The annual Letter Books comprise 19 volumes, which contain primary copies of all of HYL Brown’s early work-related correspondence written after 1882, in his official capacity as SA Government Geologist, to his employer the SA Minister of Mines, plus later letters also written thus (through Brown) by his initial few qualified colleagues working in the fledgling SA Department of Mines from approximately 1904 to 1923. This record series content is of considerable historical importance. For the first 30 years of geoscientific work done by the SA Government, their year-by-year account running up to 1912 stands in place of any formal Annual Report issued by the Government Geologist or staff. The 312 departmental Letter Books records are individually registered are limited to reports made by HYL Brown which the SA Minister of Mines in the day considered to have enough economic (and political) value for him to table during Government business in the SA Parliament. Tabled reports subsequently became part of the Parliamentary Papers archive. But other reports of scientific activity and those giving reasoned advice for suggested lines of technical research that should be pursued, which did not carry immediate cadence, were ignored for formal promulgation. Pre the federation of the states of Australia in 1899-1900, South Australia had governance responsibility for what became the Northern Territory of this country. Therefore, HYL Brown and his colleagues conducted the first extensive resource surveys of that large tract and write about their findings. Several expeditions were made to different parts of the territory during that time, building on and adding to the work done by famous prior explorers like Stuart. As such, the LB records are a major part of captured early NT history, re. advice guiding the decisions made about its development. The original Letter Book volumes are now stored at State Records Archival Repository, to ensure preservation, and due to their fragile nature can only be viewed under supervision onsite. Please contact State Records to arrange access. They are not yet available as scanned versions, again due to their fragile nature