Dissolve the cherry gelatin in the hot water. (If needed, heat mixture until gelatin is completely dissolved.) Stir margarine into hot gelatin until melted.
Allow mixture to cool to a thick syrup.
Beat egg white to soft peaks.
Continue beating the egg white, and pour the gelatin mixture in a thin stream into it. (Mixture will not fluff up.) Place rice cereal in a large bowl.
Thoroughly fold egg white gelatin mixture into cereal.
Pit cherries and chop into small pieces.
Fold chopped cherries into mixture.
Transfer to a lightly greased 13 x 9 in. (33 x 23 cm) cake pan.