June 22, 1835 Frances mentioned to her friend William Irons that she had picked up a pebble on "Diadem Hill" at Annesley in memory of "my friend in early life, Byron's Mary." Both Byron and Mary were deceased by this time.
"Byron" was George Gordon Lord Byron, heir of Newstead Abbey and the celebrated poet. "Mary" was Mary Ann Chaworth, heiress of Annesley, the estate adjacent to Byron's. Mary was older than Byron, but he fell in love with her when as a child he first saw her. He visited Annesley frequently. However, Mary was in love with John Musters, and when she married him, it supposedly broke Byron's heart. He wrote a famous poem, "The Dream," about Mary and their relationship, and in the poem he mentioned being on "Diadem Hill" with her while she watched for John Musters.
Earlier, Frances had written to Irons, "The 'Diadem' is cut down and universally deplored." Washington Irving had a hand in the "universal" disgust. He had visited Annesley and swallowed the old housekeeper's story that Mary's and Byron's lives were ruined by her marriage to John Musters. Irving's account was widely read, so when Mr. Musters (who was Frances' host about the time she wrote this letter) cut down the trees on Diadem hill, he was thought to be acting vengefully.
Frances and Sophie Musters (John and Mary's daughter) knew better and planned together to have the facts brought to light, but Sophie's marriage prevented the project's completion.
What was the truth concerning Mary's marriage to John? What was the real reason Mr. Musters cut down the trees? That can be found in Frances Rolleston: British Lady, Scholar and Writer of Mazzaroth in the chapter "On Trees and Poetry."