Shortly after the American Quilt Study Group Seminar, I received a note from Barbara Brackman, who had viewed the chintz medallion while we were in Lincoln. There had been some discussion about the ground cloth. Was it really Marseilles cloth if it was only one layer? Barbara thought it was really something called dimity. When she got back home, she looked through her Florence Montgomery Textiles in America to see if she could find it. She did, and she shared some intriguing details.
In Montgomery, page 218-222, she defines it as any number of harness-loom pattern fabrics. In 1696, dimity of several patterns was used for men's waistcoats and women's petticoats. In 1739, dimity was ornamented in the loom, either with stripes or fanciful figures, when woven is seldom dyed, but commonly bleached of a pure white. Montgomery says from 1750-1825, dimity was pinned with figures. It is the sort of muslin Barbara thinks Austen era women wore, more substantial than a plain weave.
In 1812 in Ackerman's magazine, a stamped (printed?) dimity for white beds and other furniture (prints) was said to want "no lining". The swatches in Montgomery's book are from 1796, and are similar to the ground cloth in my quilt. Marseilles cloth, on the other hand, shares many of the visual characteristics but it is typically more than one layer. So, it looks like what I've got is dimity rather than Marseilles. There are four panels, each about 27" wide. Good detective work, Barbara!