I think it was probably something more like Jello: http://www.bbcgoodfood.com/howto/guide/great-british-jelly IIRC gelatin desserts are called "jelly" in some old books, altho to us modern readers it means fruit preserves (and does in Little Women too - maybe a UK-type thing?). Since it was in a 'glass' it was probably cut into shapes or cubes, like how Jello squares are served in tumblrs today. Think something like blancmage (or, shudder, ASPIC).