C4LACIAL EROSION. 



93 



smooth, but are as rough aud as much weather- worn as similar rocks in warmer countries 

 where no glaciers have been. Upon these surfaces, it is often difhcult to discover 

 scratches — even when present — for they are often so faint as to be only rendered apparent 

 by moistening the rock. Even the faces of the hummocks are commonly imperfectly 

 polished. In other places, particularly at Tunsbergdalbrseen which contains much sand 

 along the margin, the rocks are highly polished, and but little scratched. One is every- 

 where stirprised to find beneath the glaciers the great paiicity of glaciated stones, aud in 

 many terminal moraines they are scarcely, if at all, to be found. 



The insufficiency of glaciers to act as great erosive agents is farther shewn at Fon- 

 dalen (fig. 4), where a mass of ice thirty or forty feet thick abuts against a somewhat steep 

 ridge of a rock, ten feet or less in height. In place of a stone-shod glacier sliding up and 

 over the barrier, the lower part of the ice appears stationary, or else is moving around the 

 barrier, while the upper strata bends and flows over the lower layers of ice (along the 

 line M, fig. 4). 



Fin. 5. — End of Svartisen glacier at head of Holandsfjord, moving through a lake against morainic barrier. 



When the barrier to the advance of a glacier is met with, whether composed of hard 

 rock, or of morainic matter, the ice, provided it be sufficiently high, flows over upon itself, 

 yet when the sheet is no higher than the barrier, the lateral thrust may push it up some- 

 what. The best example of the consequences of such a condition is to be seen at Svartisen 

 glacier, at the head of Holandsljord, which descends to within sixty feet of the sea 

 where it ends in a morainic lake of considerable size, the northern side of which is filled 

 with the glacier. The water of the lake rises, in part, to the level of the ice, or over it, 

 where the waves of the lake are depositing sand upon its surface. Part of the ice is not 

 less than twenty-five feet thick, and most of it is probably double that thickness. Some 

 of the strata of ice are pushed iip and rest at 5° from the horizontal. But the interesting 

 points are at the end of the glacier, where it impinges against the morainic barrier. 

 Being unable to advance, the lateral pressure has forced up an anticlinal ridge or rather 

 dome in the ice, to a height of fifteen feet, along whose axis there has been a fracture and 

 fault. Upon this uplifted dome rests the undisturbed sand stratified in perfect conform- 

 ity to the surface, which was formerly just below the level of the lake As the ice 

 about the line of fracture melts, the sand falls over aud leaves a sand cone, of which there 

 were examples — one at the end of the lake, and two in the centre, — but the nuclei of the 

 mounds were of solid ice. By this lifting process, pockets of loose clayey sand were 

 thrown on top of the morainic matter, producing thus the appearance of having been 

 ploughed up by the glacier, to even several yards beyond its termination, which has not 

 been the case. 



