78 P. A. ØYEN. 



whether that erosion is caused by a series of local glaciers, or 

 by an ice-cap of a more continental character. In both cases 

 it is the very same phenomenen that is going on before our 

 eyes, and the result is also the very same in both cases, namely 

 a levelling abrasion working down to a certain plane, the clima- 

 tic limit of abrasion, which is at all times exactly accommo- 

 dated to the telluric-cosmic condition of the earth's surface at 

 the place concerned. 



Changed conditions of climate will necessarily be followed 

 by oscillations of the climatic Hmit of abrasion; and as far as 

 this fact is concerned, it will make no difference to which order 

 these climatic changes belong. There are, it is true, certain 

 limits within which climatic elements may oscillate without practi- 

 cally altering the position of the climatic limit of abrasion, and 

 that limit may therefore, during long periods, remain in or about 

 the very same climatic plane, this last term meaning a plane 

 passing through all points that at one and the same moment 

 contain the same climatic value. A climatic plane is, of course, 

 an undulatory one. 



If the climatic plane is sufficiently changed to alter the posi- 

 tion of the climatic hmit of abrasion, we may witness various 

 forms of glaciation and various features of orography, according 

 to the more or less advanced development of abrasion, and accor- 

 ding to the length and amplitude of the oscillation. In the Jotun- 

 heim we meet with a multitude of forms illustrating different 

 stages of orographic evolution. 



Having already viewed the variation of our glaciers geologi- 

 cally, we will now proceed to study that phenomenon as far as 

 historical records can be followed. 



