366 BOTANICAL GAZETTE [NOVEMBER 



able extent are occasionally met with. In the region of the great 

 plains they are sometimes found beneath a surface covering of sand 

 and wind-blown deposits. TODD (54, p. 121) has mentioned the 

 occurrence of such peat deposits in eastern South Dakota. BARBOUR 

 also reports such deposits from central and eastern Nebraska (2). 

 On the basis of their field relations and certain fossils which they 

 contain, they are believed to be of Glacial and early Pleistocene age. 

 If the plant materials of these deposits could be carefully worked 

 over with reference to their successive floras, we might hope for some 

 new light on glacial climate, since a part of the deposits are beyond 

 the margin of the Wisconsin ice sheet. But even their location and 

 existence give evidence of climatic change, and plant and animal 

 migration. Although now widely separated from the region of 

 active bog formation, they are historically connected with this division. 



Among the mountains of both the eastern and western United 

 States, bogs and swamps are to be found in association with mountain 

 lakes. More frequently than otherwise these depressions are con- 

 nected with former local glaciation, perhaps the most frequent 

 situations being those afforded by the damming back of water by 

 terminal and lateral moraines. Basins for peat accumulation are 

 also found in solid rock made by glacial erosion. The conditions 

 here are quite similar to those of the north, the altitude bringing 

 about the same general effect as the latitude. The analogy is still 

 further shown on mountains in moist regions where alpine meadows 

 are strongly developed. Not only are the plants related to those 

 of the tundra, but the deposition of peat or humus is again irrespective 

 of basins. 



In many places east of the great plains there is another type of 

 situation not directly connected with glaciation, but in which vegetable 

 debris may accumulate to considerable thickness, viz., about the 

 debouchure of cold springs. Toward the north these springs may 

 bring about humus accumulation on slopes, but further south peat 

 is usually associated with pools and small lakes. 



The second group of situations in which peat accumulation takes 

 place on a grand scale, are those associated with coastal plain phe- 

 nomena, such as the rising and sinking of the land, the irregular 

 deposition of alluvial materials in deltas, and the extension of the 



