THE MECHANICS OF GLACIERS 91 3 



rate of melting increase as we go down the glacier, and the more 

 rapidly will the flow diminish ; similarly, the steeper the 

 reservoir the more rapidly in general will the flow diminish as 

 we ascend. 



It has been stated as an empirical rule that the velocity of 

 the ice of glaciers lying in beds of uniform slope is greatest in 

 the neighborhood of the neve-line and diminishes as we leave it 

 going up or down the glacier. This rule is, like most empirical 

 rules, subject to exception, and ma)- be stretched beyond its 

 limit, as when Professor Heim (Gletscherkunde, p. 160) 

 attempts to account for the increased velocity near their ends of 

 some Greenland glaciers which break off in bergs, by saying that 

 we have here to do with only the upper part of the glacier ; 

 whereas, in reality, the ends are some distance below the neve- 

 line. The general law that the flow is less below, than at, the 

 neve-line must hold ; this flow equals the product of the aver- 

 age velocity by the sectional area by the effective density. The 

 more rapid surface velocity is permitted by the formation of 

 immense crevasses which reduce the effective density of the 

 upper 200 feet of the ice by perhaps a half. The real and 

 sufficient cause of this increase in velocity is the lack of sup- 

 port in front, which Professor Heim also describes. The flow 

 near the end of such glaciers is not as large as appears at first 

 sight ; it is only the upper part of the ice that has such an 

 abnormal velocity ; the lower part, being supported by the pres- 

 sure of the water, must have a velocity not differing very greatly 

 from what it would have if the glacier completed its course and 

 ended as an ordinary alpine glacier. Indeed, as the increasing 

 velocity at the surface is only permitted by the opening of 

 immense crevasses, so an increasing velocity in the middle and 

 under part of the glacier would also be accompanied by similar 

 openings ; and the whole body of the ice would be so torn by 

 these great fissures, that comparatively thin sheets would be 

 broken off from the glacier's end, and large icebergs could not 

 be formed. The drag of the upper layers over the lower ones, 

 would, in glaciers whose ends are floating, have to be entirely 



