Pillow lava their shape reveals the attitude, or position, in which they were originally formed. Pillow lava shows it is still in its original orientation when: Pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or "subaqueous extrusion". Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in diameter. They form the upper part of Layer 2 of normal oceanic crust. Pillow lavas are commonly of basaltic composition, although pillows formed of komatiite, picrite, boninite, basaltic andesite, andesite, dacite
West Rock Ridge in faults created by the rifting apart of North America from Eurasia and Africa over a period of 20 million years. Erosion occurring between the eruptions deposited deep layers of sediment between the lava flows and around the dike, which formed sedimentary rocks. The resulting "layer cake" of igneous and sedimentary sheets was later faulted and tilted upward. Subsequent erosion wore away the weaker sedimentary layers a faster rate than the lava layers, leaving the abruptly tilted edges of the lava sheets exposed, creating the distinct linear ridge and dramatic cliff faces visible today along the Metacomet Ridge. West Rock