The original letters make up the bulk of this collection. Perkins and his son created a book to preserve some of his letters, which spans a greater period of time than the letters themselves, which go only to 1945. Specific envelopes have been left with their corresponding letter if there was no indication of date anywhere except the envelope, and other envelopes have been collected if their postage, stamps, or other markings are notable. The remainder of the envelopes are preserved at the end of the collection. Perkins also used a series of 3.5 by 5 inch notecards to mark some of his letters as he sorted them for his book; although not every letter has a notecard, the notecards included are dated, and have summaries of what their letters included.