 
In them there is no decay, and such slight alteration of the plant 
substance that from top to bottom they consist of compacted 
moss, slightly altered chemically, forming a very spongy peat, and 
never, except at the very bottom, the compact peat of flat bogs. 
Their surfaces are without large vegetation and bear but a scanty 
growth of dwarfted shrubs and trees and a few herbs, all of the 
northern aspect. The surfaces are always raised to a convex 
form, and the slopes are often abrupt” (l.c., p. 132). In the 
raised parts of these bogs Ganong found dwarfted tamarack and 
spruce trees up to a height of one foot; a spruce seven inches tall 
had twenty-eight rings; shrubs, such as ‘‘Cassandra calijculata, 
Kalmia glauca and Vaccinium canadense” “rarely exceed six and 
never eight inches in height” (l.c., p. 136). He did not find a 
definite zonal arrangement of the vegetation in these bogs. “Ani- 
mal life is very rare on the bogs, and seems to be confined to a 
