A superb unpublished group of original letters, including the only three known letters written by any crew-member of HMS Beagle during Darwin's circumnavigation, written to his parents by a literate and observant private in the Royal Marines. Included are particularly fine voyage letters from Rio, Montevideo and Valparaiso.

A superb unpublished group of original letters, including the only three known letters written by any crew-member of HMS Beagle during Darwin's circumnavigation, written to his parents by a literate and observant private in the Royal Marines. Included are particularly fine voyage letters from Rio, Montevideo and Valparaiso.

Burgess was bursting with pride about his adventures – "I have been in three quarters of the globe already" – and described taking the appointment through a combination of a spirit of adventure, the good money on offer and the hope that "if ever I do live to Come home I will be able to Sit Down and tell a good Story."

It is also attractive to note that in order for Burgess to be eligible for the soldier's concession postal rate of one-penny for each piece – far cheaper than standard post — the letters had to be authorised by a senior officer on board, meaning that his Beagle letters have the additional appeal of having been countersigned by officers on board, one by Bartholomew James Sulivan and two by the very long-serving John Clements Wickham.

Any original manuscripts dating from the Beagle voyage would be highly prized and keenly sought after, but Burgess's letters are doubly significant for the insight they give into the feelings and motivations of the otherwise overlooked and rather anonymous crew. Equally importantly, they provide remarkable details of the life of the "only member of the crew who left a record of his regard for Darwin in a series of letters written in 1875" (Darwin Online). Darwin was so fond of his old companion on the Beagle that he later sent him gifts of a carte-de-visite photographic portrait and a copy of one of his books (surely his account of the voyage, although it has not yet been discovered). Burgess and Darwin were almost exact contemporaries, which undoubtedly played a part in the understanding they shared, and it is also telling that neither showed even a glimmer of interest in going back to sea after their return.

Burgess (1810-1882) enlisted in the Marines in mid-1829 and was something of an old South America hand when the Beagle arrived in Rio in April 1832. He was snapped up by Commander Fitzroy very quickly (the cannier captains of survey vessels were very prompt to find and poach well-regarded sailors) and went on to make the entire voyage of discovery proper (1832-1836). Burgess was clearly well-regarded, not only by Darwin but also implicitly by FitzRoy, who is known to have paid particular attention to every aspect of his outfitting and boasted of enjoying the luxury of "a choice of volunteers to fill vacant places" (FitzRoy, Narrative, p. 21).

All six of the letters are addressed to Burgess's "dear father and mother" with whom he was very close, and all are perfectly clear and legible despite his charmingly erratic spelling. The group begins with his announcement of his first commission on HMS Tyne in mid-1830 and concludes with his 1837-dated letter of discharge from the Marines, and therefore takes in the entire span of his sea service. In the earlier letters Burgess memorably describes his appointment and voyage out, the adventure of his first crossing-the-line ceremony, his time on the South American flagship Warspite and then on the small tender Adelaide (a captured slave ship) which was sent to salvage bullion from the wreck of HMS Thetis, all leading up to his proud acceptance of a position on board the Beagle.

The early letters therefore provide an important introduction to the three shipboard letters sent from the Beagle, which amply record the excitement and the rigours of the expedition. It is clear that Burgess grappled with some of the scenes he witnessed and which he hastened to describe for his family at home: the different languages and confused interactions with the local people; the hardships of their work in Bahía Blanco and other parts of the survey; the forbidding coastline of Tierra del Fuego; the rough life of the Patagonians who come alongside in their canoes, their faces painted in red, black and white making them look – in his unusual simile – like so many "merry andrews"; or the devastation of parts of the Pacific coast by the earthquake of 1835. Burgess took enough of an interest in the remarkable scenes playing out before him that he has since been proven to have been the otherwise unnamed "sentry" who woke Darwin and brought him on deck to witness a volcano erupting while they were at anchor on a cold night off Osorno in January 1835.

The letters prove that Burgess was fully alive to the extraordinary scenes he was witnessing. This must also be why he treasured a piece of whale-tooth scrimshaw carved by one of his fellow Marines on the voyage, which featured scenes including one depicting four Fuegians in a canoe (now held by the Wardlaw Museum of the University of St. Andrew's).

The rediscovery of these letters not only restores a forgotten voice but gives shape to the experiences of the small and select group of Marines who protected the ship during its arduous circumnavigation. They provide an extremely uncommon insight into the forgotten men who made the voyage with Fitzroy and Darwin.