Debbie--
Try
Marbles: Identificationand Price Guide. Robert Block. Altgen PA: Schiffer
Publishing Ltd, 1996.
or
Aggies, Immies, Shooters and Swirls: the Magical World of Marbles. Marilyn
Barrett. Boston: Little Brown and Company, 1994.
Both found at Barnes and Noble here in Oakland, CA. Each has a good
bibliography and lots of pictures.
I'd like to get a copy of the article that Carl Steen suggested, but will look
for it here first.
Celia McCarthy