Mariner 9 and Viking Orbiter observations of the topography and mass of layered deposits in the north polar region of Mars suggest a density of about 1 gm/cn3. Consideration of the self-compaction of these deposits further suggests that this low density cannot be explained by a high porosity sediment. Rather, a significant component of ice is probably required to account for the low value. The density further implies that the silicate fraction, regardless of its density (i.e., its composition), represents a volumetrically almost negligible component of the deposit. The most likely values, 5% silicate dust and 95% ice, agree well with a theoretical model for the formation of the deposits through cyclic incorporation of the perennial polar ice cap. Additional tests of this model may be posed in advance of future spacecraft missions to Mars.