What method does Jem devise to make a snowman?

They used both snow and soil to build the
snowman.

The different layers of snow and dirt seem to give
a bit of foreshadowing of the racial unrest that will shake up the
town.

In the effort to disguise the color of the snow-man
and the likeness to Mr. Avery, Jem runs over to Miss Maudie's house and snatches her hat
and hedge clippers to decorate the snowman/woman.