Uberwald is famed for its fat deposits, believed to have originated with the geologically spectacular demise of the Fifth Elephant which also gave rise to the various mineral deposits in the area, although silver has not been mined there for some time, because of the Diet of Bugs, wherein the werewolves and vampires agreed to leave each other alone, hence no need for the metal.
The fat deposits of Uberwald in particular are prized in such cities as Ankh-Morpork, where there is only Treacle Mine Road by which to remember one of the city's only forays into mining, mainly content to leave that in the hands of the dwarves these days.
The fat mines, however, can sometimes yield BCB's, or burnt crunchy bits (the fourth food group, after sugar, grease, and starch). These occur as a result of prehistoric animals having accidentally drowned in the fat pools, down to a crisp, presumably, as Terry Pratchett points out, "battered to death."