There is every reason to believe that the Martian snow-caps are quite flimsy structures.

Their material might be called snow _souffle_, since, owing to the small power of gravity on Mars, snow is almost three times lighter there than here.

Consequently, its own weight can have very little effect in rendering it compact.

Nor, indeed, is there time for much settling down.

The calotte does not form until several months after the winter solstice, and it begins to melt, as a rule, shortly after the vernal equinox.