36 Smithsonian Exploration in Alaska in 1904 



A brief sketch of some of the conditions of plant hfe in 

 Arctic lands will further make this clear, and at the same time bring 

 out a number of facts which have an important bearing on the 

 question of plants and climatic conditions," etc. 



X. The Land Ice of Arctic and Sub-Arctic Regions 



Ice deposits may be classified under five heads in chronological 

 sequence as follows : 



I. glacial ice of snow origin 



Glacial ice does not enter into this discussion beyond what has 

 been already said ; that its erosive action in the higher lands pro- 

 duced most of the immense quantity of detritus which forms the 

 deposits of the Pleistocene period, and the waters from the melting 

 snow and ice supplied the great volumes necessary to transport this 

 material over the wide areas it now occupies. The ice in this case 

 is of snow origin and its formation has extended from Pleistocene 

 time down to the present. 



2. ice-beds of elevated pleistocene lake basins not of snow 



ORIGIN 



The older elevated ice-beds as they survive in Alaska today 

 appear to mark the end of the Pleistocene and beginning of the 

 Recent, there being no break between the two periods. This elevated 

 ice marks a colder climate, which accompanied the elevation of the 

 land that drained the large Pleistocene lakes. It also marks the 

 beginning of conditions as they exist today in that region. It is 

 the oldest ice we know of after glacier ice. 



The ice-beds are elevated from fifty to two hundred feet above 

 present drainage levels. They rest on the Pleistocene lacustrine clays 

 in hollows or undulations apparently due to gentle folding the silts 

 have undergone in being elevated to present levels. This same 

 elevation being the one that has caused the Pleistocene lakes to 

 drain. 



As already remarked it is dead ice gradually wasting away and 

 not, from appearances, being added to in any way. Generally it 

 may be distinguished from the younger ice interstratified, or rather 

 intermingled, with the recent alluviums of the river and coastal 

 plains, by its occurrence in more extensive sheets or beds, its eleva- 

 tion above the present drainage levels caused by the down-cutting 

 of the streams since it was frozen, and in that it rests conformablv 



