There were various methods to keep butter over a period of time. The picture above is butter stored in a cabbage leaf, from the 'Feast for the Eyes' website.
A Pickle for Butter. Lea. Domestic Cookery. 1851
To Keep Butter. [brine] Presbyterian Cookbook. 1873
A Brine to Preserve Butter. Gillette. White House Cook Book. 1887
To Preserve Butter [Brine] The Good Housekeeping Dictionary of Facts. 1926 Cookery Hints
Salting to preserve butter. p207 Miss Beecher's Domestic Receipt book. 1850
To put up Butter for Winter. [salt] Lea. Domestic Cookery. c1851
Preserve butter. [salt, sugar, saltpetre] Beecher. Miss Beecher's Domestic Receipt book. 1850
To Cure Butter that will keep for a Length of Time. [salt, sugar, saltpetre] Lea. Domestic Cookery. c1851
Preserving Butter. [salt, sugar, saltpetre] Presbyterian Cookbook. 1873
Putting up Butter to Keep. [salt, sugar, saltpetre] Gillette. White House Cook Book. 1887
Preserved by boiling. Marcy. The Prairie Traveler. 1859 under 'Stores and Provisions'
Frozen outdoors and stored in granary
Shepard tree - Boscia albitrunca. roots preserve butter
Butterbur - Petasites hybridus. herb
Butter through the Ages website
From Hand Churn to Creamery webpage
The Butter Cross. Abbots Bromley
Butter Cross. Peterborough.
History of the French Butter Dish or Butter Bell
Foreign essays on agriculture and arts. Butter essay p229-234 London 1765
Butter Churns - many links