Within the park, this type of falls usually flows over thin layers of Huntley Mountain Formation sandstone. In bridal-veil falls, the second type, water falls over a ledge and drops vertically into a plunge pool in the stream bed below. Within the park, this type of falls flows over Catskill Formation rocks or the red shale and sandstone of the Huntley Formation. In the park, the harder caprock which forms the ledge from which the bridal-veil falls drops is grey sandstone. The softer red shale below is eroded away by water, sand and gravel to form the plunge pool. While the official Ricketts Glen State Park web page also classifies waterfalls as either the bridal-veil or wedding-cake type, Brown's "Pennsylvania waterfalls: a guide for hikers and photographers" uses four types for classification: falls, cascade, slide, and chute. The first, falls, is the same as the DCNR's bridal-veil type, with water that falls freely from a ledge. Brown divides the wedding-cake class into three types: cascade, where water falls down a "vertical to nearly vertical" surface that has terraces; slide, where water falls down a "near vertical to less than vertical" wide surface that is smoother than a cascade; and chute, where the water is confined by rock as it falls down "a narrow slide or cataractlike feature". Ricketts Glen State Park is in the Susquehanna River drainage basin, the earliest recorded inhabitants of which were the Iroquoian-speaking Susquehannocks. Their numbers were greatly reduced by disease and warfare with the Five Nations of the Iroquois, and by 1675 they had died out, moved away, or been assimilated into other tribes. After this, the lands of the Susquehanna valley were under the nominal control of the Iroquois, who encouraged displaced tribes from the east to settle there, including the Shawnee and Lenape (or Delaware). On November 5, 1768, the British acquired land, known in Pennsylvania as the New Purchase, from the Iroquois in the Treaty of Fort Stanwix; this included what is now Ricketts Glen State Park. After the American Revolutionary War, Native Americans almost entirely left Pennsylvania. Luzerne County was formed in 1786 from part of Northumberland County, and Fairmount Township, where the waterfalls are, was settled in 1792 and incorporated in 1834.