Dikes are very common. In some places you find the rocks fairly laced with them. The picture of the dikes in the granite shores at Marblehead also shows (in the horizontal plan) many "faults" or slips of the rock since the dike was made, and each slip probably gave rise to an earthquake. So you see there's the story of a terrible time written on those quiet old residents by the sea. [Illustration: THE GIANT'S CAUSEWAY Here is a still more striking example of the formation of columns in lava--the Giant's Causeway. Here are 40,000 columns, packed like the cells of a honeycomb, and they slope to the pavement in the foreground that gives the mass its name. That bees should make their little honey-jars in such regular form is wonderful enough, but think of lava shaping its own self into columns like that! ] DID MR. VULCAN USE A STEAM PILE-DRIVER? Just what power Mr. Vulcan used to drive the dikes is not known for sure, but I'll tell you how it is supposed to have been done. Remember that all rocks that are deep down in the earth contain water, shut up in their pores. Then remember how hot it is down there and how this heat would make steam right in the rocks. Then let the rock above be cracked by the movements of the earth crust, and this crack extend down to where these hot rocks are, the pressure, being released along that crack, the melted rock (lava) would rush up, as it does in connection with the eruptions of volcanoes, and the exploding steam would help drive it. III. Ancient Weather Records Turned to Stone So much for the literary remains of Mr. Vulcan. Now let's see how much we can make out of the handwriting of the waters and the winds on these walls of time. What does the picture at the top of page 245 look like? Rain-drops in the dust. And so you see they are; but the rain fell so long that the pits made in the dust have turned to stone. Think of the autograph of a rain-drop older than the Pharaohs; older than the pyramids these Pharaohs built to perpetuate their names.