Oops, I believe you asked for marshmallow icing, too. Again, it's from the 1940 cookbook.

Marshmallow Icing
2-1/2 c. sugar
1/2 c. light corn syrup
1/4 t. salt
1/2 c. water
2 egg whites
1 t. vanilla
8 (1/4 pound) marshmallows

Cook sugar, corn syrup, salt and water together (without stirring) to 250 degrees F. or until a small amount dropped into cold water will form a firm ball. Pour the hot syrup slowly over stiffly beaten egg whites, beating constantly. Add vanilla and continue beating until frosting is cool and thick enough to spread. Add marshmallows, cut into eighths. Will cover top and sides of 3 -- 9" layers.