PURPOSE OF THE PAPER 15 



as if the extreme differences of opinion and the sudden and radical 

 shifting of views were not creditable to the science. The work of recent 

 glaciers in varied forms is conspicuous over vast territories, and living 

 glaciers are available for comparison in large numbers and of various 

 classes and conditions. This diversity and changing of views suggests a 

 psychological phenomenon more interesting perhaps than the glacial. 

 It implies either some unusual, peculiar, and indefinite character of the 

 glacial phenomena, or failure in accurate observation, or faulty interpre- 

 tation of the facts. 



Purpose of the paper. — The original plan of this writing was to present 

 the arguments and conclusive facts against great ice erosion in central 

 and western New York. It was, however, found desirable to preface the 

 discussion with a review of the general theoretic problem. The paper 

 has therefore been expanded into a general consideration of the whole 

 problem, and will try to aid in establishing a sound conclusion on this 

 much-disputed subject. The truth is desirable, even though it destroys 

 the pleasure of disputation. 



Use of the term "erosion" — One of the sources of disagreement in this 

 study has been the failure to discriminate the several forms of ice erosion, 

 to recognize its limitations, and to use a distinctive terminology. It will 

 be necessary not merely to save circumlocution, but as aid in clear think- 

 ing, to make distinctions and to explain the use of terms. 



It is conceded that glaciers have power to gather up and carry along 

 loose material which they find in their way, and that they frequently, 

 but not always, exercise that power. It is conceded that they can push 

 awa} r loosened blocks which obstruct their paths, and may thus to some 

 extent cut down opposing cliffs or ridges ; also that they can " pluck " or 

 pull away loosened blocks, under some conditions. It is also granted 

 that glacial ice may lift and bear away layers of stratified rocks which 

 previous weathering has detached or loosened. It may be conceded that 

 at the feeding grounds of alpine glaciers the valley heads may be ex- 

 panded into cirques and the walls steepened, by the aid of weathering, 

 through the pull of the ice on the frost-loosened blocks, specially where 

 facilitated by vertical jointing. It may even be conceded that the ice 

 may rend or tear away the weathered material so as to leave an irregular 

 surface with shallow rock-basins, specially in crystalline rocks ; and as 

 a further concession it may be admitted that alpine glaciers can possibly 

 do some basin-making work at the foot of steep slopes or cascades of the 

 ice in unobstructed valleys, analogous to the basins made by the plunge 

 of cataracts. In brief, it is granted that glaciers may produce com- 

 paratively small and shallow rock-basins in weathered crystallines, and 

 rarely in mountain valleys, while it is generally recognized that glaciers 



