782 ROLLIN D. SALISBURY 



These relations led to the conclusion that the overhang in 

 this, as in other cases, was the result of unequal melting, due to 

 the unequal distribution of debris. The debris, being dark 

 colored, absorbs the heat to a greater extent than the clean ice, 

 and the ice behind the debris is therefore melted back more 

 rapidly. As the thin zone which carries the debris is melted 

 back, the water trickling down the face of the ice below carries 

 the earthy matter with it. The ice just below the debris zone is 

 coated with the finer materials washed down, and for this reason is 

 melted back more rapidly than clean ice, and most rapidly where 

 the coating is thickest. This causes the layer just below the 

 debris zone to be melted back, on the whole, faster than the 

 layer above, and to recede most rapidly at the debris level. This 

 gives rise to the phenomena seen in Fig. ii. 



Stratijl cation and veinmg of the ice. — One of the conspic- 

 uous features of the ice of north Greenland is its distinct and 

 often very conspicuous stratification (see Figs. 3-7 and 11), 

 though there is much arrangement in layers which is not strat- 

 ification, in the proper sense of the term. The layers (and veins) 

 may be horizontal or vertical, or inclined at any angle. The 

 arrangement of the vertical layers (veins) may be longitudinal 

 or transverse, with reference to the glacier. 



The presence of debris between the horizontal or approx- 

 imately horizontal layers often helps to emphasize their distinct- 

 ness, but their existence is not the result of the presence of 

 debris. Certain layers of the ice are more solid (and blue), and 

 certain other layers are more porous (and white). It is upon 

 the varying texture of the different layers that the stratification 

 in the upper part of a glacier is usually dependent, while the 

 debris often emphasizes the distinctness' of the layers in the 

 lower portion. The horizontal layers or laminae of ice are of 

 variable thickness, and it would appear that the melting of ice, 

 like the weathering of roclv, often develops laminae within layers 

 which, in a firmer condition, appear massive. The number of 

 laminae is often as much as eight or ten to the inch, at the same 

 time that layers several feet in thickness do not, in a solid con- 



