The Morin Anorthosite (Grenville province, Canadian shield) occupies the centre of a recrystallised and deformed plutonic complex. Density measurements on selected specimens and density calculations from chemical analysis have shown that such features as layering in basic and intermediate rock, and plagioclase xenocrysts in acidic rocks can be interpreted as having participated in magmatic processes of gravity accumulation and convection currents. Thus, mechanical differentiation in this complex is not basically different from that of well-known layered complexes. The relatively low viscosity that would seem to be required in such processes is in conflict with the high-viscosity type of intrusion that can be deduced from field observations. One way to reconcile these two conflicting concepts is by proposing a model in which the time of consolidation is long enough for gravity accumulation and convection currents to operate, even in a highly viscous magma. This condition can only be attained in catazonal environment. The viscosity of the differentiating magma could be, in this model, of the order of 1013 poises.