Berry Crisp

My mother-in-law has some delicious berry recipes, including this one, and she's been very generous over the years in providing us with quarts of her home-canned berries to make them with. Yum!

        Pour quart of berries, including juice, into a 9x13 pan. Add one large can (29 oz.?) sliced peaches which have been DRAINED and cut up into bite size pieces. Sprinkle generously with ½ to ¾ c. sugar. Stir in about 1 ½ Tbsp. cornstarch. You can warm it up in the microwave for a couple of minutes to start it thickening, but this step is not absolutely necessary.
        In a separate bowl, combine:
1 c. oats
1 c. packed brown sugar
½ c. flour
½ tsp. cinnamon
½ c. margarine or butter.
        Cut margarine in until the mixture resembles coarse crumbs. Sprinkle topping over filling. Bake at 375° for 35-40 minutes or until topping is golden and filling is bubbly.