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. The Song dynasty philosopher Zhu Xi (1130–1200) wrote of this curious natural phenomenon of fossils as well. He was known to have read the works of Shen Kuo. Shen's description of soil erosion and weathering predated that of Georgius Agricola in his book of 1546, De veteribus et novis metallis. Furthermore, Shen's theory of sedimentary deposition predated that of James Hutton, whose groundbreaking work was published in 1802 (considered the foundation of modern geology). Historian Joseph Needham likened Shen's account to that of the Scottish scientist Roderick Murchison (1792–1871), who was inspired to become a geologist after observing a providential landslide. Meteorology Early speculation and hypothesis pertaining to what is now known as meteorology had a long tradition in China before Shen Kuo. For example, the Han dynasty scholar Wang Chong (27–97) accurately described the process of the water cycle. However, Shen made some observations that were not found elsewhere in Chinese literature. For instance, Shen was the first in East Asia to describe tornadoes, which were thought to exist only in the Western hemisphere until their observation in China during the first decade of the 20th century. Shen gave reasoning (earlier proposed by Sun Sikong, 1015–1076) that rainbows were formed by the shadow of the sun in rain, occurring when the sun would shine upon it. Paul Dong writes that Shen's explanation of the rainbow as a phenomenon of atmospheric