Gneiss and Sandstone Layers
July 14, 2003
The unconformity in the middle of the above photo marks the contact between the Proterozoic Era gneiss (at bottom) and the Potsdam conglomerate and sandstone (above). The gneiss dates to approximately 1.1 billion years (Grenville metamorphism), and the Potsdam layers formed during the Paleozoic Era -- middle to upper Cambrian Period. Note the nearly vertical banding in the gneiss as contrasted with the nearly horizontal and undisturbed bedding of the conglomerate and sandstone.