Good friend, Jonathan Bach looked up Hilda Nagel, the name on the gravestone in one of the photos from Holy Hill. He found her listed only as the wife of Rev. A. Nagel in a 1910 directory called “List of Protestant Missionaries in China” under the heading for “Basel Missionary Society, Hong Kong, Lilong”. http://divinity-adhoc.library.yale.edu/Resources/Directories/1910_Directory.pdf. He was then able to find the above photo of Rev. A. Nagel titled “Pupils of the Boy’s Boarding School in Lilong (China)” with an annotation “Teacher Tschong, the missionary Nagel, Teacher Tschin”.
Indeed, for those interested in old photos from the Basel Mission, the USC Digital Library International Mission Photography Archive is a fabulous resource.