Fill a 9” round cast iron skillet or pie pan with sliced peaches and blueberries. Sprinkle sugar evenly across the top of the fruit. Add about 1/2 - 3/4 cup of water to the dish. (The water should come approximately ½ way up the dish.)
Sprinkle the nutmeg and cinnamon on top of the sugar.
In a small bowl, cut the butter into the cake mix until butter is approximately pea-sized. Sprinkle this mixture evenly across the top of the cobbler. (There should be enough topping to just cover all of the peaches.)
Bake at 350°F for 65-70 minutes, or until top of the cobbler turns deep golden brown in color. Allow cobbler to cool for 10-15 minutes before serving.