- Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals. Changes in seismic wave velocities have shown that at a certain depth (the Conrad discontinuity), there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character.
- Field trip to the Wells Creek volcanics, North Fork Nooksack River (nwgeology.wordpress.com)
The Wells Creek Volcanic Member of the Nooksack Formation (Tabor and others, 2003; see refs below) is found in the vicinity of Nooksack Falls, east of Glacier, Washington. These Middle Jurassic island arc rocks form steep yellowish cliffs along the Mount Baker Highway (Route 542) just east of the Excelsior Pass trailhead, where they crowd the highway against the deep gorge of the North Fork Nooksack River…