Glaciers are defined and often popularly referred to as streams of ice. In shape and in the fact that they run downhill, they are like streams of water, but there most similarity ends. Glaciers are aggregates of ice which move slowly. The effects of glaciations, like those of all other surface processes, are erosion of the highlands and filling of the low places. There is therefore both abrasion and deposition.
There are very significant differences between the behavior and the properties of glaciers and streams. A glacier is an accumulation of crystalline solid ice. It is essentially a rigid body. A river is a stream of liquid which has no rigidity, which has none of the properties of a solid. A glacier can support upon and within itself masses of rock which are of greater specific gravity than ice; streams cannot carry in suspension large masses of materials of a higher specific gravity than water. Water can never run uphill; glaciers can move uphill very commonly. Water which meets loose materials flows over or around it, while ice can push this material in front of it. Water will run over a cliff in a continuous stream; ice in such a circumstance breaks into separate pieces which fall as individual blocks, broken from a solid mass. Water which flows slowly over an uneven surface conforms itself to its irregular bed; a glacier going over irregularities cannot bend and therefore cracks. These differences directly result from the fact that a river is liquid and a glacier is a rigid, crystalline solid.