Shen Kuo was a polymath Chinese scientist and statesman of the Song Dynasty (960–1279). Excelling in many fields of study and statecraft, he was a mathematician, astronomer, meteorologist, geologist, zoologist, botanist, pharmacologist, agronomist, ethnographer, encyclopedist, and poet. He was the head official for the Bureau of Astronomy in the Song court, as well as an Assistant Minister of Imperial Hospitality. In his Dream Pool Essays of 1088, Shen was the first to describe the magnetic needle compass, which would be used for navigation (first described in Europe by Alexander Neckam in 1187). Shen Kuo devised a geological theory of land formation, or geomorphology, based upon findings of inland marine fossils, knowledge of soil erosion, and the deposition of silt. He also advocated a theory for gradual climate change, after observing ancient petrified bamboos that were preserved underground in a dry northern habitat that did not support their growth in his time. Shen Kuo wrote extensively about movable type printing invented by Bi Sheng, and because of his written works the legacy of Bi Sheng and the modern understanding of the earliest movable type has been handed down to later generations.