Morphological and morphometric analyses of diamict-dominated and rock-cored drumlins in the Omagh Basin, north central Ireland, identify five drumlin types (classical, shield, barchanoid, fused and superimposed) on the basis of outline morphology and topographic setting. Diamict drumlins are mainly of classical or fused type and are found in lowland and basinal locations. Rock-cored drumlins are more morphologically diverse and occur on high-level plateaus and upland flanks. Morphometric analysis reveals both spatial and statistically significant absolute differences between the elongation ratios and orientations of diamict and rock-cored drumlins. Equifinality of the drumlin form despite variable thicknesses of diamict (from a few metres to>30 m) suggests that substrate streamlining took place in several phases, including eroding bedrock into rock-cored drumlins prior to diamict deposition. This means drumlinization cannot be attributed to a single set of subglacial processes or a single time-interval.