Chunks of the overlying rock may break off and become a part of a sill. 上复岩石的碎块可能破裂并成为岩床的一部分。
In fact, this period of Canada's underground rock Chuangpi area of great scientists of the Earth's surface known as the oldest known. 事实上，加拿大的这段地下面积很大的岩床被科学家称之为地球表面已知的最古老的地方。
