Yule Marble is a marble of metamorphosed Leadville Limestone found only in the Yule Creek Valley, in the West Elk Mountains of Colorado, southeast of the town of Marble, Colorado. First discovered in 1873, it is quarried underground at an elevation of above sea level—in contrast to most marble, which is quarried from an open pit and at much lower elevations. The localized geology created a marble that is 99.5% pure calcite, with a grain structure that gives a smooth texture, a homogeneous look, and a luminous surface. It is these qualities for which it was selected to clad the exterior of the Lincoln Memorial and a variety of other buildings throughout the United States, in spite of being more expensive than other marbles. The size of the deposits enables large blocks to be quarried, which is why the marble for the Tomb of the Unknown Soldier at Arlington National Cemetery, with its die block, was quarried from Yule Marble. Yule's quality comes at a high price due to the cost of quarrying in a high-altitude mountain environment. This challenge has caused the industry and the town of Marble to undergo many boom-and-bust periods since quarrying started in the mid-1880s, making the town emblematic of the economic fluctuations that beset a single-industry economy. Technology advancements in quarrying machinery and transportation have reduced, but not solved, the cost problem that afflicts the operation through the present. Geology Development The forces that created Yule Marble make it distinct from all other American marbles. It was formed by contact metamorphism, unlike Vermont marble and Georgia marble, which are the result of regional metamorphism, a process more associated with the orogeny and erosion of mountain ranges on a regional scale. Geologists still debate over Tennessee marble which did not undergo the same type of metamorphism, leaving it in a very unique property somewhere between metamorphic marble and sedimentary limestone. In evaluating the marble cross-section, the United States Geological Survey found the marble is bounded above and below by unconformities. This lack of conformable contact resulted in the early dating of the limestone as Silurian rather than the currently accepted Mississippian. The lack of conformable boundaries in exposures along the Treasure Mountain dome explains the variation in reported thicknesses in the quarry area west of Yule Creek of about southeast of the quarry. The overlying Pennsylvanian Molas Formation was an argillite unit which was converted