It was Shen Kuo who formulated a hypothesis about the process of land formation (geomorphology) based upon several observations as evidence. This included his observation of fossil shells in a geological stratum of a mountain hundreds of miles from the ocean. He inferred that the land was reshaped and formed by erosion of the mountains, uplift, and the deposition of silt, after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou. He hypothesized that, with the inundation of silt, the land of the continent must have been formed over an enormous span of time. While visiting the Taihang Mountains in 1074, Shen Kuo noticed strata of bivalve shells and ovoid rocks in a horizontal-running span through a cliff like a large belt. Shen proposed that the cliff was once the location of an ancient seashore that by his time had shifted hundreds of miles east. Shen wrote that in the Zhiping reign period (1064–1067) a man of Zezhou unearthed an object in his garden that looked like a serpent or dragon, and after examining it, concluded the dead animal had apparently turned to "stone". The magistrate of Jincheng, Zheng Boshun, examined the creature as well, and noted the same scale-like markings that were seen on other marine animals. Shen Kuo likened this to the "stone crabs" found in China.