Unable to locate the copyright holder!

[Iris]

Hello,

I am a PhD student intending to publish a scholarly article that has been accepted by a famous journal in my field of research.
I wish to include in the article a map that I have adapted from an original map published in a book dating from 1968 (This was the book's second edition; the first one dates from 1891). The book's publisher (F. Cass) has since then been bought by the Taylor & Francis group, that is why I asked permission from the latter to publish the adapted map.
Taylor & Francis were unable to trace the work/copyright owner as belonging to them. They recommended me to use a copyright disclaimer and fully acknowledge the original publication.

Could you clarify what it means to use a copyright disclaimer?

I should perhaps add that the book's author died in 1953 (less than 70 years ago), and that he did not clearly identify any other author/creator with regards to the map (in the book's acknowledgments).

Thank you and best wishes,
Iris

[Warlock]

Well disclaimer means a renouncement of rights or claim, so I imagine that the simply mean that when you write your copyright notice you explicitly state that this copied work is not your own and acknowledge the source.

I.e. copyright © 2008 Iris, (except [name of copied content], originally published by F. Cass, owner unknown).