Page:Picturesque New Zealand, 1913.djvu/175

Rh "Now," began our instructor, "you are standing in an old crater, one of seventeen that were blown out between here and Tarawera, two of them in 1886. Until Waimangu erupted, this crater was a cold-water lagoon, and, as you see, part of the lagoon remains. Come over here and I will prove to you that the earth did not have to cool before it grew vegetation. The green growth on this rock is algæ, thriving in a temperature of one hundred and fifty degrees. Ten more degrees would kill it. These black pebbles are rhyolite bits coated on the upper side with iron pyrites, and on the lower side with oxidized iron."

Retracing, Ingle led us to where it was clearer, and instructed us in geyser and volcanic action. "Here is how geysers are formed," he explained. "The cold water constantly running into this hot pool is immediately expelled. And here is the Sponge Cake. The rock beneath its crust has been softened by condensing steam." Near the Sponge Cake was Ngauruhoe Junior, a small deposit of steaming sand. When Ingle made holes in it with a stick, sand and pebbles were thrown out, and where he pressed it with his foot, a small shower of sand was tossed up a few inches as soon as the pressure was removed.

As we listened to our thermal lecturer, our attention was drawn at intervals to a hoarse roar issuing from a rocky face near Gibraltar. It sounded like an ocean liner letting off steam, and it was emitted by Waimangu