195] TRANSEAU—BOGS OF THE HURON RIVER VALLEY 365 
THE GEOGRAPHIC DISTRIBUTION OF PEAT DEPOSITS. 
In North America the distribution of recent peat deposits may be 
conveniently summarized under two heads, genetically unrelated: 
(1) those of glaciated regions; (2) those of the coastal plain. 
The peat of the glaciated area constitutes the great bulk of these 
American deposits. The southern boundary of this region is marked 
bya line passing westward from central New Jersey through northern 
Pennsylvania and Ohio, central Indiana and Illinois, thence north- 
ward through southern Wisconsin, northwestward to the Minnesota 
valley and the Red River of the North in Manitoba, westward through 
northern Assiniboia and southern Alberta to the Rockies. Here 
the boundary is deflected southward into Montana, but in crossing 
toward the coast it is again carried northward into British Columbia, 
and finally southward among the Cascades of Washington to the 
Pacific Ocean. 
Along. this southern border the peat deposits are exceedingly 
scattered and make up a small fraction of the total land surface. 
They have accumulated under water in depressions among the 
Tecessional moraines. As we go northward, the relative proportion of 
Peat bogs and peat deposits regularly increases, and there is a notable 
tendency toward the accumulation of pure humus in situations other 
depressions containing water. When the tundra or “barren 
stound” is reached, the accumulation of humus is almost universal. 
The contrast with our own region is well brought out in RUSSELL’S 
‘ccount of the tundra (43, p. 129). The vegetation 
sews rapidly during the long, hot, summer days, dies below and partially nop 
pom frozen and has its complete destruction arrested, while —<. ie 
Partially 4 and stems continues to thrive. In this way an ae sie 
Year AS aelag vegetable matter is formed, which ——— in dit be whic 
; y additions to its surface. The process 1s similar por LF aie 
fied ar. formed in temperate latitudes, except that the pa ole of cold 
Sorage _ becomes solidly frozen. It is in reality an exam 
a grand scale. é 
Under existing climatic conditions there does not seem to be any limit 
oo" may. attain. The amount of carbo ei 
extensive ig the tundras of America and Asia must equa 
eld known. 
South of the boundary above described, peat deposits of consider- 
