In terms of mine geography as it relates to the geology and fold structures, the large-scale synforms and antiforms have smaller scale fold structures associated with them termed “ledges”. If these ledges are synclines, they are odd numbered from east to west (3, 5, 7, 9, 11, and so on) and if they are anticlines, the structures are appropriately even numbered (6 and 10 ledges are the most significant). The exception to this is found in the historic, easternmost ledges that are termed Caledonia and Main ledges; Main Ledge was the most prolific ore system in the mine that technically starts out as an anticline and down-plunge, the ore progressively rakes across the structure and favors the synclinal part of the fold. Over 40 million ounces of gold were produced from all of the ledges that were mined during the 126 year history of this world class gold deposit that is the prototype for Precambrian iron formation-hosted gold deposits.

http://homestake.sdsmt.edu/Geology/geology.htm

См. также:
http://www.maine.gov/doc/nrimc/mgs/explore/bedrock/sites/jul...
http://en.wikipedia.org/wiki/Ledge
http://www.multitran.ru/c/M.exe?a=3&s=������&sc=78&l1=2&l2=1