Streamlined landforms such as drumlins are often formed by erosional  and  depositional processes  working in tandem.  Drumlins may have a rock core with till forming the tail, or may be composed completely of till.  Drumlinoidal features are most often formed in an ice sheet environment.  Tills originating in an ice sheet environment tend to be finer than tills that originate in alpine valley glaciers.  Finer tills have less pore space and are thus more cohesive when they are deposited, and are better for forming drumlinoidal features. 

schematic after Alan S. Trenhaile, The GeoMorphology of Canada, p. 100.