The Jimberlana Norite Intrusion, situated near Norseman, Western Australia, is the first real analogue of the Great Dyke of Rhodesia to be discovered. The intrusion has the external form of a dyke, extends for at least 180 km (112 miles), has a maximum width of 2.5 km (1.5 miles), and follows the general easterly trend of the other members of the Widgiemooltha Dyke Suite, all of which have so far revealed characteristics of true dykes. It has a very steep funnel-shaped cross-section, like the Great Dyke, and shows many internal, canoe-shaped complexes along its length, consisting of cumulate ultramafic and basic rocks together with minor acid differentiates. The ultramafic and basic rocks display phase, rhythmic and cryptic layering. The differentiation sequence from ultrabasic to basic rocks is repeated more than once, and therehave clearly been several pulses of magma up the tensional opening. This is confirmed by the recognition of at least two magmatic unconformities. The broader petrogenetic questions posed by this unusual intrusion are discussed.