1847 Unusual rate structure, Open mail via Boston.

1847 London, GB (Mar 3) to Guelph, CW, noted by US mail via Boston, USA, sent open mail and NOT closed bag, rated 13c ship letter at Boston (2c ship + 10c postage), converted to 7d, plus 2 1/2d = 7 1/2d Cy collect. The 1/2 Stg rate overpaid 2d stg and should have only been 1/- Stg at this time. Time was saved but the peculiar routing caused no money to be saved.