Structure of the Earth discontinuity (a second order discontinuity). The uppermost mantle together with the crust constitutes the lithosphere. The crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the seismic velocity, which is most commonly known as the Mohorovičić discontinuity or Moho. The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar (above) to rocks that contain no feldspars (below). Second, in oceanic crust, there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites, which has been observed from deep parts of the oceanic crust that have been
The Adventures of the Wilderness Family to the cabin to get his parents, Jenny goes after Crust, who has managed to scare the bear away. Skip is informed by Toby of what happened, and he heads out with his rifle to find his daughter. While trying to find their way back to the cabin, Jenny and Crust are attacked by a pack of gray wolves who chase them down to a nearby lake and almost attack Jenny. Crust is able to fend the wolves off long enough for Skip to arrive in the nick of time and drive the pack away. Despite this frightening encounter, Jenny