We must pass on. Next comes a period called the Devonian, or Old Red Sandstone, when the Old Red rocks of Devon and Scotland were laid down. These contain remains of many varieties of very remarkable fish. A long period of coral seas succeeded, when coral reefs flourished over what was to be England; and their remains formed the Carboniferous Limestone of Derbyshire and the Mendip Hills. A period followed of immense duration, when over pretty well the whole earth there seem to have been comparatively low lands covered with a luxuriant and very strange vegetation. The remains of these ancient forests have formed the coal measures, which tell of the most widespread and longest enduring growth of vegetation the world has seen. Strange as some of the plants were--gigantic horsetails and club-mosses growing into trees--many were exquisitely beautiful. There were no flowering plants, but the ferns, many of them tree ferns, were of as delicate beauty as those of the present day. Many of the ferns bore seeds, and were not reproduced by spores, such as we see on the fronds of our present ferns. That is a wonderful story of plant history, which has only been read in recent years. After the long Carboniferous period came to an end followed periods in which great formations of red sandstone were made,--the Permian, and the New Red Sandstone or Trias. During much of this time the condition of the country seems to have resembled that of the Steppes of Central Asia, or even the great desert of Sahara--great dry sandy deserts--hills of bare rock with screes of broken fragments heaped up at their base,--salt inland lakes, depositing, as the effect of intense evaporation, the beds of rock salt we find in Cheshire or elsewhere, in the same manner as is taking place to-day in the Caspian Sea, in the salt lakes of the northern edge of the Sahara, and in the Great Salt Lake of Utah.