 He inferred that the land was reshaped and formed by soil erosion of the mountains and by deposition of silt, after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou.Furthermore, he promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in the dry, northern climate zone of "Yanzhou", which is now modern day Yan'an, Shaanxi province.The term geomorphology seems to have been first used by Laumann in an 1858 work written in German.