- 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.
- Wedgwood Rock (Wikipedia)
Wedgwood Rock is a glacial erratic (known to geologists as the Wedgwood Erratic) near the neighborhood of Wedgwood in Seattle, Washington. Its mineral composition matches that of Mount Erie, on Fidalgo Island in Skagit County, Washington, 55 mi (89 km) north. Prior to the establishment of the Wedgwood neighborhood, the erratic was known first as Lone Rock and later simply as Big Rock. Transported to its site by the Puget Lobe of the Cordilleran Ice Sheet during the Vashon Glaciation more than 14,000 years ago, it was a landmark for Native Americans in what was once a dense forest.