1905] T RAN SEAU 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: 

 (i) 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 

 by a 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 

 recessional 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 

 than depressions containing water. When the tundra or "barren 

 ground" is reached, the accumulation of humus is almost universal. 

 The contrast with our own region is well brought out in RUSSELL'S 

 account of the tundra (43, p. 129). The vegetation 



grows rapidly during the long, hot, summer days, dies below and partially decays, 

 but becomes frozen and has its complete destruction arrested, while the dense 

 mat of roots and stems continues to thrive. In this way an accumulation of 

 partially decayed vegetable matter is formed, which increases in thickness from 

 year to year by additions to its surface. The process is similar to that by which 

 peat bogs are formed in temperate latitudes, except that the partially decom- 

 posed vegetation becomes solidly frozen. It is in reality an example of cold 

 storage on a grand scale. 



Under existing climatic conditions there does not seem to be any limit to the 

 depth such deposits may attain. The amount of carbonaceous material already 

 accumulated in the tundras of America and Asia must equal that of the most 

 extensive coal field known. 



South of the boundary above described, peat deposits of consider- 



