This collection centers on Brown's geological investigations in various areas of Scotland and England concerning fossils, geological formations, deposits, etc. His activity in the Edinburgh Geological Society is documented in the letters and in newspaper clippings. Several of the letters contain diagrams, also geological maps (manuscript and printed) of Edinburgh and its environs, drawn by Charles Lapworth.

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.

A miscellaneous collection of letters written by naturalist Louis Jean Rodolph Agassiz concerning a wide range of topics: natural history and naturalists, geology, mineralogy, fossils, publications, expeditions, and the Museum of Comparative Zoology at Harvard, which he founded.