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down of their rims and of filling up of their axes, and they thus 

 assumed lower reliefs and flatter lines. The projection of their lines 

 thus modified would not accurately represent the true preglacial lines. 

 If the general glaciation sustained a large ratio, dynamically speaking, 

 to the local or valley glaciation, this modification might introduce an 

 error of some moment. As a matter of fact, however, judging from 

 what we know of the general glaciation of the Alps, it probably was 

 not very material. It is less easy to say what may be true of Norway, 

 where general glaciation was much more important both actually and 

 relatively. 



In the advancing and retreatal stages of the several glaciations 

 another group of influences came into play. The main valleys were 

 filled by glacial tongues which more or less effectually blocked up the 

 mouths of the tributaries, checked erosion in them, and induced fill- 

 ing, as may be seen in many such valleys today in the Alps, in Green- 

 land, and elsewhere. The valley occupied by the Marjelen See may be 

 cited as a familiar and striking example. While the mouths of the 

 tributary valleys were thus blocked up, their rims were being degraded 

 and a change was thus being wrought in their configuration. The 

 effect of this class of action was to give the tributary valleys not only 

 gentler declivities than they had preglacial ly, but gentler even than 

 they would have acquired in the natural degradation of the basin had 

 it remained open and free from ice throughout. The result may be 

 styled a premature maturity, for it was not strictly normal to valleys 

 at such positions in the general drainage system. It was a maturity of 

 a local nature hastened by the establishment of a transient base-level 

 at the mouths of the tributaries by the obstructing ice. 



This special phase of the reshaping of the tributary valleys, being 

 of the erosive type and being aided by the special climatic conditions 

 of the time and by the high declivities of the valley sides, doubtless 

 quite rapidly removed the signs of the previous subduing effects of 

 general glaciation and restored an aspect resembling the preglacial 

 one without being such, and hence made it difficult to distinguish this 

 pseudo-maturity, if it may be so called, from such degree of maturity 

 as had been attained in preglacial times, or, if you please, such an 

 ideal stage of maturity as would have been reached by subserial erosion 

 had not glaciation interfered. A restoration of the preglacial condi- 

 tions of the main valley based on the lines of this pseudo-maturity of 

 the tributaries would obviously involve error v Its amount depends on 



