GLACIER TRANSPORTATION 113 



and rounded into the form called "rSches moutonnees" with the 

 side upon which the ice impinged gently sloping and polished, but 

 with the down-stream side abrupt and often not ice worn. 



On a large scale, glacial erosion produces rounded and flowing 

 outlines of hill and valley, cutting hard and soft rocks alike 

 (instead of leaving the harder standing in relief), and producing 

 forms which are in marked contrast to the craggy and rough 

 topography of unglaciated regions. 



River action may polish hard rocks by scouring them with sand, 

 but the glacial furrows and parallel striae cannot be imitated by 

 other agents. To find these characteristic marks of ice, it is not 

 necessary to visit actual glaciers ; the northeastern quarter of the 

 United States, from the Mississippi to the Atlantic, displays them 

 in abundance, where harder rocks are exposed on the surface. 

 The rounded forms, the parallel striae, the polished surfaces, are 

 common where the rocks are hard enough to retain the markings. 



Glacier Transportation. — The transporting power of a glacier 

 is not determined by its velocity, at least so far as the material 

 carried on its surface is concerned. This is because the rocks 

 may be regarded as floating. bodies with reference to the ice, and 

 thus a rock weighing many tons is carried with as much ease as a 

 grain of sand. The masses of material transported by a glacier 

 are known as moraines. The moraines which are carried on the 

 top of the glacier are derived from the cliffs and peaks which 

 overhang the ice, and the action of frost and landslips is con- 

 tinually showering down earth, sand, and rocks of all sizes, from 

 small blocks up to masses the size of houses. This material is 

 heaped up along the sides* of the glacier in disorderly array, and 

 here forms the lateral moraines. When a glacier is composed of 

 branch streams, it will have a corresponding number of medial 

 moraines (see Fig. 37), in the middle of the glacier. When two 

 branches unite, their coalesced lateral moraines form a single 

 medial moraine. 



The quantity of material thus carried on the top of the glacier 

 depends upon the amount of rock surface which extends above 

 the level of the ice and is subject to the action of the ice and 



