In one particularly stunning passage, he describes a theory of land formation by sedimentation, and an evidence for coastline movement. Following is the Chinese text and my translation. I got the Chinese text of Meng Xi Bi Tan from the Project Gutenberg.
余奉使河北, 邊太行而北, 山崖之間, 往往銜螺蚌殼及石子如鳥卵者, 橫亙石壁如帶. 此乃昔之海濱, 今東距海已近千里. 所謂大陸者, 皆濁泥所湮耳. (卷二十四)
When I was in Hebei, I went north, Taihang Mountains on one side, and between cliffs, often seashells and stones like bird's eggs crossed stone walls like a belt. Once this was the seashore, now a thousand li east of the sea. So-called continents are all submerged mud. (Volume 24)
This insight is comparable to that of James Hutton, a Scottish geologist of the 18th century, who is considered the father of modern geology. In Concerning the System of the Earth, its Duration and Stability, printed in 1785, he wrote:
Hence we are led to conclude, that the greater part of our land, if not the whole had been produced by operations natural to this globe; but that in order to make this land a permanent body, resisting the operations of the waters, two things had been required; 1st, The consolidation of masses formed by collections of loose or incoherent materials; 2dly, The elevation of those consolidated masses from the bottom of the sea, the place where they were collected, to the stations in which they now remain above the level of the ocean.
James Hutton is often unappreciated, but he must be considered as an equal of Isaac Newton and Charles Darwin. He published one of the most profound idea in the history of science, that the Earth is old. Like Darwin's theory, his theory challenged Christian doctrine, since it was incompatible with the account in Genesis. And it was the idea that the Earth is old, a half century later, that let Darwin think there was enough time for all life to evolve.