A quantitative model which takes into account the temperature dependence of magma viscosity is developed to describe the distribution of cumulate crystals in a sill after its solidification, and is compared with natural examples. A precise comparison is not possible as data on the size-distribution and concentration of the cumulate crystals are not available. However, a preliminary analysis suggests that although several major features can be explained the simple model of crystal settling cannot account for the details of the olivine distribution in the Palisades sill and the Uwekahuna laccolith.