He is best remembered for his study of the work of Timothy Pont, the 16th-17th c. cartographer, and published the history of his maps in two influential articles in Scottish Geographical Magazine, becoming "perhaps the most influential of Pont's many biographers". His 1901 article in the Scottish Geographical Magazine included a detailed description of Pont's father, the clergyman Robert Pont. Cash preserved the manuscript maps for the Blaeu Atlas of Scotland, some of which had been worked on by Pont between 1583 and 1596; Pont signed 36 of the maps that Joan Blaeu engraved. These manuscripts had "fallen into disarray", and Cash began by preserving them. He described and catalogued them, and collected and reviewed everything that had been written on them, and any material connected to the origin of the manuscripts and the maps as they were printed. Apparently he did such an exhaustive job that for the next fifty years nothing of importance was added. According to historian Jeffrey Stone, "the work of Cash represents a major advance in knowledge of the atlas, a major achievement which was preceded and followed by long periods of lack of either interest or success in scholarly work on the atlas".
