At a later period in the world's history, a huge and mighty fissure must, reasoning by analogy, have been dug diagonally from the southwest to the northeast of the island, through which by degrees flowed the volcanic crust. The great and wondrous phenomenon then went on without violence—the outpouring was enormous, and the seething fused matter, ejected from the bowels of the earth, spread slowly and peacefully in the form of vast level plains, or what are called mamelons or mounds.