Cap-paper. A kind of writing paper in large sheets, usually called foolscap. — Webster, 1882
Fool’s cap. A long folio writing paper, about 13½ by 16½ inches. — Webster, 1882
Examination of all persons over the age of eighteen years, offering themselves as candidates for teachers’ certificates… All are expected to use pen, ink, and legal cap paper. — March 4, 1884, Dakota Pioneer
In By the Shores of Silver Lake (see Chapter 13, “Breaking Camp”), Charles Ingalls uses some leftover legal document paper to make up an “official-looking” fake summons in order to trick a man into paying for horses purchased from Mr. Boast. Why did Pa have legal cap in his possession? It may have been paper used in his duties running the company store, or it could have been brought from Walnut Grove, where Mr. Ingalls had been elected Justice of the Peace in March 1878 and again in March 1879.
Legal “cap” is short for “cap-paper,” a white writing paper that is significantly longer than its width, usually lined and with one or more margin lines (also called “down lines”) running vertically in red. Document blanks were a type of legal cap on which portions of a legal document were printed, with blank spaces left to be filled in as required. The image above is of a De Smet document from 1880.
Legal cap was typical stock carried by early printers and it could be purchased by anyone. The 1879 advertisement below from a Deadwood printer shows that legal cap sold for $1.25 per pound.
Legal pads were invented in 1888 by Massachusetts paper mill worker, Thomas Holley, who stitched together odd bits of paper leftover. A decade later, a judge requested that a red down-line be added so that he could write notes in the margin; if you look at old deeds, you’ll see that it was a common practice to make notations in legal-cap margins.
legal cap (SSL 13), see also writ of attachment