Adam Sedgwick (1785-1873, APS 1860), geologist, was an important figure in the development of the modern discipline of geology. He was educated at Cambridge, being ordained in 1817. An excellent field geologist, he did significant work interpreting complex old rock in such places as Devonshire (naming the Devonian Period after that location), Cornwall, and the Lake District, correlating his findings with strata in places such as Germany. Sedgwick first interpreted strata from the period he named Cambrian. He served in many professional organizations and was honored for his work with the Wollaston and Copley medals. Sedgwick, a Liberal in politics, served on committees that reformed the administration of university education. Despite being a friend of Charles Darwin's, Sedgwick was critical of the materialist bent of Darwinian thought. The 37 letters in the collection were acquired at various times, mainly through purchase, and assembled for the collection. The letters span the dates 1825-1870. Individually most letters are not especially significant, but collectively they touch on most aspects of Sedgwick's life and career. There are letters about Sedgwick's work on university reform, the Geological Museum at Cambridge, lectures, colleagues, travel, health, and family. Only one letter in the collection delves into detail about Sedgwick's geologic work.

There is correspondence concerning geology, botany, natural history, natural selection, evolution, British science and scientists, and other scientific topics. Most of the letters are written by Lyell, with a very few items by others.