The causes of the rise and fall of the sea coasts are many, and there are things about these movements not yet understood. By what wonderful machinery, then (we might naturally ask), were the continents themselves lifted out of the sea? To this, which would seem much the harder question of the two, the answer is simple; as simple as a baked apple. You know an apple that goes into the oven with a smooth, neat skin comes out covered with wrinkles. Now suppose, instead of a little, hot apple, covered with a thin skin, you have a big, hot earth covered with a thick crust of stone, and the inside of the earth shrinking all the time as the inside of the apple shrank away from its skin. The rock skin would wrinkle, and the wrinkles, rising out of the seas that then covered it everywhere, would make continents. [Illustration: THE RISE AND FALL OF JUPITER SERAPIS In this account of the ups and downs of land and sea I must tell you the story of Jupiter Serapis. In the days of the Romans this temple, for his honor, stood on the seashore near Naples. Of that temple only three pillars remain, but they answer a very important question. On these pillars, over twenty feet above sea-level, is a belt of holes bored in the stone by a certain shelled sea-creature, one of the barnacle family; so evidently these pillars must, at some time, have sunk, as shown in the second picture, and then risen again, as shown in the third, which represents them as they stand to-day. Another interesting thing is that the third picture--observe--shows a volcano that isn't in the other two. Following a series of earthquake shocks in 1538 the earth opened and out popped hot stones and ashes and built themselves into a small volcano right before everybody; for it was all done in a short time, and you may be sure the frightened people kept their eyes on it, and they named it Monte Nuovo, which is Italian for "New Mountain." ] "And God said, Let the waters under the heaven be gathered together into one place, and let the dry land appear: and it was so." According to the planetessimal theory the way in which the seas were made was this: Owing to the collision--the "bang"--of the planetessimals against the earth, and against each other as they met at the "terminal station," heat was generated. The compression, the squeezing together, of the earth from its own weight--the gravity pull of the whole mass toward the centre--generated still more heat, and the heat and pressure drove the gases out of the rock. These gases included hydrogen and oxygen. These two gases cooling and combining themselves, in a way they have, became water, and there were other gases, such as nitrogen and carbon gas, that helped to make the air. WHEN THE SEAS WERE ALL IN THE SKY