Preheat oven to 350 degrees.
Prepare cake mix as directed on package.
Pour 2 cups batter into greased 13 x 9 inch baking pan.
Bake 15 minutes.
In heavy saucepan over low heat melt caramels and margarine.
Remove from heat; add condensed milk.
Mix well.
Spread carmel over cake.
Spread remaining cake batter over carmel.
Top with nuts.
Bake 30 minutes or until cake springs back when lightly touched.
Cool.