1935. Those with the mint mark "B" were produced at the Bombay Mint; others, marked "C", were struck in Calcutta. Those with no mint mark were produced in London. The mint mark "C" can be found in the ground between the left foot of Britannia and the base of the shield, while the mint mark "B" is located in the center prong of the trident. The 1921-B dollar was struck but never released for circulation, and only a limited number of 1934-B and 1935-B coins were released. In some cases, the date on an already manufactured coin die was altered. As this could not be done without leaving a trace of the former date, some coins show traces of an older date below the clearly visible date. These include 1897-B over 1896-B, 1900-B over 1894-B, 1901-B over 1900-B, 1909-B over 1908-B, 1904-B over 1898-B, 1903-B over 1902-B, 1908-B over 1903-B, 1904-B over 1903-B, 1929-B over 1901-B, 1908-B over 1907-B, and 1910-B over 1900-B. The British trade dollar was demonetized on 1August 1937. United States The United States trade dollar is a silver (fineness of .900 or 90%) dollar coin that was issued by the United States Mint and minted in Philadelphia, Pennsylvania, Carson City, and San Francisco from 1873 to 1885. Business strike trade dollars were last produced in 1878 and proof coin production continued until 1885. The coin weighs 420 grains (27.2 g), about 8 grains (0.52 g) more than the domestic silver dollar (Seated Liberty Dollars and Morgan Dollars) of the time. It is 4 grains heavier than the Mexican peso; however, the peso is .903 silver. The coin was designed by William Barber, the mint's chief engraver. More trade dollars were minted in San Francisco than Carson City and Philadelphia combined. San Francisco was closest both to the source of the silver as well as the ultimate destination of the coins, China. Many Trade dollars have what are called "chopmarks" on them. Chinese merchants would stamp the coins in order to verify their correct weight and value. The United States Congress authorized the U.S. Mint to create a trade dollar to improve trade with the Orient, China in particular. Prior to that, the Mexican peso had been the primary silver coin used in trading with China. In fact, the eagle on the trade dollar's reverse looks quite similar to the peso's. Collectors are warned that recently a