On July 1, 1926 something happened in Canada that we know nothing about in recent years - postal rates actually went down! The rate for a one ounce letter within Canada dropped from three cents to two cents and the corresponding rate to the United Kingdom and the rest of the British Empire dropped from four cents to three.
Unfortunately, according to George Marler in The Admiral Issue of Canada, the Post Office had 130 million THREE CENTS carmine Admiral stamps (Scott #109) in stock, enough to last 25 years if they were only to be used to pay the new rate to the UK and British Empire!
To deal with this situation it was decided to surcharge the THREE CENTS Admiral with a two cent rate so that the stamps could be used for the new domestic rate.
Two different surcharges were used, a one line version (Scott #139) shown on the left and a two line version (Scott #140) shown on the right:
Much sought after by collectors of Admirals as well as Classic Era Canadian stamps, these now catalog for $85.00 and $42.50 respectively in MNH condition.