But the rock is real. At that time, there were no plants on land, nor fishes in the sea. The rock formed deep within the earth from magma. It didn't reach the surface of the land, but cooled very slowly into an igneous rock called granite. Notice the characteristic fine light and dark banding called foliation.
Joints are one of the most common features in the crust of the earth.
They are important in controlling the flow of water and consequently in the shaping of landforms. There will be more about joints at Point 2 . Check out the white pegmatite veins imbedded in the finely banded matrix of the gneiss. At some time, cracks opened which were subsequently filled with liquid, igneous material that cooled slowly. The rock exposed here in the tunnel and throughout Chimney Rock Park is called Henderson Gneiss, after the location where it was originally described in Henderson County, North Carolina.