This letter was not published. It is in Forrest 1974, who evidently got it from Pearson II, but Pearson only states that Galton sent a letter to the Gazette, which did not publish it. The letter was in response to a complaint published in the Gazette about burials in the Abbey. A search through adjacent numbers shows no letters by Galton on the subject.
Burials in the Abbey.
Pall Mall Gazette