In the New York Botanical Garden, the river flows within a fault line and between cliffs of blended Manhattan Schist and Fordham Gneiss—rocks that have been metamorphosed, or changed, by the tectonic forces that shaped the region. The waterfall in the Garden is the remains of a dam that powered several mills that manufactured snuff between 1792 and 1870. The current Stone Mill (formally the Snuff Mill) was built in 1842 and underwent major renovations that were complete in 2010.