120 REGINALD A. DALY 



summit-level accordance is to be sought in a special, characteristic 

 control of alpine climates. In general, the climate of high levels 

 is a glacial climate. In general, glacial erosion is very great and the 

 bulk of it is high-level erosion. In general, local glaciers and glacial 

 erosion are most abundant and long-lived about the highest summits. 

 One net result of glaciation is to cause the specially rapid wastage 

 of those summits and to produce rough accordance among the peaks. 



4. The influence of the forest cap on Summit altitudes. — Climate 

 not only breeds glaciers in the high levels of an alpine range ; it nor- 

 mally determines a more or less well-defined tree-line. The treeless 

 zone is always more extensive in area than the glacier-bearing zone, 

 but the upper limit of trees is often not far from coincident with the 

 lower limit of the zone of cirque glaciers. It is logical to find here 

 a place for the theory that widespread accordance of summit levels 

 in an alpine range is related to the differential rate of erosion above 

 and below tree-line. The theory is so well known that it needs no 

 special detailed statement in the present paper. Let it suffice to 

 recall the principal reasons why denudation is faster above tree-line 

 than below, and once more note the inevitable conclusion from that 

 fact. Again we must take care to adopt the highland view of erosion. 

 It cannot be too strongly emphasized that the conditions of rock 

 destruction and transportation are vastly different from what they 

 are at lower levels. It is only partially correct to discuss in terms of 

 falling water the degradation of mountain slopes, whether tree- 

 covered or not. Their degradation must chiefly be discussed in 

 terms of falling rock-waste. In the lowlands stream corrasion has 

 its maximum of destructive influence. Among the high mountains 

 stream corrosion has a minimum of destructive influence. The 

 analysis of high-mountain degradation deals, on the one hand, with 

 the methods of rock-disintegration, and, on the other hand, with 

 the methods of carrying the resulting waste out to the lowlands. 

 The complete analysis, waits on the discovery of quantitative data. 

 We have here another instance of the need of sharpening and extend- 

 ing the highland view. Yet the qualitative data already recorded 

 leave no doubt as to which zone is the more rapidly degraded. 



a) Disintegration of rock. — A striking proof that Anglo-Saxons 

 have only recently begun to take the highland view appears in the 



