The Preston journal is a single volume of 42 leaves, containing 80 pages of manuscript. It includes two separate travel narratives, authored by individuals acting as debt-collecting agents for the Philadelphia merchant and landowner John Field. The first and more substantial of the narratives is titled "Minutes of a Journey to the Westward for John Field" (1r); it was written by Samuel Preston during a 19-day trip on horseback through Pennsylvania, Maryland and Virginia, 11 February to 1 March 1788. Preston's journey took him from Philadelphia west to Lancaster, Middletown, Carlisle, Shippensburg, and Chambersburg in Pennsylvania; across "Mason and Dixon's Line" to Hagerstown and Williamsport in Maryland; over the Potomac to Martinsburg and Winchester in Virginia; and back to Philadelphia via Frederick, York, and Lancaster. Preston's journal runs to some 7500 words, with entries for each day of the trip. The narrative recounts his immediate business—i.e., seeking to resolve debts held by Field, ideally by collecting money from the debtors—but it also contains extended and engaging descriptions of the land, settlements, and commerce of the regions visited. Some of these settlements "beyond Susquehanna" were at this time adjacent to the backcountry, "and command[ed] the general run of the frontier Trade" (23r). The volume also contains a second, abbreviated journal by an anonymous writer, also a debt-collection agent for Field; this contains entries from 24 to 28 June 1788, and sees its author as far as Carlisle. Accompanying the volume is a certificate validating Preston's appointment to the judiciary of the Northampton County, Pennsylvania, Court of Common Pleas (1790).

Preston was, by all contemporaneous accounts, a voluble character, and his narrative is informed by opinion, digression, and not a little humor. The anonymous writer who took over his journal felt barely up to the task: "Influenced, in some measure (I confess myself) by the Example of that truly and literally great and exalted Genius S. Preston whose journal is contained on the preceding Pages and who has lately gone before me on the same Road and on a similar Occasion. I now begin an account of my Transactions on the present Journey—tho' without expecting to find Matter for so many learned and so many witty Observations as are contained in the preceding Work. . . ." (30v). For his own part, Preston concludes his narrative with the observation that he completed his trip ". . .in 19 days and spent in the whole Journey 9=4=6 considering the inclemency of the Season. . .few People would have went through the same fatigue in much less time and if this Journal is not wrote in a plain hand it was wrote altogether on my knee and not as difficult to read as many things I did." (28v).