National Geographic : 1893 Jul 10
60 C. D. Walcott-The Natural Bridge. met with in passing up from the river are highly inclined lime stones and shales of middle or upper Cambrian age. These are succeeded by the massive Knox dolomites, which are nearly vertical or inclined slightly westward. A few hundred feet below Natural bridge the westward dip decreases very rapidly, and at the bridge the beds are nearly horizontal, while a short distance, above they are rising westward and dipping eastward toward the bridge at an angle of 5° to 100. This increases to 20° to 250 higher up the stream. A diagramatic section of the rocks cut through in the can yon of Cedar creek gives the outline shown in figure 1. The bridge is at A, Lace falls at B, and James river at C. No attempt is made to show the depth of the canyon or gorge through which Cedar creek flows. It is not supposed that the present Cedar creek began to wear its channel across the edges of the upturned beds from B to C when the present topographic features were established; on the contrary, it began its work long before, under conditions A a FIGURE 1. -Attitude of Strata at NaturalBridge. and in rocks that have since disappeared in the general erosion of the surrounding country. The course of the stream was determined by circumstances connected with the life history of James river. When the latter obtained a new lease of active life and lowered its channel through the Blue ridge, Cedar creek began to cut down its bed in the peneplain and to prepare the way for the possibility of the existence of an arch over its chan nel. The general mode of formation has long been described for this and other natural rock bridges. In this case in detail it is considered to be as follows: Cedar creek was engaged for a considerable period in excavating the gorge from the James river to a point not far below the present site of the bridge, where a fall appears to have existed, the summit of which was not far if at all below the present level of the top of the bridge. About this time the water found a subterranean passage in the limestone fur ther up the stream than the present site of the bridge, and through this it flowed and discharged beneath the brink of the falls.
1894 Jan 31
1893 May 05