COMPARISON BKT'n MAINLAND AND GREENLAND GLACIATION. 201 



Our drift, oxcei^t on the eastern border and tlie Cordilleran tract, is 

 spread upon a vast plain. The ice-tields of Cireenhmd rest mainly upon 

 plateaus fringed by rugiijed mountains. To learn how a Cireenlandic 

 glacier would behave on our plains the etlects of broken topography 

 must l)e escaped or eliminated. Simple elevation, however, is immaterial. 

 A plateau of smooth surface may furnish conditions identical witli a 

 ])lain, so ♦ar as glacier behavior is concerned. It is only necessary that 

 tlie glacier deploy freely on relatively smooth ground and come to a limit 

 by the balance of growth and wastage. It was extremely desirable, 

 therefore, to lind a portion of Greenland whose border was free from 

 mountains. Inglefield gulf, perhaps better than any other portion of 

 Greenland, furnishes the desired conditions. Unlike most of the coast, 

 it is not girt by mountains. The borderland is a plateau about 2,000 

 feet above the level of the sea, with a summit-plain of marked uniformity. 

 Its undulations are intermediate in strength between those of the eastern 

 and western })arts of our own glacial field. The border of the great ice- 

 sheet may there be studied on relatively smooth ground, or it may be 

 studied on undulator}^ ground, or the lobes or tongues that descend into 

 the valleys may be chosen. In the portion in which my chief studies 

 lay only a very small fraction of the ice was discharged into the sea. 

 The border would in no appreciable way be changed were there no sea- 

 wastage at all. Glacial tongues from one to three miles long are fre(iuent, 

 but it does not appear that the nature of the main ice-border would be 

 essentially different if the valleys that caused these tongues had been 

 absent. 



The peninsulas of the region have local ice-caps from which glaciers 

 radiate as from the great ice-cap. The habits of the small and the great 

 ice-caps are essentially the same. 



Of tlie 30 or 40 irlacial tongues which descend toward Inglefield <rulf 

 less than one-third reach the shore, and scarcely one-half of these dis- 

 charge notable icebergs. The majority terminate in valleys whose bot- 

 toms are farmed of glacial debris and whose lower gradients are moderate. 



Uklation of f;KOLOGic P\:)UMATioNs OF Greenland to Glacl\tion. 



The geologic formations of Greenland are unfavorable in the main to 

 glacial studies. The nearly universal j^resence of the ancient gneissic 

 series makes discrimination of the origin of material unsatisfactory, when 

 it is not impossii)le. besides this, the de))ris is rocky and arenaceous; 

 the clayey element is scant. 



In the Disco and Ingledeld gulf regions, however, the gncn'ssic series is 

 l»ordere<l by clastic and igneous l)e(ls that give some relief from these 

 adverse conditions. On Disco island there is a nucleus of gneiss sur- 



