Gravel is a loose aggregation of rock fragments. Gravel is classified by particle size range and includes size classes from granule to boulder sized fragments. In Ymir it is are a common source of flint found in every biome and litter the map on high elevation tiles, hills and mountains. Gravel is the first resource you are able to exploit in the game (via a flint collector) along with hunting spots and wild crops. Gravel tiles provide only 1 ground fertility.