Manchuria consists mainly of the northern side of the funnel-shaped North China Craton, a large area of tilled and overlaid Precambrian rocks spanning 100 million hectares (250 million acres). The North China Craton was an independent continent before the Triassic period and is known to have been the northernmost piece of land in the world during the Carboniferous. The Khingan Mountains in the west are a Jurassic[33] mountain range formed by the collision of the North China Craton with the Siberian Craton, which marked the final stage of the formation of the supercontinent Pangaea.