After an act of Parliament in 1750, England and its colonies had to change calendars. England was using the Julian calendar which was 11 days behind the Gregorian calendar used in the rest of Europe. To do this, they skipped September 3rd-September 13th.
In the Julian Calendar, New Years was on March 25. So December 31, 1750 was followed by January 1, 1750 and March 24, 1750 was followed by March 25, 1751.