Hi Dorothy,
Sounds like a great find! I just sold one Bennington mug today for $12.74 with the dg mark. That stands for David Gill and I do believe these are worth more, as from what I've read he started Bennington Pottery. Good luck!
Here's the link to my mug listing:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=180443815074Vicki