INFLUENCE OF THE FALLS LEUCOGNEISS ON THE HUMAN HISTORY OF WAKE COUNTY, NORTH CAROLINA

The Falls leucogneiss (FL) is an elongate, metamorphosed and deformed, magnetite-bearing leucogranitic pluton of Late Proterozoic age that intrudes gneissic rocks of the Raleigh terrane in the eastern Piedmont of North Carolina. Its western edge lies along the Late Paleozoic Nutbush Creek fault zone, and it is characterized by a pervasive, NNE-trending, subhorizontal stretching lineation and a strong aeromagnetic signature. The FL runs from south-central Wake County near Lake Wheeler northward to the vicinity of Henderson in Vance County. The unit constitutes a pluton that, in map pattern, measures about 70 km long and averages 1-1.5 km wide.

The FL was a favored local building stone; beginning as early as the mid-19th century and continuing until the late 1970's many small quarries were worked along its length, some near what is now downtown Raleigh. The stone's distinctive appearance makes it easily identifiable in existing structures, including a number of older homes, churches, schools, retaining walls and foundations.

The mica-poor FL is more resistant to weathering and erosion than the surrounding metamorphic rocks, and it thus defines a topographic lineament along much of its trace. The FL exerts a strong influence on stream geomorphology, and many of them flow parallel to it, thereby influencing development and road construction. Still, the major direction of streamflow across this part of the Piedmont is toward the SE or ESE, and some streams cross the FL at approximately right angles. For such streams, an abrupt increase in gradient, narrowing of the valley and decrease in width of the floodplain, as well as rapids and waterfalls, mark their courses where they cross the Falls leucogneiss. These locations defined a local Fall Line for early settlers, and were favored sites for the construction of mills and dams. Historic mills in Wake County at these sites included Lassiter Mill (on Crabtree Creek), Yates Mill (Steephill Creek), and a succession of mills at Falls of the Neuse. Of these historic buildings, only Yates Mill still remains. Located on university land, it has recently been restored and is a now a county park. Today a small dam remains at the Lassiter site on Crabtree Creek, while larger dams have been constructed on Swift Creek, Walnut Creek, and the Neuse River, to serve recreational and water-supply needs.