In the carboniferous age the air surrounding the earth was much warmer than at present, warmer than we find it in the tropics. The great mass which constitutes this globe was not yet cool enough to support any very high forms of life. There were no trees, as we now understand the word, and there was very little animal life. Beetles crawled about, spiders and scorpions, and salamanders big as alligators, but there were no mammals, no birdsThe world was in twilight, reeking with moisture, steaming in the warm air which it filled with all sorts of noxious gases. It rained aquafortis and brimstone, and the sweating earth sent these up again in deadly fog-banks of poisonous vapor
These were the conditions that our big rush loved. Its huge spongy stem and branches drank in life from the death-laden atmosphere. Its great creeping rootstocks soaked it up from the morass beneath and the rush grew luxuriantly. Its office was indeed a cleansing one, to purify the atmosphere and make it fit to sustain animal life. In time, as the huge primevaltrees reached maturity, they died, and the mighty stems fell back in the bog. Then came some great upheaval, some cataclysm of nature such as we find everywhere recorded in her rocky books. The land rose or sank, and the rocks and debris of the sea floor were thrown upon the decaying vegetation. It was pressed and compressed beneath this weight. The fronds of the huge ferns; the tall stems of the giant rushes; the monstrous club-mosses, and the primeval forest became a peat-bog. Still greater pressure—a longer lapse of aeons, and the peat became coal.