These are primarily scientific letters from Buckland. The subjects mentioned include Milne-Home's seismological investigations, Wheatstone's self-registering instruments, geology (glacial phenomena in Scotland, mineralogy, etc.), numerous references to fossils, and mentions of Mastodon bones and sloths.

Series I is a miscellaneous collection of letters concerning geology, geological exploration of Russia, entomology, glaciers, appointments in the British Museum, Geological Society of London business, Royal Geographical Society, references to David Livingstone, and zoology. Series II consists of letters written from America, to Murchison, discussing geology, natural history, and contemporary topics.

This is a miscellaneous collection of letters, almost all written to Smyth by prominent scientists. The topics discussed include astronomy, microscopes, nautical almanacs, and submarine excursions. Also of interest is a letter from Thomas Graves, reporting what the Beagle (Charles Darwin's voyage) was encountering in South American waters.

One of the most important natural historians in nineteenth century Britain, Charles Darwin provided the first compelling mechanism to account for organismal evolutionary change. Although lacking a coherent model of heredity, Darwin's natural selection has exerted an enormous influence over the biological sciences and since the introduction of Mendelian genetics, had remained the key unifying principle in the discipline. The APS Darwin Papers are a large a valuable assemblage of Darwin's correspondence with scientific colleagues, including Charles Lyell and George J. Romanes. They are included in the print version of the Correspondence of Charles Darwin (Cambridge Univ. Press).