Shen also wrote that since petrified bamboos were found underground in a climatic area where they had never been known to be grown, the climate there must have shifted geographically over time. Around the year 1080, Shen Kuo noted that a landslide on the bank of a large river near Yanzhou (modern Yan'an) had revealed an open space several dozens of feet under the ground once the bank collapsed. This underground space contained hundreds of petrified bamboos still intact with roots and trunks, "all turned to stone" as Shen Kuo wrote. Shen Kuo noted that bamboos do not grow in Yanzhou, located in northern China, and he was puzzled during which previous dynasty the bamboos could have grown. Considering that damp and gloomy low places provide suitable conditions for the growth of bamboo, Shen deduced that the climate of Yanzhou must have fit that description in very ancient times. Although this would have intrigued many of his readers, the study of paleoclimatology in medieval China did not develop into an established discipline.