Thank you SO much, Cancan, and Dennis, and others who have offered extremely interesting information about the conditions at the St. Paul, Walkden Churchyard, and even offered to go take a look. I also heard today from Helen Mayoh, who more or less confirmed our worst fears. She said that if Thomas Collier Marshall's name isn't on the MI (Index) list for that Church, it is most likely there is no headstone.
Sadly, too, she told us that many of the headstones have been subject to vandalism: pushed over face down, and therefore unreadable. A lot of them must be very heavy. One can only question the mentality of these vandals who would do such things, and ask WHY?? WHY?? WHY??
Anyway, it looks like, there may be no point in searching for Thomas Collier Marshall's headstone if there isn't one, or one that has been pushed over. Unfortunately, the Marshall names you mention, Dennis, do not seem to be connected with our Marshall family at all. Even Thomas's wife, Mary, remarried not long after his death, and lived a long life with her second husband, so she was not buried with him. Thomas's father Henry was killed on the Somme in WWI, and we do not know where he is buried. Perhaps somewhere in France. The rest of our side of the family ended up living in Huddersfield, Yorkshire, a long way in miles and thought from Walkden and Grandad's grave, and those who passed on were buried in Woodhouse Churchyard in Sheepridge, Huddersfield.
So... as much as we have appreciated all the input concerning Thomas Collier Marshall's grave, I think we have come to the end of the line with it.
Thanks again, everyone, for all your help.
Sincerely,
Tom and Jan M