Long ago, the territory surrounding Winterfell was not prowled by direwolves, but rather by corals, fish, and perhaps the occasional reef shark. While we know that Winterfell’s protective walls are made of granite, the grey hue of the majority of the fortress suggests a different building material, which we interpret as limestone (a common building material during the middle ages on Earth). And limestone, if you have not already surmised, is formed by large “carbonate factories” typically associated with shallow seas and reefs. The evidence for limestone is indirect but compelling, and requires a step back to survey the territory surrounding Winterfell more broadly. To the southwest of Winterfell lie the Flint Cliffs (which we choose to interpret literally). Flint is a form of chert, a siliceous rock that forms on the shallow ocean floor. The proximity of shallow ocean rocks to Winterfell suggests an oceanic origin to the stones used to build the castle. The presence of caves used as crypts by the family Stark suggests karst topography, which is indicative of limestone and the “swiss cheese” geology associated with subsurface water eroding complex cave systems (think, Carlsbad Caverns in New Mexico, USA, or Waitomo Caves in New Zealand). The rapidly flowing subsurface water would also help explain the Green Fork River, originating near The Twins. The rivers that pass through The Twins are somewhat problematic given that the vast majority (~99.9%) of rivers on Earth begin in areas of higher elevation (like mountain ranges). Yet these rivers seem to simply appear, much like the Warlocks. We propose that these rivers originate from complex subsurface water pathways making their way to the surface through the chert and limestone, emerging as springs. Again, while indirect, the combined observations of grey building stones, flint, karst topography, and the Green Fork River strongly suggest that Winterfell sits near large limestone deposits.
Dating the Winterfell limestone is more complicated, but not impossible. Reefs on Earth only appear within a narrow range of latitudes, approximately 30° north to 30° south (at least in the modern climate – during warmer greenhouse conditions, the latitudinal range is much broader). Currently, Winterfell sits at near 60° north, far too cold for coral reefs, even during greenhouse conditions. This suggests that Winterfell, and indeed the entire continent, has moved over the eons, further supporting our early assertion of active tectonics. Earlier, we concluded that the limestone was likely uplifted during the Moon Orogeny, 80-100 Mya. Therefore, we know that the Winterfell limestone is older than 100 million years. More exact dating requires comparison to similar rocks on Earth: the Carboniferous Limestone of Great Britain and Ireland. The Carboniferous Limestone currently sits at similar (within 5°) latitude as Winterfell, and like the Winterfell Limestone, formed as ocean sediments much closer to the equator. The Carboniferous Limestone is approximately 350 million years old, and required an elongate and curvilinear journey to move from the tropics to its current location. We assume a more direct path for the Winterfell Limestone, and therefore place an approximate age of 280-300 million years.