Now suppose where some great granite rock stood up through layers of other kinds of rock—looking as if it had pushed itself through like the great granite boss on which Edinburgh Castle stands—you found that wherever this intruder touched the other rock that rock was crystallized. If we had just found all this out for ourselves, as the geology people found it, we would say, just as they said:
FATHER, GRANDFATHER, AND THE CHILDREN IN THE PORPHYRY FAMILY
In this piece of porphyry you see three generations, all living under one roof, as it were. Notice that six-sided crystal near the centre? Compare it with other good-sized crystals that haven't any distinctive shape. The reason for the difference is that the shapeless ones have had some of their substance taken away to form the smaller crystals. The dark mass is lava. In it the big crystals formed. Then, from most of the big crystals the lava reabsorbed material, and this material later turned into little crystals—the "grandchildren" of the three generations.
"I wonder what the granite did to the limestone and the other rocks around it to make them 'sugar,' or, as we say when speaking of rocks, 'crystallize'? Syrup sugars when it is heated and then cooled without stirring. I wonder if this intruding mass that is now granite didn't spout up, in melted form, from down in the earth, and heat the rocks on either side as it burst its way through. Then both this hot rock and its neighbors cooled and crystallized. That's it!"
SPLITTING MARBLE ROCKS IN THE QUARRY
This is a scene in a marble-quarry. The men are splitting up a 120-ton block. A writer in Scribner's Magazine, in which this illustration originally appeared, also describes the process. The wedges, carefully greased, are inserted in the drill-holes which, for a horizontal split, are neither close together nor very deep, as that is the natural plane of cleavage between the strata. Two men with sledges go down the line giving each wedge a blow—not too hard. Then two more men follow, and in go the wedges a little farther. You see it wouldn't do to rush matters, or you'd fracture the marble. The operation is so delicate, indeed, that the foreman himself gives the final blows. Then the marble cracks from hole to hole. For the vertical splits the holes, you notice, are closer together. They are also deeper.
In some places you find these granite masses in great bosses, or domelike rocks; elsewhere in long strips, like an iron bar thrust through other rocks; in still other places in great slabs between other rocks, like a warming pan pushed between the bed-sheets on a cold winter night; but everywhere it touches other rocks these neighbors are crystallized.
Now, coming back to our friends the fossils, we sometimes find limestone bordering one of these intrusive marble rocks with fossils in it, shading off into limestone containing the same kind of fossils. As you get closer to the granite mass the fossils in the marble gradually fade away until you come to marble in which there are no fossils at all.