 The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into layered metamorphic rock known as gneiss.In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been nearly melted in the procedure.Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period.