EXISTING GLACIERS. 29 



This manner of the production of icebergs differs 

 from that which has been ordinarily represented in the 

 text-books, but it conforms to the law of glacial motion, 

 which we will describe a little later, namely, that the 

 upper strata of ice move faster than the lower. Hence 

 the tendency is constantly to push the upper strata for- 

 wards, so as to produce a perpendicular or even projecting 

 front, after the analogy of the formation of breakers on 

 the shelving shore of a large body of water. 



Evidently, however, these masses of ice which break 

 off from above the water do not reach the whole distance 

 to the bottom of the glacier below the water ; so that a 

 projecting foot of ice remains extending to an indefinite 

 distance underneath the surface. But at occasional in- 

 tervals, as the superincumbent masses of ice above the 

 surface fall off and relieve the strata below of their weight, 

 these submerged masses suddenly rise, often shooting up 

 considerably higher than they ultimately remain when 

 coming to rest. The bergs formed by this latter process 

 often bear much earthy material upon them, which is 

 carried away with the floating ice, to be deposited finally 

 wherever the melting chances to take place. 



[Numerous opportunities are furnished about the front 

 and foot of this vast glacier to observe the manner of the 

 formation of fcames, kettle-holes, and various other irregu- 

 lar forms into which glacial debris is accustomed to ac- 

 cumulate. Over portions of the decaying foot of the 

 glacier, which was deeply covered with morainic debris, 

 the supporting ice is being gradually removed through the 

 influence of subglacial streams or of abandoned tunnels, 

 which permit the air to exert its melting power under- 

 neath. In some places where old moulins had existed, the 

 supporting ice is melting away, so that the superincumbent 

 mass of sand, gravel, and boulders is slowly sliding into a 

 common centre, like grain in a hopper. This must pro- 

 duce a conical hill, to remain, after the ice has all melted 



