1. Combine cracker crumbs, melted butter and 1/4 cup sugar. Blend well and press on bottom and sides of a 9-inch pie plate.
2. Put blueberries through a sieve or a food mill; sweeten with 1/3 cup sugar. Let stand while whipping the cream with corn syrup until mixture holds its shape.
3. Turn cream into piecrust and pour blueberry mixture in a thin stream over top to create a marbled effect. Freeze. Cut into wedges to serve.