1905] TRANSEAU—BOGS OF THE HURON RIVER VALLEY 363 
but the blue-green algae may be present up to the water’s edge, in 
such situations frequently forming marl pebbles. The lower limit 
of existence is largely determined by the transparency of the water, 
and may lie between 20 and 30 feet (6-9™). Of the littoral plant 
associations there are commonly two quite distinct divisions, the 
outer made up largely of submerged or floating pondweeds and water- 
lilies, the inner of half-submerged rushes and sedges. Both are con- 
ceed in the process of peat formation. Under such conditions 
there naturally develop, in regions of calcareous underground waters, 
an outer zone of chara dominance and marl deposition, and an inner 
zone of pondweed-sedge dominance and peat deposition. Varia- 
tions in the slope of the bottom, in the amount of wave action, in the 
presence of shore currents, and in the color of the water, determine 
whether one or both of these processes shall go on, and to what 
extent these activities are kept distinct or grade into one another. 
In the case of the peat, however, the process is not dependent 
upon water species alone. They act. merely as forerunners of a 
denser and more luxuriant vegetation which frequently is of greater 
quantitative importance. Briefly, we may note here that in the case 
of the bogs, unlike that of the swamps, the plants which develop on 
the margin, especially Carex filiformis and forms of Eriophorum, 
are able to secure all of their food materials from the water and air 
and build their own substratum. ‘This tangle of roots and rhizomes 
usually attains a thickness of several inches, and on account of its 
— gravity floats on the surface of the water. Upas this 
tion the sphagnum and bog shrubs advance, adding their 
ae to the débris. Later, these are followed by such tree forms as 
5 Sian Coincident with this increased weight at bby ae 
2 ediaeatai comes the progressive submergence © ine? er 
, and its gradual disintegration and humification. e 
Pentying fig. 4 will serve to illustrate this process. 
— the last two years much has been promised segues _ 
Danish . of the peat deposits in this region for fuel purposes. sped 
drying . a been organized, and the machinery necessary aM 
Ca nd consolidating of the peat has been much Improve" 
Pac and Chelsea, factories have been erected, and attempts are 
M8 Made to place the industry on an economic basis. If these 
