Marble Sliced Loaf Cake with Vanilla-flavored Icing, Vanilla

cake: sugar, enriched wheat flour (wheat flour, niacin, reduced iron, thiamine mononitrate, riboflavin, folic acid, soybean oil, water, semisweet chocolate chips (sugar, chocolate liquor, cocoa butter, dextrose, soy lecithin, salt, natural flavor, butter (cream, natural flavor, buttermilk (cultured lowfat milk, nonfat milk, food starch-modified, sodium citrate, locust bean gum, carrageenan, salt, vitamin a palmitate, vitamin d3, dry whole milk, food starch-modified, cocoa processed with alkali, wheat starch, leavening (sodium bicarbonate, sodium acid pyrophosphate, monocalcium phosphate, natural flavor, salt, soy lecithin, xanthan gum, citric acid, cellulose gum. icing: icing sugar (sugar, cornstarch, buttermilk (cultured lowfat milk, nonfat milk, food starch-modified, sodium citrate, locust bean gum, carrageenan, salt, vitamin a palmitate, vitamin d3, butter (cream, natural flavor, palm oil shortening, corn syrup, guar gum, natural flavor