|Preheat oven to 375*. In a medium bowl toss the flour with the brown sugar, cinnamon, nutmeg, and salt. Using a pastry blender or food processor cut in the butter until the mixture resembles small peas. The topping can be made ahead and refrigerated.
Butter two 13" x 9" baking pans. In a large bowl, toss the blueberries with the peaches then spread the fruit in the prepared baking dishes. Scatter the topping evenly over the fruit and bake for about 45 minutes or until the fruit is bubbling and the top is crisp.
Serve warm or at room temperature with ice cream or whipped cream.