This section of the novel occurs in Chapter Eight, and is when, rather disappointingly, Jem has to concede that it is not snowing hard enough to yield enough snow in order to make a snowman from the snow that has landed in his garden. However, never the one to be put off by such facts, Jem determines to take the snow from Miss Maudie's garden, asking her permission to take it and transfer it back to his own yard. Even then it is clear that there is not enough snow. Jem therefore collects equal amounts of earth, and uses this soil to construct the first layer of the snowman that they make, before finally using the snow to cover up the earth to give the appearance that they have made a snowman, which bears a rather uncanny resemblance to Mr Avery:
Jem scooped up some snow and began plasting it on. He permitted me to cover only the back, saving the public parts for himself. Gradually Mr Avery turned white.
In a novel that is so much about racism and the importance of the colour of one's skin, having a snowman that is black underneath and white on top points towards the superficiality of such distinctions, and suggests a common humanity that is shared by all, no matter what the colour of the top layer of skin somebody has. Note too, that the snow that falls is incredibly unseasonable and something of a hostile intervention of nature. This, along with the fire that burns Miss Maudie's house, threatens the characters, but the characters are able to use their natural goodness and potential to convert this threat into an opportunity through their goodness. The significance of the snowman is through the way in which Jem uses black earth to build it and how this links to the theme of racism in the novel.
In Chapter 8 of To Kill a Mockingbird, it begins to snow in Maycomb. Only a small amount is sticking to the ground, so the children are very careful as to where they walk, concerned that their footsteps will reduce the amount of snow on the ground that could be used to build a snowman.
Scout follows Jem to Miss Maudie's yard, and they ask her if they can "borrow" some of her snow. They take baskets and begin to rake the snow up. Jem also begins to dig up earth. Ultimately they fill five baskets of earth and two baskets of snow. Jem then begins to build a snowman by first piling the dirt and shaping it into a torso that he can make white by covering with snow.
Jem ran to the back yard, produced the garden hoe and began digging quickly behind the woodpile, placing any worms he found to one side. He went in the house, returned with the laundry hamper, filled it with earth and carriedit to the front yard. When we had five baskets of earth and two baskets of snow, Jem said we were ready to begin.“Don’t you think this is kind of a mess?” I asked.“Looks messy now, but it won’t later,” he said.Jem scooped up an armful of dirt, patted it into a mound on which he added another load, and another until he had constructed a torso.