Its an "underhammer" rifle. There isn't much in print on them. The only comprehensive study was done by Herschel Logan back in the late 1950s. There is a new book coming out shortly on the Ruggles-patent underhammers, the first American Underhammers. At first glance, I thought this might be one of those but, while it is similar, I don't think it is.
Most likely Dewitt is the maker and Morsi an owner. Most of these were made in New England but with a nationwide market in mind so finding one in rural Michigan is completely appropriate. Gardner has several Dewitt's, none listed with the initials "J.P." but one was named James.