INTRODUCTORY : ICEBERGS AND THE ICE-FOOT. 11 



of regions of present and former glaciation, is, that glacier ice has but little 

 erosive power, and that the so-called "ground moraine" is an appendage 

 of the glacier which is neither characteristic nor important. The present 

 shrinking of the Alpine glaciers shows that there has been usually but little 

 detrital material under them ; and this has resulted not so much from the 

 ice as from the water, which everywhere acts jointly with the ice in doing 

 its work ; indeed, the latter eifects nothing absolutely characteristic, except 

 the production of large areas of polished rock surfaces etched with fine 

 parallel striations, a result which water alone is unable to bring about. 



The action of icebergs in regard to striation of rock surfixces, and more 

 especially the transportation of detritfil material, is a subject of interest in 

 this connection. From the very beginning of the discussions on these sub- 

 jects tiiere has been a marked amount of discrepancy of opinion in regard to 

 the relative importance of glaciers and icebergs as geological agents, and 

 as to the exact nature of the work done by each. Icebergs are born of 

 glaciers,* so that the connection between the two is necessarily an intimate 

 one, and the former may be said in their new condition to be simply floating 

 glaciers. That the iceberg when detached from the glacier is often heavily 

 loaded with detritus is a fiict well known from abundant observations, and 

 one which might be inferred without observation from the very nature of 

 the case. That these floating detritus-carriers are able to transport their 

 burdens to great distances, as they are moved by the winds and ocean curi^ents 

 into which they are borne, is also clearly imderstood. That such detritus, as 

 accumulated along the route of the icebergs, will have a morainic character, 

 — that is, will be angular and irregularly mixed, — is easily recognized. But 

 no true moraine will be formed by icebergs, because they are not held to one 

 exact course, as is the glacier enclosed between its rocky walls ; while there 

 must also be great irregularity in the distribution of the material left by 

 icebergs, because they float with irregular course, according to the varying 

 nature of the winds and currents, and because they are more or less rapidly 

 melted, according to their size and their exposure to meteorological con- 

 ditions which in their very nature are unstable. 



The so-called "ice-foot" also acts, to a considerable extent, the part of the 

 glacier, lor it receives, when suitably situated, a considerable amount of 

 falling detritus, and when loosened by the summer's heat floats oft' and bears 

 this material away, iceberg fashion. 



* The formation of an iceberg is familiarly known in Greenland as tlie "calving" of tlie glacier. 



