204 T. C. CHAMBERLIN^GLACIAL STUDIES IN GREENLAND. 



layers of debris, which embrace not only sand and silt, but rubble and 

 bowlders. The whole may be likened to a cold sandwich — a meat and 

 mustard of drift spread between slices of ice. Often the interspread layer 

 consists of the merest film of silt ; at other times it attains a thickness of 

 an inch or two, and sometimes it reaches several feet ; but this is rare, and 

 it is then usually a heterogeneous mixture of debris and ice. The debris 

 is usually arranged in very definite and limited horizons, leaving the ice 

 on either hand as clean and pure as any other. It is very notable and 

 significant that the ice next to the debris-layers is the firmest and most 

 perfect ice which the glacier affords. It fractures in sharp, vitreous part- 

 ings, which send forth beautiful iridescent reflections like the purest 

 lake-ice. Seen in place, it appears black because of the dark earth above 

 and below it, but separated from these associations it shows its true 

 nature as clear, transparent ice. Even this ice, however, does not reach 

 the perfection of ice-structure, but it is further advanced toward it than 

 the great mass of the glacier. 



Debris-layers and Lamiinx. — The coarser debris is arranged in the same 

 horizons with the fine debris. Often a fragment of rock will be several 

 times as thick as the average silt-layer with which it is associated. In 

 this case it is usually centered on the layer and projects above and below 

 into the clean ice. In this way bowlders of considerable dimensions may 

 be associated with a mere film of fine debris. More frequently, perhaps, 

 the larger fragments are associated with laminated bands rather than 

 with single laminae, and in this case it is interesting to observe that a 

 portion of the laminae curve downward and pass under the bowlder, while 

 another portion curve up over it. Sometimes all the laminae part and 

 pass around on either side ; in other cases those which encounter the 

 center of the bowlder terminate there. Usually corresponding laminae 

 appear on the other side. The phenomenon is almost precisely like the 

 behavior of silt-laminae in stony sediments. (Figure 4, plate 4, and figure 

 13, plate 9.) 



The debris-layers are not at all uniform in their distribution. Often 

 they have much regularity and persistence ; often they thin out and dis- 

 appear within a short distance ; more often still they persist for a few 

 rods and are replaced by adjoining layers which come in as these thin 

 out. Thus a belt of layers has much persistence, while the constituent 

 layers are freely entering and vanishing. Lenses of debris occasionally 

 appear among the layers, and a doubling back of the layers upon them- 

 selves, giving a lenticular section, is not uncommon. 



The laminae are sometimes very symmetric, straight and parallel, but 

 often they are wavy and undulatory. In many instances they are greatly 

 curved and sometimes contorted in an intricate fashion. As Dr. E. von 



